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WATER & SOIL
TECHNICAL PUBLICATION
No. 20
Regional Flood Estimation
IN
New Zealand
Water & soil technical publication no. 20 (1982)
,?,.t' :'; ISSN 0110-4144

WATER & SOIL TECHNICAL PUBLICATION NO. 20
iï
Regional Flood Estimation
in New Zealand
"$'
M.E. BEABLE & A.l. McKERCHAR
Head Office
Water and Soil Science Centre
wãiãtã"d Soil Division Water and Soil Division
MWD
MWD
Christchurch
Wellington
WELLINGTON 1982
Water & soil technical publication no. 20 (1982)

Regional flood est¡mat¡on in New Zealand
M.E. BEABLE & A.l. McKERCHAR
Head Office
Water and Soil Science Centre
Water and Soil Division Water and Soil Division
MWD
MWD
Ìùr'ellington
Christchurch
Water & Soil Technical publication No. 20. t9g2. t32p. ISSN Olt}_4lu
AbsÉract
eastern and western parts of the British Isles.
National Llbrary of New Zealed
Cataloguing-in-E ublication data
BEÀBLE, M. E. (Mlchael Eduard), I94Z-
RegionêL flood estj-nation / M.E.
Beabl€ r À-I. McKerchâr. - útellington,
N.Z. : úùater ðd Soll Dlvision Ministry
of Works ed DevoloE[ent for the
Nåtlonal Watêr md SoiI Conservâti,on
oEganisatLon. f992. - I v. - (gtater E
soil technical publícatlon, ISSN OIIO-
4144 ; no. 20)
5s1.4890993I
1. Flæd forecaating. I. McK€lchar, À. I.
Allstalr lan), 1945- . Ir. Tltlê.
III. Series.
O Crown copyrighf 19t2
Published for the National water and Soil conservation organisation
by the vy'ater and soil Division, Ministry of works and Devãlop¡nent,
P.O. Box lz-0/l, tr)Vellington, New Zealand
Water & soil technical publication no. 20 (1982)

I
1.1
1.2
1.3
Contents
¡ntroduct¡on
PageT
Introduction 7
Return period, risk and design life 7
Methods for estimating design floods 7
1.3.1 Empirical methods 8
1.3.2 Unit hydrograph methods 8
1.3.3 Simulation methods 8
1.3.4 Regional flood frequency methods 9
2 Gollection of data
2.1 Climate of New Zealand
2.2 Selection of catchments
' 2.3 Sources of data
2.4 Qualityofdata
2.5 Historicalinformation
poge ll ll
ll
ll
ll
ll
3 Regionalflood frequency analysis page 13
3.1 Flood frequency method 13
3.1.1 General 13
3.1.2 Terminology 13
3.1.3 General extreme value distribution 15
3.1.4 Sampling proPerties 16
3.1.5 Types of samPle 17
3.1.6 Plotting 17
3.1.7 Computer Programs
18
3.2 Flood frequencY data l8
3.2.1 Data collection 18
3.2.2 Minimum record length and outliers 19
3.2.3 Lake outflows 19
3.3 Flood frequency regions 19
3.3.1 Regional boundaries 19
3.3.2 Development of regional flood
frequencycurves 24
3.3.3 Bay of PlentY region 37
3.3.4 Final regional curves 39
3.3.5 Consistent regions 39
3.3.6 Sub-regions 39
3.3.7 Generalised flood frequency curves 42
3.4 Flood frequencyaccuracy 4
3.4.1 Accuracy of flood frequency ratio
Qr/Q
M
3.4.2 Datalimitations 48
3.4.3 Definition of flood frequency regional
boundaries 48
3.4.4 HomogeneitYtest 49
3.5 Flood frequencY discussion 49
3.5.1 Regional differences 49
3.5.2 Comparison with the British Isles 50
3.5.3 Variation within a region 50
3.5.4 Secular climatic variation 50
3.5.5 Extension method 52
3.5.6 Catchment size 52
3.6 Summary 52
4 Estimat¡on of mean annualflood puge 53
4.1 Introduction 53
4.2 Proposed method 53
4.3 Recôrds used 53
4.4 Collection of characteristics 53
4.5 Analysis of South Island data
4.5.1 Preliminary examination of data
4.5.2 Development of trial
regional estimators
4.5.3 Examination of residuals
4.5.4 Finarl equations for South Island
4.6 Analysis of North Island data
4.6.1 Preliminary analysis of data
4.6.2 Development of trial
regi,cnal estimators
4.6.3 Final equations for North Island
4.7 Discussion of results
4.E Comparison with other results
4.9 Estimation of coefficient of variation
4.10 Accuracy crf equations
4.11 Summary
5 Application
5.1 Introduction
5.2 Applicability
5.3 Design straJegy
5.3.1 General
5.3.3 Estimation of the flood peak for a return
79
79
Nelson area
D Revised 1224 estimates
E Comparison of method with TM61
F Flood frequency analysis for Otago
and Southland
F.1 Introduction
F.2 ' Data collection
F.3 Analysis and results
F.4 Conclusions
ReferenceS
58
58
58
63
& 66
6
69
7t
7t
72
72
76
poge77
77
77
77
77
5.3.2 Estimation of the mean annual flood (Q)
77
period T (Qr)
5.4 Examples
6 Summary
References
page83
Appendices
A Tests w¡th frequency distdbutions poge87
4.1 Introduction 87
A.2 Gamma distribution 87
4.3 Methods used 87
4.4 Evaluation of the frequency
analysis methods 88
4.4.1 General 88
4.4.2 Evaluation criteria and method 88
4.4.3 First test 89
4.4.4 Second test 90
4.4.5 Conclusions 9l
References 92
B Summary of the flood peak data used in the
regionalflood frequency analysis 93
C Summary of the new flood peak data in the
85
r06
107
t22
123
t23
t23
126
126
t26
Water & soil technical publication no. 20 (1982)

Tables
1.1 Risk ofexceedence for specified L and T pageT characteristics
ó4
4.E Stepwise regressions for all the North Island data 67
l6 4.9 Stepwise regressions for first trial North lsland
22 regions 67
4.10 Stepwise regressions for final North Island regions 69
4.ll Comparable equations for other countries 72
4.12 Prediction errors and equivalent lengths of record 75
5.1 Ranges of catchment areas used to derive regional
flood frequency curves and mean annual flood
equations 77
3.1 The relationship between y and T values for the
EVI distribution
Flow stations used
3.2
3.3
3.4
3.5
3.6
3.7
3.8
Calculations for extending the set of average values
for the Bay of Plenty region 37
Summary of the regional curve characteristics 39
Summary of flow stations in the Nelson area 42
Calculations for extending the sets of average values
for the generalised curves 42
Summary of the cha¡acteristics of the
generalised curves 44
The regional regression equations for
estimating Cp 47
3.9 The grouping and the group equations for estimating
Cp 48
3.10 The CF equations derived for the
generalised curves
48
4.1
54
4.2
56
4.3
l+q
¡1.5
4.6
4,7
South Island catchment characteristics
North Island catchment characteristics
Correlation matrix for logs of the South Island
characteristics
Stepwise regressions for all the South Island data
Stepwise regressions for the South Island regions
Final equations for the South Island regionJ
Correlation matrix for logs of the North Island
58
6l
63
g
5.2 Summa¡y of example results using the Regional
Flood Estimation method
4.1 Details of the flow stations used in the first
evaluation test
^.2 Summary of the performa.nce of the methods
in the first test
4.3 Details of the flow stations used in the second
evaluation test 90
^.4 Summary of the performance of the methods in
the second test 90
E.1
F.1
F.2
F.3
Comparison of Q.¡ estimates with TM6l estimates
(Qf) and regional flood estimation estimates 122
List of catchments
123
New flood peak data
lu
Co-ordinates from regiona-l frequency curves 126
gz
g9
g9
2.1 Number of water level recorder stations in New
Zealand and time distribution of water level data
page 12
3.1 pdf (part a) and the Of (part U)
ution 13
3.2 Fig. 3.1 as a function of its
4
Figures
4.2
4.3
4.4
4.5
4.6
4.7
4.E
4.9
4.t0
4.tl
4.12
5.1
5.2
F.1
F.2
F.3
F.4
F.5
F.6
F.7
F.E
F.9
F.10
!.ocation of the North Island catchments 57
Q vs A$.EA, South Island catchments Sg
Distribution of residuals from Equation 4.3 û
Plot of errors (log Q - O.SZ log AREA) vs log
MARAIN forEasr Coast Region
Logarithmic residual errors for trial South lsland
regional equations 62
Logarithmic residual errors for fïnal South Island
legional equations
ó5
Q vs AREA, North Island catchments 6
Trial regions for the North Island
6g
Final regions for the North Island 70
Distribution of Cy of annual maxima for the
South Island stations 73
Distribution of Cy of annual maxima for the
North Island stations 74
Flow chart of the design strategy using the Regional
Flood Estimation method
Water & soil technical publication no. 20 (1982)
Location of the Motu catchment above Houpoto g0
Location of catchments 127
Plot of normalised flood frequency data for lake
inflows and Shotover River superimposed on the
West Coast data given in Figure 3.13 l2g
Plot of normalised flood frequency data for the
Pomahaka River and the Southland Rivers l}g
Plot of normalised flood frequency data for East
Otago rivers superimposed on the South Canterbury
datagiven in Figure 3.15
l2g
Average points from Figures F.2, F.3 and F.4
Regions inferred from plots of flood
6l
7g
l2g
frequencydata 130
Frequency analysis of annual maxima derived for
Clutha river tributaries and the lakes, Manuherikia
and Waiau river tributaries. Regional frequency
curves ¿ìre also shown
l3l
Hydrographs of Shotover, Cleddau and Lake
Wakatipu inflow, 197l-1979
l3l
Hydrographs of two stations in the Southland
region, 197l-1980
ßz
Hydrographs of three Otago stations, l97l-19g0 132

a
A
â¡, âz
b', bt
c
C¡
Cp
C¡
Cy
Cvj
cs
df
EV
EVI
EV2
EV3
E()
F()
f()
GEV
i
J
K
k
k
L
LP3
M
m
fn
n¡
N
Nc
NU
P()
pdf
Pt
a
Qi
Qr
a
Q..,
Qrn"*
Qmed
Qous
r
R
se
S
S¡
t
T
u
var( )
x
Xa
i
v
YN
a
lL
I
02
Notation
Constant of regression equation
Catchment area (km':)
Constants of regression
Exponents of regression equation
Constant in a standard error equation
3::ü:i:Tl :ÎiiÏ"Ià" or estimare or er/Q rrom a curve ror given r
Coefficient of variation of prediction of Q
Coefficient of variation of regression estimate of Q
Coefficient of variation of annual maxima flood series
Coefficient of variation of annual maxima at jth station
Sample coefficient of skew
Distribution function
Extreme value
Extreme value tYPe I distribution
Extreme value type 2 distribution
Extreme value tYPe 3 distribution
Expected value
Distribution function
Probability densitY function
General extreme value distribution
Rank of a flood peak
The additional påriod of record, in years, outside the continuous rec¡rrd
Frequency factor
GEV shape parameter (ChaP. 3)
Number of stations in a region (Chap. 4)
Projected lifetime of a structure (Chap. l)
Log-Pearson tYPe 3
Toial length of station years spanned by the data in a group
Constant in a standard error equation (Chap. 3)
Number of independent variables in regression equation
Length of record at jth station (years)
Length of record (Years)
Average length of record in a region (yearÐ
Period of recording necessary to estimate Qo6. with the same accuracy as Qest $ears)
Probability
Probability density function
iainfall ráte (mm7t¡r) rãi-¿esign storm of duration t equal to time of concentration for catchment, and return
period T
Flood peak variate
An individual annual flood Peak
The flood peak estimate for a return period T
The mean annual flood
Q estimated from regression equation (m3ls)
Maximúm annual flood Peak
Median of the annual flood Peaks
Q estimated from flood record (m'/s)
iltt of one or more floods exceeding Qr in L years
Rainfall factor (Chap. l), Multiple córrelation coefficient (Chaps' 3" 4)
Standard error
Catchmentshapefactor-(Chap'l)Samplestandarddeviation(Chaps'3'4)
Standard error of logroQest
Student "t" statistics
Return period (Years)
GEV location Parameter
Population variance
Variate
Quantile estimate of variate x
Sample mean of variate x
Redúced variate for the EVI distribution
Reduced variate for the Normal distribution
GEV scale Parameter
Population mean
Intärstation correlation between annual maxima
Population Variance
Water & soil technical publication no. 20 (1982)

Preface
Water & soil technical publication no. 20 (1982)

1 lntroduction
1 .1 lntroduction
Many works and structures associated with natural
waterways are subject to flooding. These range from small
farm dams and culver'-s on minor roads, through flood
protection works and. major bridges, to major dams. In
designing these works, engineers have to estimate the
magnitude of the flood which is to be withstood during the
projected life of the structure. An appropriate estimate of
this "design flood" is fundamental to ensuring that
economic engineering designs with adequate standards of
safety are acheived.
Flood estimation for design purposes can be carried out
using either the deterministic concept of a "maximum probable
flood" for a particular catchment, or with the
statistical concept of a "flood magnitude with a probability
of exceedence". The former (Dalrymple 1964) is used
where exceedence of the design level could lead to
catastrophic failure. The object is to estimate the flood that
is unlikely to be exceeded. The method first estimates a
maximum rainfall for the catchment and then the corresponding
flood peak assuming the catchment to be in a
condition which would lead to maximum runoff. Since
neither the maximum rainfall nor the maximum runoff for
known rainfall can be estimated with certainty, the word
probable is used when no specific probability is given. In
contrast, statistical methods attach specific probabilities to
flood magnitudes.
Recent decades have seen the widespread use of benefitcost
analysis methods for assessing the relative merits of
different projects competing for capital resources. For projects
where flood magnitude is a design pararneter it is
necessary to attach specific probabilities to this magnitude.
Then the expected cost of flood damage can be balanced
against the cost of providing enhanced protection.
1.2 Return Period, Risk and
Design Life
In New Zealand the need to ensure the safety of major
hydro-electric developments stimulated an early interest in
flood estimation methods. Benham (1950) introduced a
statistical flood estimation method that has been used ever
since. In this method the design flood Q1 is defined as the
flood which is exceeded on average once in T years; T is
termed the return period, and Q.¡ is termed the T-year
flood which has a probability of exceedence in any one year
of l/T. Il the projected life of the structure is L years and
assuming independence of annual maxima, the risk r of at
least one T-year flood occuring in L years is;
r=l-(l-l/T)L
This expression is evaluated for a range of L and T
values in the Table l.l (it is presented graphically by
Ministry of Works and Development (1979) ).
10
50
100
20,0
Table 1.1 Risk of exceedence for specified L and T.
T=10 T=50 T=10O
0.651
o.995
1.OOO
1.OO0
0.1 83
o.636
o.867
o.982
o.096
o.395
o.634
o.866
T=
1000
o.o10
o.o49
0.095
o.181
Thus, for example, the probability of the lü) year flood
being exceeded at least once in a ten year period is 0.096' in
50 years 0.395, and in 100 years 0.634. This reasoning ap-
plies to one river, and the probability ofexceedence during
a specified time inl.erval at any one of a number of rivers is
much greater. If say l0 independent river basins and a l0
year period are considered, the probability of at least one
100 year flood being exceeded in any one of the l0 basins is
0.634 and the protrability of at least one 1000 year event is
0.095. Thus large floods are not remote events for consideration
by a feur specialists, but real possibilities of concern
to the whole community. Risk is a difficult concept to
convey to the wider community which is easily lulled into a
false attitude of complete safety. The risk of flooding to a
community is perhaps best conveyed by comparison with
the risk of other hazards that are tacitly accepted. Examples
include the risks of earthquake damage, traffic accidents
and nuclear power plant accidents. Pilgrim and
Cordery (1974) and Burns (1977) provide useful discussion
and further refere:nces on this subject.
In practice, r and L are often unstated and a fixed value
for T is used for a particular class of works. Thus in New
Zealand hydro-electric earth and rockfill dams, and dams
subject to the risk of progressive failure on overtopping,
have been designed to pass the 1000 year flood, while concrete
dams not sutrject to the risk of progressive failure on
overtopping are dersigned for the 500 year flood. Similarly,
state highway bridges are designed to pass the 100 year
flood, while culverts for state highways are generally
designed to pÍrss the l0 year flood without heading-up and
the 100 year flood with heading-up to a maximum level of
0.5m below the road surface. For some smaller structures
no clear standards exist and in some cases there is a lack of
rationality. Situations exist where authorities with
statutory responsiìoility for one part of a catchment adopt
higher design stanclards than a second authority in the same
catchment for the same class of work (Heiler 1975).
Selection of a design recurrence interval is a subject
deserving careful attention. For the credibility of designers,
its interpretation as a socially tolerable risk is information
that should be carefully explained.
1.3 Methods for Estimating
Desiç¡n Floods
The engineer must estimate a design flood in a range of
design situations. This design flood is a hypothetical flood
which results from a design rainfall over a catchment,
usually assumed to be in an average state of wetness. It is a
quantity with a probabilistic meaning defined in the
previous section and must be distinguished from forecasts
of actual floods which result from real rainstorms over a
catchment and whose magnitudes will depend on the prior
states of wetness of the catchment. This distinction is important
because

annual flood Q (the mean of the annual peaks). Q
may be estimated from measured catchment and
climatic characteristics. This is the method used in
this study. It is also known as the index flood
method. Another version of the method relates Q1
directly to catchment and climatic characteristics.
It is pertinent to review the development of all these
techniques in the New Zealand context.
1.3.1 Empirical Methods
Early flood estimation methods involved fitting an
envelope curve to observed extremes for a region to give an
empirical estimate of a maximum flood, usually with catchment
area as a parameter (Schnackenberg, 1949). Envelope
curve methods have been largely replaced by empirical
methods involving probability; of these the best known are
the Rational Method and Technical Memorandum No. 6l
(TM6l) (NWASCO l97s).
Although the Rational Method is in wide use, it is not an
accurate deterministic description of the way in which a
catchment modifies rainfall to yield the peak runoff
(French et al. 1974). An alternative and useful interpretation
of the Rational Method is statistic¿l. Here the method
links runoff rates of given frequencies with rainfall rates of
the same frequencies as follows:
Qr = C.Pt. A/3.6
where
qt: peak discharge rate of return period T (m¡,zs)
Pt = the design rainfall rate (mm/hr) for a storm of return
period T and duration t equal to the time of concentration
for the catchment
A = the catchment area (km,)
C = an empirical coeffìcient which provides the link between
peak runoff and peak rainfall. It embodies the
net effect of catchment losses, storage effects, etc.
French et al. (1974) showed that the coefficient C increases
somewhat with the return period T, and gave
typical values for central and south-east New South Wales.
Aitken (1975) found this ratio for a catchment to be
essentially constant for different return periods. For urban
catchments Schaake et al. (1967) suggested C could be
estimated as a function of the portion of impervious area in
the catchment and the slope of the main channel.
The second quantity requiring estimation is the duration
of the design rainstorm. The critical duration is closely approximated
by the minimum tirne of rise for a number of
hydrographs, These are not available for ungauged catchments
and traditional time of concentration formulae are
not reliable. Heiler (1974) developed an estimator for this
time constant for catchments of peninsular Malaysia. Once
a duration is established, storm rainfall can be estimated,
and in Heiler's case C was estimated as a function of rainfall
intensity; application of the method was restricted to
catchments with areas in the range I km, to 100 kmr. Adaptation
of this statistical interpretation of the Rational
Method for New Zealand conditions would be a valuable
contribution.
Another well-known empirical method in New Zealand
is known by its publication number, TM6l (NWASCO
1975) and is an adaptation of various American methods.
It is recommended for catchment areas up to 1000 kmr.
The method is;
Qr = 0.0139 CRSA%
where
C = coefficient dependent on the physiography of the
catchment,
R = rainfall factor dependent on the design storm,
S = catchment shape factor,
A : catchment area (km'z),
The factor C is determined as the product of two factors
ìV¡s and Ws. Wlc is determined from a table which has soil
type and surface cover as parameters, and W5 is obtained
from a graph having channel length and slope as
parameters. R is the ratio of the design rainfall for the catchment
to the adjusted standard rainfall at Kelburn, Wellington.
As with the Rational Method, the rainfall duration
must be determined by an empirical time of concentration
formula. The shape factor is a function of the catchment
area and length. The development of the method is discussed
by Campbetl (1959). When first introduced in 1953 this
method met an urgent need for a standard procedure for
flood estimation for ungauged catchments. Its value was
greatly enhanced by the publication of a probability
analysis of high intensity rainfalls (Robertson 1963).
1.3.2 Un¡t hydrograph methods
The unit hydrograph method developed in the 1930's has
become a widely used hydrological tool. The unit
hydrograph (UH) is the flow record from a saturated catchment
when a unit of rainfall falls uniformly for unit time.
As part of each storm is required to saturate the soil, the
UH represents only the "quickflow".
The quickflow from a rainfall excess of various amounts
over a succession of time units is calculated by superposition
of the set of unit hydrographs that correspond to the
rainfall excess. Thus the catchment is assumed to respond
linearly, in that runoff from a particular portion of storm
rainfall is unaffected by concurrent runoff from other portions
of the storm. These assumptions have been tested in
numetous studies and for small and medium sized catchments
have been found adequate for most engineering
design purposes. With a UH determined from a number of
storms and for average ratios of excess to total rainfall,
design floods for a catchment can be estimated from design
storms of the same probability. An important advantage of
this versatile method over those described previously is that
the shape of the flood hydrograph is calculated, and not
merely the peak rate of flow; this is of importance in
routing studies, in drainage design and in other situations
where it is necessary to know the length of time the water
level is above a particular stage. Possibly the main limitation
of the method is the subjectivity in determining the
volume and distribution of the rainfall excess. Where the
lack of flow records prevent the derivation of the UH, procedures
have been developed for synthesising typical UH
curves by relating characteristics of the hydrograph shape
to catchment characteristics. These procedures include the
well-known Snyder method and the US Soil Conservation
Service dimensionless hydrograph (Linsley et al. 1975),
These methods have been used successfully within two
regions of similar hydrological characteristics (Hoffmeister
1976). Also the Snyder method gave satisfactory results for
ungauged tributaries for the Waikato and Clutha Rivers
(Jowett and Thompson 1977), although Coulter (1961)
queries the wide applicability of the methods.
A guide to the order of loss rates that should be used is
given by Pilgrim (1966), who summarised published loss
rate information in New Zealand,. As most loss rates were
low (5090 of loss rates were less than 2.5 mm/hr and 8090
were less than 5.1 mm/hr), it was concluded that the inaccuracies
in transferring these values from one region to
another should cause only very small errors in design
floods. Nevertheless, more work is needed on loss rate
estimation in New Zealand as loss rates are important in
situations where flow forecasts are required. For tributaries
in the Motueka catchment Beable (1976) found loss rates to
be related to antecedent wetness, storm intensity and the
portion of catchment in exotic forestry.
1.3.3 Simulation methods
Under this heading is grouped a variety of methods for
representing catchment response to precipitation. Cat-
Water & soil technical publication no. 20 (1982)

chments are simulated with "models" that are simplified
representations of complex real-world systems. Models can
be (a) physical, (b) analogue, or (c) mathematical.
Mathematical models represent the behaviour of a catchment
by a set of equations and logical statements expressing
relationships between hydrological variables and model
parameters, with an input of precipitation and other
climatic nneasurementq and an output of stream discharge.
Such models can be classified as: "lumped" or
"distributed" depending upon whether variations in processes
over the catchment are considered; "time variant"
or "time-invariant" depending upon whether variations in
time of the model are considered; "stochastic" or "deterministic"
depending on whether probabilistic notions are
included; and "conceptual" or "empirical" depending on
the structuring of the model.
Extensive reviews of these models are given by Clarke
(1973) and Chapman and Dunin (1975). One use of such
models is the extension of a record of streamflows given a
record of precipitation. At present the model parameters
are usually estimated by fitting a predicted output
hydrograph to an observed output hydrograph over a
period of concurrent rainfall and flow records. Future
developments are aimed at enabling the estimation of
model parameters from observed physical characteristics of
the catchment without the need for a period of observed
flow record for model calibration.
1.3.4 Regional flood frequency methods
Regional flood frequency methods have been applied
widely, for example in North America (Thomas and Benson
1970), in'the British Isles (NERC 1975), and in
Malaysia (Heiler and Chew 1974). The index flood approach
used in this study averages the chance sampling
variation in flood frequency in a region, while preserving
the variation due to differences in catchment
characteristics. Development of the method involves:
(Ð collecting annual maxima for a number of flow stations
in the area thought to be homogenous;
(ü) drawing frequency-magnitude curves for each station
(Qr/Qvs T);
(iii¡ drawing a frequency-magnitude curve giving a
general Q1/Qvs T relationship for use in the region;
(iv) obtaining a regression relationship to estimate the
mean annua.l (or index) flood Qfrom measurable catchment
and climatic Parameters.
The regression relationship can- then be applied at
ungauged locations to estimate Q. Knowing Q
' the
regional frequenc¡' curves (iii) can be applied to determine
Q1 for a specified return period T. This method is one way
of extending a data base from a number of sites to cover a
region. Design flood estimates have to be made for many
more sites than can ever be gauged. This is justification for
developing the method in New Zealand, where it should be
noted that no quantitative information is available on the
accuracy of currently used empirical methods. It has not
previously been applied on a New Zealand-wide basis. It
has the advantage that it is based directly on flood records
whereas empirical and unit hydrograph methods rely on the
transformation of rainfall into runoff'
With the quantity of new data available by the middle of
the 1970's it was c,cnsidered feasible to develop the regional
flood frequency method. Regional inferences about flood
frequencies were made to provide a design flood estimation
method for catchments having little or no recorded data.
The frequency dirstribution which is most generally applicable
to the annual maxima series has been determined.
the first step was to assemble and check records of annual
ma¡

Water & soil technical publication no. 20 (1982)

2 Gollection of Data
2.1 Climate of New Zealand
The climate and rainfall patterns are strongly influenced
by the location and geography of the country.
A useful summarv is given in the New Zealand Year
Book (1978). In particular the chain of mountains extending
from south-west to north-east through the length of
the country is a barrier to prevailing moist westerly winds.
The effect is to produce much sharper climatic contrasts
from west to east than in the north-south direction. The
summary also indicates typical weather patterns that lead
to heavy rain.
2.2 Selection of catchments
Details of the criteria for choosing the catchments used
in the two sections of the study are given in Chapters 3 and
4 respectively. Initially all available annual maxima from
rural catchments with four years record and with flows
largely free from the effects of impoundments were considered.
Catchment areas were required to be greater than
0,1 km', but more restrictive ranges for area were imposed
later (See Chapters 3 and 4).
Lake inflows are the sum of flows from a number of
small catchments that contribute to the lake. Because of the
lesser channel routing effects in small catchments, the summed
instantaneous peak inflow may differ from the peak
flow from a single catchment of the same area subject to
the same storm. Although Gilbert (1978) describes a data
processing technique that ensures that lake inflows
calculated from level and outflow records have realistic
values, his work was not available at the time that the
criteria for data selection were determined. Lake inflows
were not used because the necessary calculation was believed
prone to error. However, recent work on the data
calculated by Gilbert's method shows that it conforms to
the same regional pattern as river flow data.
2.3 Sources of data
Although earlier developments were promising, the recent
progress in New Zealand in revising and developing
flood estimation methods outlined above has been disappointing
in comparison with other countries. Some of the
iag can be attributed to a lack of suitable data. Recognition
of the lack of data led to the implementation of the
Representative Basin programme under which more than
70 flow gauging stations were established with digital
recorders in the 1960's and'early 1970's. These stations,
together with improved instru
rs,
have recorded large quantities
ata
are available from files of the
ent
Data) hydrological archiving system which has been
developed by the Ministry of Works and Development
(MWD).
Inspection of the data held in this system (Figure 2'l)
showi that relatively few records were available before
1950, and that after 195ó an extremely rapid increase occured
in numbers of records a four-fold increase occurred
over the decade 1960-70. More than 400 records were
-
available from TIDEDA in 1978; many more were not
entered into
of
recorders ope
an
MWD report
i9d
ln-
of recording,
dicates whether the data are held in the TIDEDA system.
With approximatel'y 700 water level recorders on lakes and
rivers listed in this index, inadequate flow data should not
constrain regional hydrological analyses as it has in the
past.
Annual series da:a were collected from MWD and catchment
authority ftow stations. At the time of data collection,
comments were obtained on the accuracy of the data
and on the nature and conditions of the catchments from
the people in chargr: of the streamflow data processing, and
their advice was hr:eded in the acceptance or rejection of
data.
Where streamflow information was stored on the
MWD's TIDEDA system, plots of the streamflow were obtained.
Each plot vvas then scrutinised for the reliability of
the streamflow record before the annual flood peaks were
extracted from the record.
2.4 Oualfty of the data
The standards o I accuracy of data will undoubtedly vary
considerably front one catchment to another. Records
from a number of smaller catchments monitored at fixed
control structures may be expected to be of good standard
of accuracy for all flow conditions. For larger catchments
where the control lLs a natural river channel section, the accuracy
of estimat() of annual maxima will depend on the
stability of the cross-section, the frequency of gauging, the
range of flows overr which gaugings have been carried out,
and the general standards to which the recorder is
operated. Even if a good record has been maintained, conversion
of a recor,l of water levels into discharge requires
maintenance of a rating curve. In cases where the river has
large sediment loa.ds this is a difficult task. Judgement is
needed to decide how to extrapolate a rating curve, often
defined only for rredium or low flows, into a high flow
regime. Although greater confidence can be placed in
rating curves which include some flood gaugings, such
gaugings are not zrlways available.
Although Ibbitt (1979) describes a data processing
technique that ensures extrapolation of ratings to flood
stage is not upset by channel changes, this technique was
not the general practice when the flood data were assembled.
The inconsistency in flood flow ratings on the Rakaia
River prior to lbbitt's work (and illustrated in Fig' 5 in his
paper) are presumrably typical of the hydrometric practice
used to derive all the flood estimates used.
2.5 Historical information
Where possible. historical information was collected for
those flow stations with annual series data. Information on
historical floods, occurring both inside and outside the
period of continuous record, was obtained from: MWD,
õatchment authorities; reports; and from the publication
"Floods in New Zl,ealand l92O-53" (SCRCC 1957). The information
consisted of an estimate of the historical flood
peak together witlh the period of time over which the peak
was known to be the largest, second largest, etc. Advice on
the authenticity o1i many of the earlier historical flood peak
estimates was sought from the relevant data collection
agencies. The methods by which this additional informati,on
was used in the frequency analysis are described in
Chapter 3.
Water & soil technical publication no. 20 (1982)
ll

Doto ovoiloble on
TIDEDA
Figure 2'1 Number of water level recorder stetions
Water in & New soil technical Zealand and publication time d¡str¡bution no. 20 (1982) of water level data filed on TIDEDA.
l2

3. Regional flood frequency analysis
3.1 Flood frequencY method
3.1.1 General
Frequency analysis is a method of inferring the magnitude
of a design event from a given sample of recorded
events. The method is statistical and involves the fitting of a
frequency distribution to a sample of recorded events. The
resulting frequency curve is then usually extrapolated in
order to estimate the design event. In the case of a frequency
analysis of floods, the sample consists of flood
peaks taken from a streamflow record. The sample may
also contain some historical flood peaks, if this type of information
is available. Provided the streamflow record
from which the sample is taken is sufficiently long, flood
frequency analysis is generally regarded as the most accurate
method of estimating a design flood peak.
A flood frequency curve may be used for a catchment
where there is little or no streamflow record by a regional
flood frequency analysis procedure. Inherent in such a procedure
is the concept of a flood frequency region, i.e., in a
region which is reasonably homogeneous in terms of climate,
topography and soil characteristics and within which
catchments display similar flood frequency properties.
The regional analysis method employed in this study is of
the Index-Flood type, pioneered by the US Geological Survey
(Dalrymple 1960) and used by NERC (1975); it averages
the chance sampling variation in individual streamflow records
for a region, while preserving the variation due to differences
in catchment and climatic variables. An essential
part of the method involves the combining of the flood
peak data for a region to produce an average or regional
flood frequency curve, This regional curve is assumed to be
generally applicable to catchments in the region and may be
applied to both gauged and ungauged catchments. Because
the regional curve is based on a number of records from the
region, it provides a more reliable basis for extrapolation to
estimate a design flood peak than an individual frequency
curve fitted to a relatively short record.
Several frequency distributions have been proposed for
flood frequency analysis, but no single distribution has
been universally accepted. The fitting of a distribution may
be done either graphically, i.e., by fitting a curve by eye to
the plotted data sample and then extrapolating that curve to
estimate the design flood, or analytically, i.e., by estimating
the distribution's parameters from statistical characteristics
of the data sample. The anal¡ical approach, involving the
General Extreme Value distribution, was used in this study.
3.1.2 Terminology
A fundamental concept in flood frequency analysis is
that of a statistical population. The population is made up
of flood peak items, where each occurs in a separate partition
in time of the streamflolv at a site. These partitions are
Ù c.
ô
x
\
E
ë
l!
or
f(x)
= dF(x)
dx
F(x) = ¡x-f(x)dx
where, by definition
F(-) : Il- f(x)dx = t
Characteristics of the two functions, and the relationship
between them, are illustrated in Figure 3.1 using
the well-known Normal distribution. As shown in
Figure 3.1, F(x), the df, is the probability of a variate
value (x, in Figure 3.1) not being equalled or exceeded'
It may be expressed generally as
F(x) : P(Xsx) 33
P(xsxJ =/j'lt'lo-
Vor¡ole x
Port (o)
partitions in the total population. The variable value of a
hood peak in the flood record is called a random variable
or variate x.
The probability distribution of the variate x may be described
by either:
(i) f(x), its probability density function (pdf), which gives
the probability or relative frequency of occurrence of
x; or
(ii) F(x), the corresponding cumulative or distribution
function (df).
Vor¡ole r
Port (bl
P(xs xt)
Flguro 3.1 Charaster¡st¡cs of the pdf (Part al and the
The two functions are related bY
df (Part b) using a Normal distr¡bution.
Water & soil technical publication no. 20 (1982)
l3

P=45
O= 15
x4
(l)
'=
o
o
t.25 2'.O ¡b zs sb loo rooo T
-z.o -t'o 2.O 3.O
o.f o.3 0.5 0.7 0.9 0.95 o.9986
YH
F(x)
Figure 3.2 The plot of the df in Fig. 3.1 as a function of its ¡educed variate,
F(x) =l-P(X>x)
34
where P(
ote the probability of
non-exce
respectively.
Allied with
dence is the notion of
recurrence interval or return period, which is the reciprocal
of the probability of exceedence in a time unit. For instance,
if a flood peak is exceeded on average 20 times in
every 100 years, it has a return period of 5 years, or a probability
of exceedence in any one year of 0.20. Thus
P(X>x) = I T
which, from Equation
F(x) = I
3.4, gives
_l
T
whereT = returnperiod.
The curvatu
35
36
and the reliability of the extrapolation when the fitted frequency
line is straight rather than curved. A straight line
for the df can be obtained by rescaling the F(x) axiJ with a
on the F(x) axis, using the relationship between y and F(x)
and Equations 3.3-3.6. In this way different probability
papers, e.g., Normal and Gumbel, can be constructed to
produce straight line plots of their corresponding distribution
functions. Figure 3.2 illustrates the use of a reduced
yariate (y¡) for the Normal distribution shown in Figure
3.1. In accordance with convention, Figure 3.1 has been realigned
in Figure 3.2, so that the variate scale is now on the
ordinate and the probability and reduced variate scales are
on the abscissa; future mention of frequency curves is with
reference to this type of plot. The actual application of a reduced
variate is explained fully in section 3.1.3 with reference
to the Gumbel distribution.
typical ofthat Despite the use of a reduced variate, a straight line will
for a Normal
are plotted to not give a good fit when the data sample does not conform
natural scales.
curvature for, to the assumed distribution. However, it may still be possible
to obtain a good fit with a straight line by first trans-
when fitting ã
sferred to as a
relative frequency or simply a frequency distribution) to a forming the data sample. The most common transformation
is the changing of each sample item to its logarithm.
data sample, it is easier to visually assess the goodness-of-fit
Water & soil technical publication no. 20 (1982)
l4

3.1.3 General extreme value distribution
Of the frequency distributions used in flood hydrology,
many belong to either the Gamma distribution family or
the General Extreme Value (GEV) distribution. In this
study the GEV distribution is used for fitting the regional
data. This choice was supported by tests in which several
distributions were fitted to flood peak samples. The distributions,
the tests, and the results are described in Appendix
A.
Although the GEV was found to give a good fit to the regional
data, it appeared from the tests that the log-Pearson
Type 3 (LP3) distribution (also known as the three-parameter
log-Gamma distribution) may well have given an
equally good description ofthe regional trend. Aspects that
influenced the choice in favour of the GEV distribution
were the following:
(i) In a comprehensive comparative examination of the
GEV and LP3 distributions, NERC (1975 pp. 135-60)
found that the GEV performed more consistently in
the various goodness-of-fit tests.
(ii) The GEV distribution had been found by NERC
(1975) to describe their empirically derived regional
curves "remarkably well".
(lii) The fact that the GEV distribution had already been
used by NERC (1975) enabled a direct comparison of
jresults between that study and this one.
(lv) The GEV distribution afforded the more tractable
solution e.g., there was no equation available for the
LP3 that is analogous to Equation 3.14, wherein the
three-parameter distribution is expressed in terms of
the reduced variate for its corresponding two-parameter
(in this case log-Normal) distribution.
The pdf for the GEV distribution may be written as
f(x) = _t tl -k(x- u)/a|rk-ts-{l-k(x-u)/a}r/k .....3.7
ct
where u : alocationparameter,
d: ascaleparameter,
k = ashapeparameter,
and the corresponding df is
F(x): s-{r-k(x-u)/ø}k
Like the Gamma distribution, the GEV distribution describes
a family of distributions, each member of which is
characterised by the value of the shape parameter, in this
case k. The GEV distribution may be divided into three
types of extreme value (EV) distribution depending on
whether k is equal to, less than, or greater than zero. The
three types, and the corresponding range for which the pdf
(Equation 3.7) is non-zero, are defined as follows:
(¡) if k = 0, the rlistribution is type I (EVl) and the pdf is
non-zero for x>0;
(¡i) if k < 0, the distribution is type 2 (Ev2) and the pdf is
non-zeroforu + S . * < *;
K
38
and EV3 is also known as Weibull. The three types are also
called Fisher-Tippett type I, type2, and type 3.
Since k = 0 for the EVI distribution, the distribution is
only a two-param€rter one and the pdf simplifies to
(Ð=å
exp [ - (x - u)/o - e-(x- u)/a¡ 39
while the df reducr:s to
F(x) : s¡t [-e-(t -u),za¡
If a reduced varÍate y is now introduced for the EVI distribution
such that
or
,, _ x-u
a
X:U+cry
then the df may be written as
and
F(x) = s-e-r
x: u +f,tr-r-url
Using Equation 3.14 it is possible to distinguish between
the three types of EV distribution by plotting them on an
x- y probability plot (see Figure 3.3), otherwise known as
Gumbel probability paper.
The EV2 has a lower bound but no upper bound; conversely
the EV3 has an upper bound and no lower bound,
while the EVI iS unbounded.
If required, return periods and associated probabilities
can be scaled on the abscissa axis in Figure 3.3 by recalling
from Equation 3.ór that
and by substituting for F(x) in Equation 3.13. This produces
T- I
l-
l-e-e-Y
Y: -rn ('- rn(t-å, )
310
3ll
3t2
313
which gives rise to the name of double exponential distribution
for EVl.
Because Equations 3.ll and 3.12 describe a linear relationship
between x and y, the df for the EVI distribution is
given as a straight line on an x - y plot.
The GEV distritrution may also be expressed in terms of
the reduced variate y by the following equation derived by
Jenkinson (1955)
F(x):l-l
T
314
315
316
(ili) if k > 0, the distribution is type 3 (EV3) and the pdf is
non-zerofor-æ

Êv2
( ko)
Reduced Voriote y
I'O
t1
50 too
ttl
5to20
, Return Period, yeors
Figure 3.3 Differentiation of the three types of extreme value d¡stribution.
I
200
Table 3.1 The relationship between y and T values for the EVI
distribution.
Equations similar to 3.15 and 3.16, but this time relating
y and the probability of exceedence, may be obtained by
substituting P(X > x), as given in Equation 3.5, into the two
equations. This results in
1.O1
2.OO
2.33
5
10
20
30
50
100
200
500
1000
- 1.53
0.37
o.58
1.50
2.25
2.97
3.38
3.90
4.60
5.29
6.21
6.91
-2.O
- 1.5
- 1.O
-0.5
o
o.5
1.O
1.5
2.O
2.5
3.0
3.5
4.O
4.5
5.0
5.5
6.0
6.5
7.O
1.OO
1.01
1.O7
1.24
1.58
2.20
3.25
5.OO
7.90
12.69
20.59
33.62
55.1 0
90.52
148.9
245.2
403.9
665.6
1 097
and
P(X>x) = I -6-e-I
y = -fn(- fn(l-P(x>x))) .....3.18
3. I .4 Sampling properties
317
The data sample, from which a flood frequency analysis
infers a design flood magnitude, must possess the following
properties if the analysis is to make the proper inferences
about the population's distribution.
Sufftcient Length The data sample should be sufficiently
long, i.e., it should contain a large number of items. Often
l0 annual flood peak items are considered sufficient (Neill
1973; Beard 1977), though even then the sample is of limited
use in design (Linsley et al, 1975) unless supplemented
with additiongl hydrological information, €.g., a correlation
with a longer streamflow record from a nearby station.
t6
Water & soil technical publication no. 20 (1982)

Nevertheless, data samples of about l0 years in length are
common and are often the only data available.
Completeness The data sample should be complete, i.e.,
it should be taken from a continuous streamflow record.
Gaps in the record do not matter provided it is certain that
the maximum flood peak in the corresponding time unit
was recorded. However, where flood peak sample items are
missing as a result of gaps in the record, the time units containing
the gaps shortid be only a small proportion of the
total sample length. And rather than concatenating the various
recorded sequences together, it is preferable instead to
omit altogether the streamflow record for the time units
with the gaps (e.g., omit whole years for an annual flood
peak sample) and to treat the sample as having a correspondingly
shorter length.
Homogeneity The sample should be homogeneous, i.e.,
all the items should have occurred under the same conditions.
Factors which.can affect the homogeneity of a sample
include: man's activity (e.g., construction of reservoirs,
land use changes, stopbanking, channel realignment, flow
regulation, and diversions); faulty records; and changes in
gauging control conditions that re-rating has not accounted
for. Only samples which represent relatively stable catchment
conditions should be used. The homogeneity of a
large sample may be checked by splitting the sample into
two parts and comparing the frequency curve fitted to each
(Beard 1974, 1977).
Rondomness The time unit must be long enough that each
flood peak item in the sample is from a different flood
event, so that it is reasonable to assume there is no serial
correlation between successive flood peak items.
Reliability The sample items taken from the streamflow
record should be reliable measurements or estimates' Measurement
errors are generally small in relation to the year-toyear
variance in the sample items and can therefore usually
be neglected. The errors that are of concern result from
large extrapolations of the stage-discharge rating curve and
from the existence of an unstable gauging control. These errors
reduce the reliability of the data sample and, consequently,
the reliability of the fitted frequency curve, and
thus a record needs to be checked for their presence.
Representativeness The data sample should be representative
of the long-term or population distribution of items.
Clearly this is difficult to assess because the population is
unknown. However, the representativeness of the sample
can be tested statistically if there is a long-term streamflow
record for a similar catchment nearby (McGuinness and
Brakensiek 1964). Where tests show conclusively that the
sample is unrepresentative on a long-term basis, there
*ould be no point in applying frequency analysis methods;
the resulting frequency curves would have little predictive
value.
3.1.5 Types of samp¡e
In general three types of flood sample may be identified.
Annual Series The most usual form of a data sample is
the annual series, which consists of the maximum flood
peak for each year of
Pling generally
produces items
However,
it is claimed that a d
sample is
that it may ignore some large flood peaks and emphasise
smaller ones.
Peaks Over a Threshold Series An alternative type of
sample is the partial duration series, which seeks to overcome
the disadvantage of the annual series by containing all
flood peaks above an arbitrarily chosen base level. Sample
items chosen in this way need to be checked much more
closely for serial correlation than an annual series, because
large floods often contain more than one peak above the
base level.
Historical Series l{istorical information on flood events is
often available. rùy'hen it is reliable it should be used in conjunction
with the data sample taken from the continuous
streamflow record. The resulting data sample is called a historical
series. The inclusion of historical information often
significantly increases the length of a sample, thereby improving
the reliabitity of the frequency analysis. Moreover,
the information herlps to fix the top end of the frequency
curve, the end in u¡hich there is generally most interest.
In this study the: basic data sample used was an annual
series, which consisted of the maximum instantaneous discharge
for each year of record; historical information was
also included where possible. The partial duration series
was not used, even though it contains more items than the
annual series for a given length of record. It was excluded
because its advantage over the annual series is only when
the design return period is less than l0 years (NERC 1975;
Chow 1964, pp.8-i!.2,23). Furthermore, there is no guarantee
that it is better than the annual series simply because it
contains more data. As has been pointed out by NERC
(1975, section 2.2.4 and section 2.1\ and by Cunnane
(1975), the dictum "more data, better estimates" is not universally
true, and in certain circumstances estimates from
an annual series can be more efficient statistically than
those from a partiial duration series taken from the same
record.
3.1.6 Plotting
The probability plot, i.e., the x-y plot of the sample
data, is an integral part of hydrological practice. Despite
the numerous statistical goodness-of-fit tests now available,
few engineers who have to make decisions which are based
on the analytical fitting of theoretical distributions to sample
data would do so without first inspecting the fit of the
frequency curve on a probability plot.
In order to construct a probability plot, it is necessary to
know the return period or plotting position of each sample
item. Various fonnulae are available for calculating plotting
positions, witlh the following one the Weibull form-
-
ula
- being the nrost popular: 319
T -N+l rP - __
i
where Tp
and i
Water & soil technical publication no. 20 (1982)
N
the return period plotting position of a
fJood peak, in years;
the length of record in years (e.9., the
number of annual peaks for an annual
sr:ries);
= the rank of the flood peak in the series
(r:.g., I for the largest and N for the smal-
Iest of an annual series).
The formula has gained wide acceptance, largely because
of its simplicity and the fact that it gives results one would
intuitively expect. For example, the largest peak in an annual
series has a c,alculated plotting position only one year
greater than the length of record. This is consistent with
Gumbel's (1943) reasoning that the largest item in a sample
of N items should not have a return period significantly
greater than N, However, there is statistical evidence
against such an inl.uitive line of thought. For example, Cunnane
(1978), in a comprehensive review of plotting positions,
has shown statistically that for samples of size N belonging
to the EVI distribution, the largest item in the sample
has a return ¡reriod in the parent population of about
1.8N. In fact NEIìC (1915, p.67) and Cunnane have made
the point that the Weibull formula gives biased plotting
positions, which, on average, leads to an over-estimation of
flood peaks for high return periods.
Cunnane emphrasised the need to distinguish between the
plotting position of a sample item and that item's actual ret7

turn period. A plotting position formula merely gives the
position at which the item should be plotted in order to
assess the goodness-of-fit of the frequency distribution.
The actual return period of the item should be inferred
from the fitted distribution.
TP N + 0.12
i-0.4
Equation 3.20 also gives a reasonable approximation of
the unbiased plotting positions for a GEV distribution displaying
small or moderate curvature. It was therefore used
in this study for the calculation of plotting positions for the
methods involving EV distributions. It is possible to calculate
exact plotting positions for the EVI distribution for
small values of N but in practice, for N ) 35, the calculation
is overwhelmed by ro
a
,N
" a' iD=, 321
320
S).
(section
where Q¡ an individual annual flood peak, and
N the length, in years, of the annual series.
A dimensionless probability plot was then obtained for
The annual flood
3.2.1) for each flow s ¡sionless
form by dividing through by the corresponding mean annual
flood Q, defined as the arithmetic mean of the annual
series. Thus
mean annual flood Q standardises the series, permitting a
direct comparison of the plot of one series with anothèr.
Significant differences between plots are interpreted to
mean that the corresponding ftow stations belong to different
flood frequency regions.
volved, namely whether
(D the historical floods occurred outside the annual series;
or
(ii) tne historical floods occurred inside the annual series.
Dealing first with the type (i) series, consider an annual
period of J years,
to have occurred,
seri
dur
givi
fN+Jyears.In
this
nnual seiies were
based on a record length of N years, as before, while the
plotting positions of the historical floods were based on the
th of N + J years. Hence, for exorical
flood had a return period plotby
TP :(N + J) + 0.12 =
i-o.4
(N+J) + 0.t2 322
0.56
For the type (ii) series, consider the largest flood peak in
the annual series, of length N years, which also is known to
be the largest over a longer period of N + J years. Here the
t8
plotting position of the largest peak was based on the length
of the historical series N + J years, giving a return period
as indicated by Equation 3.22. The other flood peaks in the
annual series were then treated as the 2nd, 3rd largest etc. in
N years.
In the special case where there were two historical floods,
one outside and one inside the annual series of length N
years, the plotting positions of these two floods were based
on N + J years. Again the ordinary annual flood peaks
were considered as the 2nd, 3rd largest etc. in N years.
3. 1.7 Computer programs
In this study flood frequency analyses were performed
analytically using a computer program called FRAN
(Maguiness et al. in prep.). The methods included in the
program are outlined in Appendix A. Another program
called FRANCES (Appendix A) was developed ro analyse
the historical series data, which typically comprised an annual
series and an additional period of unknown record in
which one or more large, notable, and hence historical
floods, occurred. The program FRANCES performs a frequency
analysis of a censored sample, which may be defined
as a sample which contains unknown flood peaks that
all lie on one side of a given threshold value or censoring
point. An historical series may often be regarded as a censored
sample, where the unknown peaks are those which
occurred outside the annual series and which were less than
the known historical flood peaks. In using the program, it
is necessary to specify the historical flood peaks and to
assume that none of the unknown peaks exceeded the censoring
point, which must be set at a value less than the historical
peaks.
same method.
3.2 Flood frequency data
3.2.1 Data collect¡on
The collection of annual series data was restricted to
thosè flow stations which satisfied the following conditions:
(i) the catchment land use had not changed significantly
over the period of record;
(ii) the annual flood peaks were not substantially regulated
or affected by impoundments, swamps or diversions
within the catchment;
(iii) there were eight or more annual flood peaks available;
(iv) when historicat flood peak information was available,
there were also at least five annual flood peaks;
(v) the catchment was rural, or predominantly so;
(vl) the catchment area was greater than 20 kmr.
The first two conditions are consistent with the normal
requirements for data samples (section 3.1.4). The third
condition of only 8 or more years of record is slightly less
than the l0 years that is generally recommended as the
minimum sample length required for a typical flood frequency
analysis. However, this study was concerned, not so
much with flood frequency analyses for individual stations,
as with the derivation of regional curves from mass plots of
all the data for the regions (section 3.1.5). The reduction in
this study of the minimum sample length to 8 years allowed
the data for an extra 25 ftow stations to be used. It appeared
that these extra data would reinforce the definition
of the lower end of the regional curves.
The fourth condition, specifying five or more annual
flood peaks, was needed so that the mean annual flood Q
could be calculated, thus permitting the station,s historical
peaks Q to be expressed in the form of Q/Q and included
in the mass data plot for the region. Unless there were eight
Water & soil technical publication no. 20 (1982)

or more annual peaks, however, the annual peaks themselves
were not considered for the mass plot.
Condition (v) was necessary because the flood estimation
method sought was intended for rural catchments, not urban
ones.
Condition (vi) was imposed in the belief that flood frequency
characteristics of the very small and the larger
catchments would be markedly different. It was anticipated
that the effect of catchment storage in dampening the flood
hydrograph would be less in the very small catchments,
producing a steeper frequency curve of Q/Q than that for a
laiger catchment with the same rainfall excess. An area of
20 kmt was chosen as the lower limit on the size of a catchment.
It was later found, however, that catchments of
smaller size could have been included in some of the regions
(section 3.5.6).
An exception to the lower limit of 20 km'z was made for
the Northland-Auckland area. In this part of the country
there are relatively few large catchments, and without a relaxation
on the minimum catchment size any flood estimation
method would have only limited application. Moreover,
the presence of swamps had caused the rejection of a
number of annual series samples for flow stations in the
area. Therefore, to ensure that a reasonable amount of
flood peak data was obtained for the area and to enhance
the practicability of the resultant flood estimation method,
the lower limit on catchment size was reduced in the Northland-Auckland
area to 2 km'.
The data samples collected were plotted on Gumbel
probability paper and, after checks were made of their repiesentativeness
(section 3.2.2), samples for 152 stations
were finally accepted for use. For 148 of these stations
-
96 in the North Island and 52 in the South Island
-
the annual
series was eight years or longer; the remaining four stations
had historical information and an annual series of between
fltve and seven years in length. Five of the stations
were later omitted for the derivation of the regional curves
(see Table 3.2 and Appendix B). The location of all the staiions,
and their associated catchments, are shown for the
North and the South Islands in Figures 3.4 and 3.5, respectively.
Information on the stations is listed in Table 3.2'
grouped according to the regions into which the stations
were initially classified (section 3.3.1). The annual flood
peak data for the stations, statistics of the data, and comments
on the data and the catchments are summarised in
Appendix B, again according to the initial regional classification.
Attempts to extend short records by correlation
with adjacent longer records for a sample of stations in the
northern half of the South Island were unsuccessful and the
approach was not Pursued.
3.2.2 Minimum record length and outliers
ferent distribution'
on the use of an outlier are given by Irish and Ashkanasy
are as follows:
Water & soil technical publication no. 20 (1982)
(i) lf 5

'o ,l\,
I
zl
l-
I
Water & soil technical publication no. 20 (1982)

l'
cooxi:
i-
i - --l- ii
'___-T---
ô¡
sì
c
o
6
ø
ì
-9
It c66
E 5o
al,
ro
Gt
a¡
-É ¡t
I
I
---
ri
| _,+ --
\
\
t
Water & soil technical publication no. 20 (1982)

Table 3.2 Flow stat¡ons used.
SITE NO.
FLOW STÀTION
CÀTCHME{T ÀREÀ (KN2)
NO. ANNUÀI, (ÀND
HISTORICÀI) FI¡OD PEÀI(S
NORTHERN NORTH
REGTOIV
3506 Maungaparerua Rl-ver at Tyrees Ford
3819 Waiharakeke River at will@ Bank
49OI Ngunguru River at Dugmorers Rock
5809 Waiarohia River at RusselL Road
8501 wairoa River at !{eir
9101 waitoa River at [ihakahoro Bridge
9108 Piako Rj-ver at whalahoro Road
9203 waihou River at Puke Brjdge
9204 ohinemuri River at criærion Bridge
9213 Ohinenui River at KarangahåÌe
9223 Waihou River at Shaftesbuly
930I Kauaeræga River at Snithrs
14627 Waiari River at Muttons
43803 Papakura River at S.H. Bridge
45702 waiwhiu River at Done shadow
4661I Kaihu River at corge
46618 Megal(ahia River at corge
46625 Hikurangi River at Kæ-Hikurangi Bridge
46632 Whakapara River at S.H. Bridge
46660 Puketurua River at PuketiÈoi
47527 Opahi River at Pond
Ib.
NORTH ISLAND WEST' COAST REGTON
33IOl Whangaehu River at Kauangaroa
33103 llhangaehu River at S.H. 3 Bridge
33107 Whangaehu River at Karioi
33111 Mangawhero River at Ore Ore
33114 Waitangi River at Tangiwai
33U5 l.,langaetoroa River at School
33II7 ¡{akotuku River at s.H. 49À Bridge
33301 fdanganui River at paetawa
33302 Wanganui River at Te Maire
33309 f.,fanganui-o-te-ao at Àshworth
33313 Ohura River at Tokori.m
33316 Ongarue River at Taringmutu
33320 WhakaIEIÉ River at Foot¡ridge
33338 l.langanui River at Matapuna
3600I Punehu River at pihila *
39501 Waitara River at Tarata
39504 ¡,tanganui River at Tariki F.oad
43433 WaiIÞ River at VthaÈawhata
43435 WaipalÞ River at Ngarona Road
LO43427 Mangakino River at Dillonrs Road
1043461 longariro River at Upper Dan
1043466 Vlaihohonu River at Desert Road
Lc.
MANAI,/A1I.'-RANîITIKEI RE1ION
31903 Otaki River at hlapaka
32502 Manawatu River at Fitzherbert Bridge
32503 Manawatu River at Weber Road
32514 Oroua River at Almadale
32526 Mangahao River at Ballance
32529 lirawea Rive! at Ngaturi
3253I t4angatainoka River at Suspension Bridge
32563 Oroua River at Kawa Idool
32576 pohangina River at Mais Reach
3270L Rangitikei River at Kåkariki
32702 Rangitikei River at Manqaweka
32708 Rangitikei River at Springvale
32723 Maungaraupi River at porewa Road *
32732 Moawhango River at Waiouru
32735 Rangitawa River at Halcombe
32739 Tutaenui River at Hmond Street
Id.
SOUTHERN NQRTE ISLAND REGION
292OL Ru4ahanga River at wardells
29202 Ruanahanga River at Waihenga
29224 Waj-ohine River aÈ Gorge
29231 Taueru River at Te Weraiti
29242 Atíw}lakatu River at Mt Holdsworth Road
29244 Whangaehu River at waihi
29808 Hutt River at Kaitoke
29818 HuÈt River at BirchviLLe
2. BAY OF P¡NNTY REGTON
11. I
229
L2.5
L6.2
L2.7
433
528
1606
308
287
984
L22
69.9
57
s.03
tt6
246
I89
L62
2.4e
r0.6
t9t7
I968
492
539
63.5
33.2
20. I
6643
22I2
332
668
1075
184
97L
29.5
725
80
2926
r37
373
L74
88
301
3916
713
3L2
266
734
452
570
4'11
3595
27A7
583
25.6
245
62.4
47 -7
637
2340
ts3
373
38. B
36 .3
88. g
427
49
10
10
I
LO plus I hlstorical
I5
17 (includes I histolical)
L7(
19(
13 plus
L7
L2
18
historl.cal
t0
I
10
I plus I hlstorícal
17 (includes I hlstorical)
I
L7
L2
L2
I plus I historical
l0
13
9
ó
19
L4 plus I hÍstoricaL
t5
I5
14 plus I historical
L7
I plus I historical
I
I (includes I historica¡-)
L2
I3
T4
L7
L4
18 plus I historical
(includes !. historicaL plus l)
22
24
24
24
24 plus I historical
lo
I
5 plus 3 historical
(includes I historical pLus t)
l0
7 plus I historical
L7
I2
22
2L
22
I
9
9
9
6 plus I historical
L4610 Utuhina River at S.H. 5 Bridge
14614 KaiÈuna River at Te lltatai
14628 ¡,tangorewa River at Saunderrs Fam
15408 RangitaÍki Rjver at ¡turupara
33307 l,llanganui River at Headwaters
33324 Mangatepopo River at Ketetahi
33347 Wanganui River at Te porere
43472 Waiotapu River at Reporoa
1043419 Pokaiwhenua River at puketurua
1043428 Tahunaatara River at OhakurL Road
:043459 Tongariro River at TurÐgi
!043460 Tongariro River at puketarata
),
57
958
L79
II84
8I .3
3t
24.2
22A
448
2LO
772
495
Water & soil technical publication no. 20 (1982)
I6
20
L7
9
2l
9
(includes I historlcal)
II
I
IO
(includes I historíctl)
13
L2
(includea 2 historicat)
('

SITE NO.
FI¡W STÀîION
CÀTCHT.{ENT ÀNEÀ (KN2)
t¡o. ÀÀ¡NuÀf, (À¡¡D
HISTORICÀT,) FI¡OD PEÀKS
3. NORTH TST'AìID EAST COAST REGION
15410 Whirinaki River at Galatea
15432 Rangitaiki River at Kopuriki
I55II waima River at vlaimÐa Gorge
I55I4 Í¡hakatane River at whakatane
15536 wainana River at Ogilvies Bridge
15901 Waioeka River at Gorge cablesay
I97ol waipaoa Rive' at Kanakanaia Bridge
19?09 wharekopae River at Killarney
I97tI waingaronia River at Terrace
2I80I Mohaka River at RauPunga
21803 Moha](a River at Glenfalls
22802 E,sk River at WaiPunga Bridge
4. CEI\¡?RÀ¿ HAWKES BAY REG¡ON
23OOl lutaekuri River at PuketaPu
23002 Tutaekuri.River at Redclyffe
23102 Ngaruroro Rive! at Fernhill
23104 Ngaruroro River at KuriPaPango
23106 Taruarau River at TaihaPe Road
2320f Tukitui

e process of examining the simtrend
was repeated. Adjoining
d a similar trend were combined
together to form a flood frequency region. In this way ll
regions were built up.
In constructing the regions due recognition was taken of
the many factors that would influence the floods in the different
catchments. Attention was given to the climat€, topography
and soils of the catcr,ments, and the aim was to
have catchments with similar flood-producing characteristics
located in the same region. The construction was
guided by maps that showed countrywide climatic and physiographical
patterns, e.g., a Meteorological Service ãvei-
Survey topographical maps.
The ll flood frequency regions that were fîrst decided
upon are shown in Figures 3.6 and 3.7. Four of these regions,
Regions la-ld, were later combined into one (section
3.3.2). The list of stations within each region is given in
Table 3.2.
3.3.2 Development of reglonat flood frequency
cutves
The y values that were used in the regional plots were ob_
tained in the following ma¡ner:
(i) For flood records less than or equal to 35 years in
length, the y values were the exact ones for the unbiased
plotting positions for the EVI distribution and
they were taken from a table in NERC (1975, pp.g2_
3).
(¡i)
0.5 class intervals, and an average e/Q and y value was calculated
from the data points falling within each class. This
averaging process was the same procedure as that used by
NERC (1975) and it produced a smooth trend in the regional
data.
The GEV distribution, namely
In the second case no constraint was placed on the value for
k, so that in general a GEV fit was obtained. However, because
of the relatively small size of many of the data samples
used, and in view of the findings in the evaluation tests
(Appendix A) relating to small samples, the EVI fit was regarded
as the regional curve unless the GEV fit produced a
significant reduction (10 percent or more) in the sum of
squares.
It was not always practical, however, to fit Equation 3.14
to a regional set of average values. Because of the limited
amount of flood peak data available for some of the regions,
the averaging process sometimes produced an unrepresentative
or biased set of average values for a region,
where the average values for low class intervals of y were
based on many data points while for higher class intervals
they represented only one or two points. To reduce the possibility
of obtaining unrepresentative regional curves,
Equation 3.14 was only fitted to a s€t of average values
when:
(l) the total number of flood peaks for a region was
greater than lü); and
(ll) there was no more than one average value for the region
that was based on one data point.
When these criteria were not satisfied, the regional curve
was defined instead by fitting Equation 3.14 in the manner
described ea¡lier to all the plotted data for a region.
Except for the Bay of Plenty (see section 3.3.3), the regional
curves were obtained from the procedures outlined
above and are given in Figures 3.8-3.16. tilhere a regional
curve wÍrs dehned from a set of average values, the plot of
the curve fitted to these values is shown along with the corresponding
regional probability plot, which contains all the
flood peak data for the region. (The historical peaks in a regional
plot are indicated with circles and the corresponding
site numbers are given alongside). Where average valuei
were not used, only the regional plot with the regional curve
superimposed is shown.
The regional curves derived for the North Island West
Coast regions, i.e., Regions la-ld, are plotted together in
Figure 3.17. Although there are differences in the trends of
the data in the corresponding regional plots, it can be seen
from Figure 3.17 that the flrtting of the straight-line EVI
distribution to the data of each region masked these differences
in close agree_
ment.
seeme
the curveS, it
ction between
four regions
for the com-
. Vy'est Coast
region. Averages ofthe pooled data were calculated for the
x=Q/Q
= u*9(l-e-tv¡
k
3t4
24
a :a
=U*oy 323
Support for pooling the data from several regions together
is given by Stevens and Lynn (lg8) who used three
statistical tests to analyse the variation amongst the regional
curves derived by NERC (1975). They concluded that the
curves for some regiôns of Great Britain, while not necessarily
identical, were certainly very similar. On these
grounds they pooled the data for the regions with similar
curves to obtain more stable estimates of floods at high return
periods. The data were pooled into two groups, one
for the fïve south-east regions of Great Britain and one for
the five north-west regions. A frequency curve was then fitted
to the data of each group and extended to the lüXÞyear
return period.
Water & soil technical publication no. 20 (1982)

I
Fþuru 3.6 North lsland flood frequency regions.
Water & soil technical publication no. 20 (1982)
25

Iì_
t_
I
I
I
I
I
I
I
t-.
I
I
tñ
I
LÓ.
I
t¡l
l\-'
LØC'
I
South lslând west Coast
l
_l
I
T.-
t-l-l
\
\
i
l
\-
\
\
\
\
Flguro 3.7 South lsland flood frequencV regions.
Water & soil technical publication no. 20 (1982)
26

NORTHERN
to
o
o
ñ'
Þ
o
.,¡'
c
e. !:r
NORTHERN
NEIUNN FERIOD ÍYEFRS)
N.I. BEGIONßL CUBVE
.50 2.25 3.00
REOUCEO Y VRFIRTE
¿. t! É rb zb rb so z's roo
RETUNN PEßIOO fYEÊNS)
, Fþure 3.8 Region la: the regional plot and curve.
27
Water & soil technical publication no. 20 (1982)

Þ
I"IEST COFST
0
o
I
E
6o
o
o
25 3,00
NEOUCEO Y VFñIRÎE
r.btl 23t Ë tô 20 30 so ?5 loo
REÍUNN PENIOO fIERñSI
NEST COFST N. I . BEG I ONÊL CUBVE
o
o
o
lo
g
o
6
o
i.so ¿."s i.oo
NEOUCEO Y VFNIßTE
É r'o zi s'o Eo ?-6 lôo
RETUNN FEN¡OO (TEFFSI
28
Figun 3.9 Region lb: the regional plot and curve.
Water & soil technical publication no. 20 (1982)

MßNRI,.¡RTU-RßNGITIKEI BEGIONIRL CURVE
o
a
";
o
";
o
Ð
"i
l@
G oo
";
o
I
BEOUCED 'I VRH I ßTE
5102030
RETUBN PEBIOD (YEHFs)
Flgurc 3.1O Region lc: the regional plot with the curvo superimposed.
Water & soil technical publication no. 20 (1982)
29

SOUTHEBN
REDUCEO Y VRBIßTE
NETURN PEBIOD (YEHNSI
o
SOUTHEBN N. I. BEGISNRL CUBVE
Þ
o
Þ
o
Þ
o
lø
@
o
è
o
t,50 2.?s i.oo
BEOUCED Y VFRIFTE
s rò ao 3b sb ;'s röo ãõo
RETUBN PEBIOO (YEFBS)
30
Fþuru 3.11 Region ld: the reg¡onal plot and curve.
Water & soil technical publication no. 20 (1982)

CORST
BEG I ONÊL
CUBVE
REOUCEO I VRBIRTE
l.ort 2.33 5 l0 20 30 50 .75 t00 200
BETUNN PEFIOD (IERHS)
Fþure 3.12a Region 3: the regional plot w¡th the curvo superimposed.
CENTBFL HRhIKES BßY BEGIONFL CUBVE
l.so 2.2s 00
FEOUCEO Y VRBIRTE
r.ótt 2'33 s to zo 30 so ?s lo0 ¿00
BETUBN PENIOO (YEFNS)
Fþur 3.12b Region 4: the regional plot with th€ curve superimposed.
Water & soil technical publication no. 20 (1982)
3l

SOUTH ISLFND HEST COFST I]ÊTR
èo
d'
o
I
.ü'
lct
o oè
o
b
.50 ¿.25 3.OO
NEDUCEO Y VFNIâTE
NETUNN FEBIOB (YERBs¡
Þ
SOUTH
ISLÊND 1,,IEST COÊST BEGIONRL CUBVE
Þ
o
è
o
IG
oo o
o
Þ
0
REOUCEO Y VFNIFTE
NETUNil PEN¡OO fYERBS¡
32
Fþurc 3.13 Region 5: the rog¡onal plot and curve.
Water & soil technical publication no. 20 (1982)

SOUTH
I SLRNT]
o
ê
Þ
Þ
Þ
lo
Go o
Þ
o
00 3.75 {,50 5.25
FEOUCEO Y VRNIFTE
l.otl ?,9t s ¡0 20 lo s0 75 100 200
BETUßN PEBIOO (IERFS¡
SOUTH ISLÊND EÊ5T COÊST REGIONßL CUßVE
.so 2.2s 3.00
REOUCEO I VßNIRTE
Ë l'o io !'o so ?3 róo
RE'TURN PEBIOO (YERNSI
F¡gur.3.14 Regbn 6: the regional plot and curve.
Water & soil technical publication no. 20 (1982)
33

SOUTH CÊNTERBURY DRTÊ
NEOUCEO Y VßFIFTE
l.ott 2,33 s ¡0 20 30 s0 7s 100 200
RETURN PEßIOO (YEÊNS}
o
SOUTH CÊNTERBI-JRY BEG I ONF]L CURVE
t
o
o
Þ
G'
oo
o
o
t
r.so 2.2s 3.00 3.75 q.so
NEDUCED Y VÊNIRTE
2.93 5 ¡0 20 30 50 7s 100
RETUBN PER¡OD (IEß85)
34
Flgure 3.15 Region 7: the regional plot and curve.
Water & soil technical publication no. 20 (1982)

OTFGO_SOUTHLÊND BEG I ONFL CUßVE
s0 -75 00
BEDUCEO Y VßBJßTE
00 q.50 s.zs
l.0ll 2.33 5 lo 20 30 s0 ?s
RETURN PEBIOO {YEßBSI
Flgure 3.16 Region 8: the regional plot with the curve superimposed.
N. I . I,'IE5T CORST BEG I ONRL CUBVES
r00 200
2.31
00 3.75 r¡.50
REOUCEO Y VFRINTE
10 20 J0
NETURN PENTOO --- (YERRS)
50 7ri 100 200
Flgure 3.17 Summary of the regional curves for Regions 1a-1d.
Water & soil technical publication no. 20 (1982)
35

COMB I NED
,,IE5T CORST DRTR
o
rt
€o
o
o
NEOUCEO Y VFBIRTE
?5 r¡.50 5.25
t-0¡¡ 2.93 s t0 zo 30 so ?'5 róo eú¡
BETIJñN PEBTOO (YEßñS¡
j
COMB I NED N. I . I^IEST COÊST ßEG I8NÊL CURVE
o
Þ
a;
o
ê
Þ
ø
rct
o
o
o
D
o
50 -'.75 1.50 2.25 3.00 3.75 r¡.50 5.25
SEDUCED Y VßNIRTE
t.oll 2.1! 5 t0 ¿0 !o 50 75 r00 200
NETUNN FEBIOO (IEflNsI
Figure 3.18 Region 1 the regional plot and curve.
Water & soil technical publication no. 20 (1982)
36

3.3.3 Bay of Plenty region
Missing from Figures 3.8 to 3.16 is the plot of the regional
curve for the Bay of Plenty region (Region 2). In defining
the average curve for this region it was found that
four large historical floods appeared to produce an unrealistically
high degree of upwards curvature at the top end of
the fitted curve. Fitting a curve to all the plotted data instead
of just the average values made very little difference.
Therefore in an effort to obtain a more realistic regional
curve, an extension method was employed (NERC 1975,
pp.l7t-2).
The method involved splitting the dimensionless flood
peak data for the region into three groups (Table 3.3a).
Each group contained the data for stations whose catchments
were not close neighbours, so that it could be assumed
that a group's sample items were statistically independent.
The largest four Q/Q values in each group, irrespective
of station, were then treated as the four largest
values in a random sample of size M, where M was the total
number of station years spanned by the data in a group,
and not simply the total number of flood peaks for the stations
in a group. Hence, where there was an historical series
containing a flood peak known to be the largest in N + J
years, the number of station years for this particular station .
was N * J years, the historical record length. In the special
case where the historical series did not contain the largest
historical peak in N + J years but, say, only the second or
third largest in that period, the number of station years was
not so straightforward and an equivalent length in years
had to be determined. The return period of the second or
third largest historical peak was calculated using the Gringorten
formula (Equation 3.20) and substituted back into
the formula, this time using a rank of one instead of two or
three as before. The value of N resulting from this back
substitution was taken as the equivalent length of station
years.
The number M varied from group to group, but an attempt
was made to keep it reasonably constant. Values for
y were calculated for the four largest Q/Q values in each
group by taking M as the record length and using the Gringorten
formula and Equation 3.16 (Table 3.3b). The 12
pairs of Q,zQ values and their corresponding y values, i.e.,
the four pairs from each ofthe three groups, were averaged
over the 0.5 class intervals of y (Table 3.3c), and the three
largest averages were plotted along with those obtained
from the original flood peak data. There is some statistical
dependence between the two types of average values, but it
was thought that, with M being fairly large for each group,
the dependence would be small. Finally the regional curve
was defined by fitting Equation 3.14 to the combined set of
original and new average values.
The probability plot of the regional data is shown in Figure
3.19 (the four historical flood peaks are indicated with
circles and the corresponding site numbers are given alongside).
Also shown is the regional curve that resulted from
fitting Equation 3.14 to the original and new average
values. The latter values are indicated with squares.
It was difficult to finalise the Bay of Plenty's southern
boundary line which, from the probability plots, appeared
to lie somewhere near the mountains in the volcanic plateau
area of the North Island. Besides the problems caused by
the geology and the uncertain Ìveather pattern in this area,
there were also complicatións arising from the Tongariro
Power Development Scheme which had altered the natural
flow of some of the rivers. While the chosen southern
boundary is reasonably consistent with the geology of the
area and with the trend in the probability plots for the stations
concerned, some further definition of the boundary
line may be necessary at some later stage.
The definition of the Bay of Plenty on its eastern boundary
posed a problem of a quite different nature. The probability
plots clearly indicated that the eastern boundary line
TaHe 3.3 Calculatk¡ns for extending the set of average values
for the Bay of Plenty region.
(a) Grouping of statio,ns
Group 1 Group 2 Group 3
Mangatepopo @
Ketetahi
t=8
Utuhina @
S.H. 5 Bridge
r=9
Tongariro @
Turangi
t=26
Waiotapu @
Reporoa
f=38
Wanganui @
Te Porere
l=10
Kaituna @
Te Matai
r=21
Tongariro @
Puketarata
t--26
Tahunaatara @
Ohakuri
t=12
Wanganui @
Headwaters
( = 11
Mangorewa @
Saunders Farm
f=9
Rangitaiki @
Murupara
t-_38
Pokaiwhenua @
Puketurua
¿ = 13
M=81 M=69 M=71
/ = the length in ye,ars spanned by the data for a station.
M = the total length of station years spanned by the data ¡n a
group.
(bl The maximum O/O and y values
Group 1 Group 2 Group 3
o/o o/o O/o y
2.870 4.972
2.464 3.941
2.044 3.440
1.746 3.104
2.649 4.811 2.994 4.840
2.462 3.780 2.261 3.809
2.008 3.277 1.993 3.306
1.944 2.940 1.960 2.969
(c) Classification and averages of the maximum O/O and y values.
y interval
4.5 - 5.O
4.O - 4.5
3.5 - 4.O
3.O - 3.5
2.5 - 3.O
Water & soil technical publication no. 20 (1982)
No. of values Average O/O Average y
3
3
4
2
2.84
2.40
1.95
1.95
4.87
3.84
2.28
2.96
should be near th€ Rangitaiki River, with the catchments
either side of the river displaying a noticeably different
flood frequency trend. Support for this difference in trend
can be found in the geology of the area. The area west of
the river is a pumice and rhyolite zone, whereas the area to
the east comprises sedimentary rocks, e.g., sandstones and
greywackes. The dividing line between the two geological
areas is abrupt and coincides almost exactly with the line of
the Rangitaiki River: The problem then was not so much
where to locate the boundary line, but in which region to
put the flow stations for the Rangitaiki River itself, since
the flow in the riverr represents the integral effect of the two
geological areas on the runoff process. However, the trends
in the probability plots for three stations on the river (i.e.,
sites 15408, 15410 and 15432) were consistent with the flood
frequency trend of one of the regions either side of the
river, and the bourrdary line was drawn such that each station
was included in the most appropriate region.
The same approach could not be applied to a fourth flow
station on the river at Te Teko (site 15412), which is downstream
of the othe¡ three stations. The trend of the Q/Q
probability plot for this station lay in between the trends exhibited
in the Bay of Plenty and North Island East Coast regional
plots. This was presumably because the peak flow at
the station contains very significant contributions from
37

BÊY OF PLENTY DRTF
o
o
o
NEOUCEO Y VRBIßTE
s r0 ¿0 30 50 7s r00
FETUFN PEHIOO (YEßRS)
BÊY ÚF PLENTY BEGIONÊL CUBVE
o
o
lo
o
Þ
Þ
è
t.so 2.25 3.00 3.75
NEOUCEO Y VRNIßTE
r.ô¡r 2.3! s ro ¿o !o 50 75 ¡oo 2oo
nETUBq FEnI00 tYERnS)
Flgure 3.19 Region 2: regional plot and curve.
Water & soil technical publication no. 20 (1982)
38

Tablo 3.4 Summary of the regional curve characteristics.
Region Regional Curve Ordinates Regnl. Parameter Values
for Eq. 3.14 or 3.23
O, sglO O¡/O O,o/õ Oro/O O.o/õ O,oo/O OrooiO
Regional Cuwe
Equation,OO =
NORTH ISI.AND
1. Combined N.l. West Coast 1.OO
2. Bay of Plenty 0.96
3. N.l. East Coast 1.OO
4. Central Hawke's Bay 1.OO
SOUTH ISI.AND
5. S.l. West Coast O.99
6. S.l. East Coast 1.OO
7. South Canterbury 1.OO
8. Otago-Southland O'98
1.30 1.55
1.31 1.62
1.43 1.78
1.49 1.89
1.22 1.41
1.31 1.56
1.52 1.95
1.33 1.62
1.78 2.09
1.96 2.46
2.12 2.56
2.27 2.77
1.59 1.82
1.80 2.12
2.39 2.94
1.89 2.25
2.32 2.55
2.87 3.33
2.89 3.21
3.14 3.51
1.99 2.16
2.35 2.58
3.44 3.91
2.51
0.804 0.330
0.762 0.325
0.726 0.469
0.696 0.s32
0.846 0.249
0.809 0.335
o.689 0.529
o.762 0.380
O.8O4 +O.33Oy
-O.142 1.53O+2.292exp
lO'142Y1
O.726 +0.469y
0.696 +O.532y
O.846 +0.249y
0.8O9 +o.335y
-O.O52 -9.545+10.234
exp (O.O52y)
0.762 +O.38Oy
both regions, and to have included it in either regional plot
\r/ould bias the resulting regional curve; down\ryards in the
case of the Bay of Plenty curve and upwards for the North
Island East Coast curve. The Te Teko station was therefore
omitted from the derivation of the regional curve for both
regions.
Clearly, in deciding which regional curve to use for
points on the Rangitaiki River system, consideration needs
to be given to such factors as which region contains the
greater proportion of the catchment area, and whether the
western or eastern part of the catchment contributes most
to the peak flows at the point in question (see also section
5.2\.
The number of stations near the eastern boundary of the
Bay of Plenty region permitted such a detailed examination
ofihe boundary line. In general, however, there were insufficient
stations to be able to do this' Most lines were subjectively
defined and they should be regarded as broad dividing
iines between regions. To define the regional boundarils
more precisely will require more flow stations with
more flood peak data.
3.3.4 Final rog¡onal curves
The final regional flood frequency curves that were derived
are summarised in Figure 3'20. In general' the curves
The excePtion is the
minimal amount of
gional curve Past 100
years, and the curve is tentative only.
The ordinates Q'¡/Q for the final regional curves are
listed in Table 3.4 for selected return periods. As well, the
the eastern South Island area identical to the annual flood
regions defined f,or estimating Q (section 4.5). Regional
plots correspondirng to the flood regions in the area were
constructed, but the data showed substantially greater variability
than was evident in the plots for the original flood
frequency regions, i.e., Regions 6, 7 and 8 in Figures 3'14-
3.16. Still pursuing the possibility of having consistent regions,
all of the flood peak data for the three flood frequency
regions were subsequently pooled together, forming
a combined region known as the Eastern South Island region.
The regional plot that was obtained for this area, and
the resulting regional curve, are shown in Figure 3'21. A
comparison of this plot with those for the original three
flood frequency regions (Figures 3.14-3.16) shows that the
variability in the data for the combined region is much
greater. This is borne out by the standard error equation
developed for the regional curve of the combined area
which gave a C¡ I'alue at the 100-year return period, for example,
that was 25 percent greater than that given by the
group equation (llable 3.9) for the original regions (see section
3.4.1). This greater variability was not surprising in
view of the range in the ordinates of the regional curves for
the three regions. For instance, at the lü)-year return period
the difference between the South Canterbury and South
Island East Coast regional curve ordinates is l.l8' or 50
percent of the ordinate for the latter curve. Because of this
iange, and the greater variability in the regional plot for the
combined area, tlhe curves for the three original regions offer
a more accurate estimate of Q/Q for sites in the area
and the three regions were therefore retained as the flood
frequency regions.
3.3.5 Consistent regions
For th
the resul
made of
3.3.6 Sub-reglons
It will be noted that two small areas in Figures 3.6 and 3.7
have been specially identifl¡ed as sub-regions. The first is
that area around Mt Egmont in the combined North Island
West Coast region (see Figure 3'6). Flood peak data were
available for onìly two stations in the area, although each
was associated u¡ith a representative basin. The catchment
for the station on the east of the mountain (site 39504,
Manganui River at Tariki Road) was included in the North
Island West Coast region after its flood peak data were
found to conform very well with the regional flood frequency
tr€nd. The second station (site 36001, Punehu River
at Pihama) was located on the southern side of the mountain.
Its flood peak data displayed distinct upwards curvature
on a probability plot, a trend markedly different from
the regional one,, Because it was uncertain whether this was
ase ofaPPlication of a real trend, or simply the result of using a short record
an examination was (eight years), the southern area of Mt Egmont was excluded
frequencY regions in from the North ltsland West Coast region' More flood peak
Water & soil technical publication no. 20 (1982)
39

NOBTH ISLRND ßEGIONÊL CUBVES
1.50 2.?S 3. OO
REDUCED Y VRBIßTE
2,33 sl02030
BETUBN FERIOO (YE8BS)
50 75 r00
Flgure 3.2Oa Summary of North lsland regional cury€s.
SOUTH iSLÊND REGIONÊL CURVES
1.50 2-25 3.(
BEOUCED Y VRBIFTE
s r'o ¿'o g'o
RETUNN PEBIOO IYERNS)
1t.50 5.2S
so 7s t00 200
4
Fþure 3.2Ob Summary of South lsland regional curves.
Water & soil technical publication no. 20 (1982)

EßSTEBN SÚUTH ISLÊND OÊTÊ
00 3.75 q.50
FEOUCEO I VFFIFTE
l.Oll ?,33 s t0 20 30 50 75 rO0
NETUFN FEFI OO f YERFS'I
EßSTEBN SOUTH ISLßND REGIONÊL CUBVE
o
1.50 2.25 3.00
BEOUCEO Y VRBIBTE
5r02030
NETUHN PEHIOO (IERBS)
q.50 5. ?5
s0 ?s r00 200
Figure 3,21 Eastern South lsland regional plot and curve.
Water & soil technical publication no. 20 (1982)
4l

data for this area are required before a decision can be
made whether to make the area a region in itself or to include
it in the surrounding region.
The second sub-region identified is the area south-west of
Nelson in the South Island West Coast region (see Figures
3.7 and 3.22). lt was of interest in that the flood peall data
for two flow stations (sites 57008 and 57101) in the area did
not conform at all to the regional flood frequency trend;
these stations were omitted from the derivation of the regional
curve. The non-conformity of the data was thought
to be due to the fact that the area is in a rain-shadow, caused
mainly by the Southern Alps to the west, and receives
significantly less rainfall than the other parts of the region.
These factors encouraged a detailed look at the flood frequency
behaviour in the whole area,
The flood peak data that were collected for the area according
to the criteria in sections 3.2.1 and 3.2.2,together
with extra data that did not meet these criteria but were
nevertheless thought to be of some use here, were pooled
together to form a probability plot for the area. All the data
used in the plot are summarised in Table 3.5, while the extra
data are listed in full in Appendix C.
The probability plot that was obtained for the Nelson
area, and the curve that was fitted to the plotted data, are
shown in Figure 3.23. Despite the inadequacies with the
data and the small number of flow stations used it would
seem, both from the trend in the probability plot and from
the large difference between the fitted curve and the South
Island West Coast regional curve (shown as the dashed line
in Figure 3.23), that there is some justification for treating
the area south-west of Nelson as a separate sub-region, and
not part of the surrounding region. A greater amount of re-
Iiable data is needed to confirm this point and to define the
area's own regional curve with confidence. In the meantime,
however, it is suggested that the regional curve for the
South Island East Coast region should be used for the area
rather than the one for the South Island West Coast region.
The former region is drier and has a steeper frequency
curve and hence is more in keeping with the Nelson area.
3.3.7 General¡sed flood frequency curves
From all the flood peak data assembled for this study,
two generalised flood frequency curves extending to high
return periods were developed. In recognition of the differences
in the characteristics of the regional curves for the
west and east of New Zealand, one generalised curve was
developed for the western areas (Regions I and 5) and one
for the eastern areas (Regions 2,3, 4,6, 7 and 8). The development
was based on the principle utilised by Stevens
and Lynn (1978) of pooling regional data together to obtain
more stable flood estimates for high return periods. With
the large base of pooled data for each generalised curve, it
was hoped that the curves could be extended to the 1000-
year return period with sufficient accuracy to be useful in
design.
These curves incorporated many of the historical flood
peaks that were excluded from the regional analyses under
Rule (lli) of section 3.2.2. ln general, this rule was invoked
in a regional analysis because a flood peak was an extreme
outlier and the available length of flood record at the station
concerned was insufficient for the computation of a
plausible return period for that flood peak. However, there
were good reasons for including here some of the previously
excluded historical peaks: the large base of data for
each curve, together with the use of the extension method,
would help to prevent these peaks from exerting undue bias
on the shape of the curves; and as the curves were to be extended
to the 1000-year return period, the flood peaks with
return periods approaching this limit should be used, where
possible.
All but four of the previously excluded extreme peaks
were considered suitable for the development of the generalised
curves, The remaining four peaks were truly extreme
events, and even tbe large bases of data associated with the
generalised curves were insufficient to enable realistic return
periods to be ascribed to them. Two of the peaks occurred
in the same storm in 1938 in the adjacent Mohaka
Table 3.6 Calculations for extending the sets of average values
for the generalised curves.
(a) The Maximum O/O and y values.
Western New Zealand
Group 1 Group 2 Group 3 Group 4
o/o
4.58 7.13
2.94 6.11
2.91 5.61
2.74 5.28
o/o
4.84 7.O7
2.62 6.O5
2.59 5.55
2.45 5.22
yo/OyO/Oy
M= 7OO 661 659
No. of Stat¡ons
: 23 15
Eastern New Zealand
2.99 7.O7 3.90 7.13
2.58 6.05 3.25 6.1 1
2.46 5.55 2.81 5.61
2.40 5.22 2.49 5.28
700
Group 1 Group 2 Group 3 Group 4
o/o o/o o/o o/o
3.12 6.68
2.87 5.65
2.74 5.15
2.54 4.42
4.31 6.68
4.06 5.66
3.65 5.1 6
3.55 4.83
4.62 6.69 3.85 6.83
3.82 5.66 3.75 5.80
2.99 5.17 3.53 5.31
2.A7 4.83 3.06 4.98
M= 444 448 450 517
No. of Stations
= 14
19
(bl Classification and averages of the maximum O/O and y values.
t5
t3
Table 3.5 Summary of flow stations in the Nelson a¡ea.
Site No. Flow Station Catchment No. Annual
Area (km'zl (and historical)
flood peaks
56901 Riwaka River at Moss Bush
57002 Motueka River at Baton Br.
57006 Wangapeka River at Swing Br.
57OOB Motueka River at Gorge
57009 Motueka River at Woodstock
571O1 Moutere River at Old House Rd.
571OG Stanleybrook River at Barkers
48
'1647
373
163
1750
60.7
81
10
18
I
9
8
10
7
y lnterval
Wefem NZ:
7.O - 7.5
6.5 - 7.0
6.0 - 6.5
5.5 - 6.0
5.0 - 5.5
Eaetem NZ:
6,5 - 7.O
6,0 - 6.5
5.5 - 6.0
5.0 - 5.5
4.5 - 5.O
No. of values Average O/O Average y
4
4
4
4
4
4
4
4
4.O8
2.85
2.69
2.52
3.98
3.63
3.23
3.O2
7.10
6.08
5.58
5.25
6.72
569
520
487
42
Water & soil technical publication no. 20 (1982)

7009
o
ELSON
57tO6
LOCALITY PLAN
Scole O 5 lO 15 20 25 km
Figwe 3.22 Some flow stations in the Nelson area.
generalised curves'
The development of each geleralised curve involved the
calculation of the average Q/Q and y values, for the 0'5
class intervals of y, from all the pooled data for the area
concerned. Additional average values were then obtained
using the same extension method as employed for the tsay
of Plenty regiorr (section 3.3.3). This time, however, four
groups of staticlns were considered fo-r each curve, with
each group again comprising all the Q/Q values for the stations
whose catchments were not close neighbours. A summary
of the foul largest Q/Q values for each group is given
in Table 3.6a. It will be noted from this table that the number
of stations rvithin each group and also M, the number
of station years spanned by the data in a group, were kept
reasonably constant. The four Q/Q values per group ìvere
treated as being the four largest in a sample of record length
M, and their corresponding y values were calculated accordingly
using the Gringorten formula (Equation 3'20)
and Equation 11.16. The resulting sixteen pairs of Q/Q
values for each curve and the corresponding y values, i.e.,
the four pairs fiom each of the four groups, were subsequently
averaged over the 0.5 class intervals of y (Table
3.6b). These new averages were later plotted on the same
probability plot as the original averages. Finally, Equation
Water & soil technical publication no. 20 (1982)
43

NELSON REGIONFL CURVE
BEOUCEO Y VRRIÊTE
FETUNN PEBIOO (YEHRS)
Figure 3.23 Mass probability plot and fitted curve for the Nelson a¡ea.
3.14 was fiued ro rhe combined set of original and new 3.4 FlOod ffequency acculacy
averages using the optimisation technique.
Figures 3.24 and,3.25 show, for the combined western 3.4.1 Accuracy of flood frequency tat¡o Or/õ
and eastern areas, respec
was fitted to the two types
the extension method arç
tern generalised curve id
marised in Table 3.7.
T¡ble 3.7 Summary of the characteristics of the generalised
curves.
al curve, it is
of statistical
sets of flood
peak data used to define the curye _ if different sets
of records of equal length had been available the curve
would be different; and
(b) tne spatial variation due to the curve being taken as an
of the flood frequencv relation-
ï"t#iltriiLt iJerage
Since in this study a regional curve is interpreted as the
o./o_
o,o/_o
Oro/O
O.o/õo,@/_o
O'æ/Q
O¡æ/O-
Oroo/O
u=
o= k:
General
Eq;ation:
4
Western N.Z.
1.18
1.42
1.67
2.O4
2.36
2.71
3.23
3.68
0.788
o.234
-o.1s6
O/O = -0.714+
1.502 exp (0.1 56yl
o/o
Eastern N.Z.
1.49
1.87
2.23
2.71
3.06
3.42
3.88
4.24
o.724
0.509
=O.724+
O.6O9y
var (a.b) = E(a),.var(b) + E(b),.var(a) 324
where E ( ) denotes the expected value and var ( ) the variance.
Errors of estimation in Q can be considered statistically
independent of errors of estimate in the regional curve ordinate
Q.¡/Q. Hence, applying the expansìon in Equation
Water & soil technical publication no. 20 (1982)

1^IESTEBN NEhI ZEÊLRND DRTR
Þ
o
Þ
o
t
Þ
ro
ooo
o
ê ê
l.0r t
ê
2.33
hESTEBN
1.50 2.25 3- 00
BEOUCED Y VRRIRTE
s
t0
ßEIURN PEN¡OD (YERNS)
NEI,,I ZERLÊND GENERRL I SED CURVE
o
t
o
to
ot
E
t
I - 50 2.25 3.00 3.75 {,50 5.25 6,00 l. ?¡
BEDUCED Y VRSIRTE
r.ort 2.t3 s l0 20 30 so 7s ir00 eoo 600 t000
NETURN PEñIOD
Water & soil technical publication (YEÊRS}
no. 20 (1982)
Flgute 3.24 Western New Zealand: the mass probability plot and the generalised curve.
45

46
EÊSTEFìN NEI,,I ZEFLÊND DÊTIì
o
Þ
o
o
di'
o
tct
a oê
.ü'
€
o
o
è
t.0tr
t .50 2.25 3.00 3. ?5 r¡.50
BEDUCEO Y VRßIRTE
2,33 S r0 ?0 30 S0 7s r00 200
BETUNN PERIOO fYEÊNS)
EÊSTERN NEI^I ZEÊLRND GENEI-IRL I SED CUßVE
o
,to -.rr . s0 2.2s 3.00 !,75 lr. s0 25 6.00 a.?S
NEOUCEO Y VFRIRTE
l.otr 2.!t s t0 20 !0 60 75 t00 200 s00 ¡000
BETUNN FENIOO ÍYEFñ5I
Water & soil technical publication no. 20 (1982)
Figure 3.25 Eastern New Zealand: the mass probability plot and the generalised curve.

3.?A, the variance of the flood peak estimate Q.¡ may be
given as (NERC 1975, p.184)
var(Qr) : var_(Q.Qr/Q) _
= E(Q)'.var(Qr/_Q)
+ E(Qr/Q)'?.var(Q)
325
The quantity var(Q ) on the right han_d side of Equation
3.25 depends on the manner in which Q is estimated (see
Chapter 4). In practice Q is substituted for E(Q ) and, similarly,
QrlQ for E(Q1/Q). This leaves only the quantity
var (Qr/Q) unaccounted for. It is the variance of the regional
curve ordinate Q.¡/Q at return period T and is the
type (b) variation mentioned previously.
The quantity var (Q1/Q ) was calculated as the variance
of the individual station flood frequency curves for
T=2.33,5, 10,20,30, 50 and 100 years. Given this variance,
the coefficient of variation (Cp) of individual station
curves about the regional curve is defined as
c¡ = (var (Qr/Q) )k/(Qr/Q) 326
and is a measure of the type (b) variation above'
Regression analyses of C¡ against the return period T,
and also fnT, were carried out and it was found that the relationships
between C¡ and /nT were approximately linear.
Regression equations of the form
Cp=(c+m./nT)/100 321
were therefore obtained, where c and m are constants for a
reglon.
The regression equations for the various regions are summarised
in Table 3.8. The square of the correlation coefficient
R was in the range of 0.946 to 0.992 in all cases but one,
indicating that generally the equations explained at least
9490 of the variation in C¡. The exception was the equation
for the Bay of Plenty region where the R'z value was only
0.380. This low R' value was presumably the result of the
regional curve having a different trend from some of the
frequency curves for the individual stations where there was
historical flood information. Further, the Bay of Plenty region
was the only one where the equation for CF was not
statistically significant at the l9o level.
While the statistical properties listed in Table 3'8 indicate
that the equations would generally be satisfactory for estimating
C¡ for a regional curve, some of the regions did not
contain sufficient stations to enable truly representative
equations to be determined. For instance, in three ofthe regiòns
less than l0 stations were used. Since the equations
were only a measure of the type (b) variation and were intended
to convey only an order of magnitude ofthe standard
error associated with an estimate of Q'¡/Q obtained
from a regional curve, it was decided to pool together the
individual station estimates of Q1/Q for different regions
into larger groups and to derive a new C¡ equation for each
group. These grou¡r equations could then be taken as the
estimating equatiorrs for C¡ for the regions they represented.
However, prior to the pooling of estimates, it was
necessary to dividr: the individual station estimates of
Qr/Q bv the corresponding regional curve ordinates.
Group C¡ values were then calculated for the pooled estimates
for the return period concerned.
Two groups of regions were considered for each of the
North and South Islands, with one group representing the
western and the other the eastern regions. Grouping the regions
in this mannen is supported by the overall trend in the
value for the slope m of the regional regression equations
(Table 3.8), with the value generally being greater on the
east of an island than on the west. This trend indicates that
the variance of the estimates of the regional ordinates
Q-¡/Q is greater on the east than on the west, and it also reflects
the greater variability in the flood peak data for the
eastern regions (see also section 4.9). Further justification
for this grouping of regions is given by the trend in the
characteristics of ttre regional curves (section 3.3.2).
The way in which the individual station estimates for the
regions were pooled together into groups is shown in Table
3.9. The estimates for the Bay of Plenty region were not
used in the derivation of the group equations. The C¡ equation
for this region was not meaningful in view of the low
R2 value and it thurs seemed inappropriate to use the data
for this region in deriving a useful equation for its group for
estimating C¡. The combined North Island West Coast and
South Island West Coast regions are the only regions in
their respective groups, and thus their regional C¡ eQuations
(Table 3.8) automatically became the corresponding
group equations.
Table 3.9 gives thre regression equations that were derived
for the groups andt it also lists the regions to which each
equation applies. The tabulated statistical properties indicate
that the equa,tions are statistically acceptable, with
each being significant at the l9o level. Table 3.9 gives the
100-year C¡ value as computed from each group equation.
The 1OO-year values range from 0.13 to 0.19 for the western
groups and from O.24to 0.25 for the eastern groups. They
compare very favourably with the value of 0.32 as given by
the corresponding Cp equation recommended by NERC
(1975, p.183) for use with all its regional curves.
Each group equation was derived from station estimates
for return periods only up to 100 years, even though most
regional curves extend to the 2(Ð-year return period. Normally
it is recommended that an equation should not be applied
outside the range of data from which it was derived.
However, in this case it was preferred to allow each equation
to be applied up to the 2D-year return period, rather
Table 3.8 The regional regression equations for estimated CF'
REGION
Coefficient
c
S ope
m
R2
s.E.
Est.
No. ol
Stat¡ons
NORTH ISTAND
1. Combined N.l. West Coast
2. Bay of Plenty
3. North lsland East Coast
4. Central Hawke's Bay
o.94
6.19
-2.21
o.25
3.93
o.91
6.O1
5.38
0.997
0.617
o.972
o.989
o.993
0.380
o.946
o.979
27.O* O.OO145
1.75 0.Oo518
9.32* 0.00645
14.9* 0.00361
65
12
12
8
SOUTH ISI-AND
5. South lsland West Coast
6. South lsland East Coast
7. South Canterbury
8. Otago-Southland
2.46
-o.37
4.53
-o.40
2.25
4.59
5.90
4.19
0.996
o.996
0.981
o.982
o.992
0.992
0.963
o.965
25.2* o.oo244
24.6* O.OO508
1 1 .4* 0.10410
11.7* O.OO974
21
14
9
t)
NOTE:
The regression is of the form C¡ = (c + m.fnT)/lOO
* ¡ndicates significance at the 196 level
S.E. Est. is the standard error of est¡mate of C¡
Water & soil technical publication no. 20 (1982)
47

Table 3.9 The grouping and the group equations for est¡mation CF.
GROUP
West N.l.
East N.l.
West S.l.
East S.l.
NOTES:
Regions whose
Data were
Regions Represented
Pooled Together by the Group
1
3,4 2. Bay of Plenty
3. North ls. East Coast
4. Central Hawke,s Bay
5 5. South ls. West Coast
6, 7, I 6. South ls. Easr Coast
7. South Canterbury
L Otago-Southland
Group
C¡ Equation,
C.=
1. Combined N.l. West Coast (O.94+3.93/nT)/1OO
(- 1.25 +5.74fnTl
/100
12.46 +2.25tnTll1OO
(2.61 +4.54/nT)/1OO
+ indicates significance at the 1 7o level
S.E. Est. is the standard error of estimate of C¡
No. of stations is the total number used in the derivation of the group equation.
S.E.
R2 t Est.
o.993 27.O* O.OO15
0.984 17.7' O.O0g2
0.992 25.2+ O.OO24
o.985 18.1* 0.0068
No. of C¡ value
Stations forT=1OO
65
20
2'l
29
o.1 I
o.25
o.1 3
o.24
than to obtain individual estimates of er/Q beyond a re_
turn period of 100 years, which would have involved a gross
extrapolation with several of the records.
C¡ equations for estimating standard errors associated
with the application of the generalised curves were also de_
rived, and in exactly the same manner and with the same
data as that used for the regional C¡ equations. Details of
the resulting CF equations are given in iable 3.10.
From a comparison of the coefficients of f nT in the
le 3.
can be seen that
for
rve produces CF
thin
given by the twô
that
area. This result
was not surprising, since a generalised curve for an area
represent
that area,
and so it
erages the
scatter in
plo-ts. Be_
cause of
d that the
Nevertheless, some of the curves and the associated regional
boundaries cannot be regarded as definitive because
of small data samples, a lack of samples, and a poor areal
distribution of the flow stations' catchmenti (section
3.4.3). In fact, the study exposed a number of areas where
efforts to acquire flood peak data should be concentrated
in the future.
In the South Island there were very few flow stations on
the coastal plains of the east coast. Here there are practical
difficulties in estabtishing flow stations because the alluvial
3.4.3 Definition of flood frequency
reg¡onal boundaries
As mentioned in section 3.3. I , use was made of available
3.4.2 Data limitations
most
ever
data
rves.
Island regions. A difference in the flood frequency trend
between the North Island stations in the west änd those in
the east was also evident.
Table 3.1O The C¡ equations derived for the generalised curves.
Area
Western NZ
Eastern NZ
cF
cF
Equation
S.E.
R R2 t est.
= (2.06+3.59fnT)/1OO 0.991 O.9Bt 16.3* 0.0060
= (1.79 +4.84hrV1OO 0.996 0.992 26.8* O.OO49
Water & soil technical publication no. 20 (1982)
No. of
stations
86
61
48

The regions that were chosen initiatly reflect the difference
in rainfall behaviour in New Zealand, and each region
can generally be distinguished by its own rainfall characteristics.
Where there are pronounced regional rainfall characteristics,
and where there are sound topographical reasons
for this, the boundary line between regions was easily decided
upon. For instance, in the South Island West Coast
region, where the rainfall is greatest and is dominated by
the orographic influence of the Southern Alps, the ridge
line of the Alps was the obvious dividing line between this
region and the other South Island regions. However, it is
probable that the effect of the West Coast rainfall extends
somewhat east of the ridge line, as indicated by the probability
plots for the Shotover and upper Wairau catchments.
The actual boundary line for the South Island West
Coast therefore includes these catchments and some eastern
headwater catchments in the Alps, e.g., the catchments of
the Wilkin, Makarora and Matukituki Rivers.
While the rainfall characteristics of different parts of
New Zealand helped to identify the regions, the actual definition
of the regional boundaries was not always as
straightforward as in the South Island West Coast example
the topographical features were not always as dominant
-
as the Southern Alps in influencing the rainfall. ln addition,
there was sometimes a poor areal distribution of flow
stations, so that often the definition of the regional boundaries
was rather subjective.
A striking outcome of the regionalisation work was the
small number of flood frequency regions. In earlier work
Toebes and Palmer (19ó9) divided the country into 90
hydrological regions according to climatological, geological
and topographical factors. However, in this study eight regions
were considered adequate to define the variation in
flood frequency behavioui in the country. This is an order
of magnitude less than the number used by Toebes and
Palmer, and suggests that climate is the dominant factor influencing
floods in New Zealand and that geology and topography
generally play relatively minor roles.
3.4.4 Homogene¡ty test
Some flood regionalisation studies have used the statistical
test described by Dalrymple (1960) to identify the stations
that form a hydrological homogeneous region. This
homogeneity test involves the graphical or analytical fitting
of a frequency distribution to each station's flood peak
data and the estimation of peak discharge values for the
2.33 and lO-year return periods, i.e., Qt ,, and Q,o respectively.
The ratio of Q,o/Q, ,¡ is then formed, which is an index
of the straightJine slope of the fitted frequency curve between
the two return periods. The test places confidence
limits on the ratio Q'o/Q, ¡¡ and stations with ratios lying
within the limits are taken as being part of the homogeneous
region.
Although the test Provides a quant
ing a region, it was not relied uPon a
insensitive when tested on South Is
served that the test was unable to detect even major differences
in individual frequency curves past the lO-year return
period. This deficiency ofthe test was also noted by Benson
(r962a\.
3.5 Flood frequencY discussion
3.5. I Regional d¡fferences
The most prominent characteristic of the regional curves
is that the curves for the western regions of an island have a
Water & soil technical publication no. 20 (1982)
regions receive more rainfall more regularly than their eastern
counterparts. Thus, the ratio of runoff to rainfall is
comparatively high for the western catchments and does
not vary markedly for the storms that produce the annual
floods. The mean annual flood is therefore fairly large and
there is little variability in the annual flood peak data (section
4.9). As a consequence, the difference between the
100-year and mean annual flood is not very great, e.g., in
the curves for the two western regions the 100-year flood
peak is less than 2.35 times the mean annual flood.
On the other hanLd, the catchments in the eastern regions
are usually drier and have a lower runoff to rainfall ratio.
The mean annual Ilood for an eastern catchment is therefore
less than that for a western one of the same size (section
4.5). There is eLlso a greater range in the runoff to rainfall
ratio fo¡ an eastern catchment and this is reflected in
the greater variability of the annual flood peak data for
such a catchment (section 4.9). The difference between the
100-year and the rnean annual flood is therefore significantly
greater than that for a western catchment, as is borne
out by eastern regional curves being steeper than the western
curves. It is worth noting that the wettest region (the
South Island West Coast region) has the flattest regional
curve and one of the driest regions (the South Canterbury
region) has the steepest curve.
While the slope of a regional curve is an indication of the
variability in the individual data samples for the region, the
curvature may be taken as an index of the skewness in the
samples. As indicated by NERC (1975, p.42,47), the EVI
distribution has a coefficient of skew of 1.14, and skew
values greater or ler;s than this figure correspond to the EV2
and EV3 distributions respectively. The majority of the regional
curves in this study are described by the straight-line
EVI distribution, implying that the average skewness in the
data samples for these regions was small. This in fact was
the case: for the regions with straight-line fits to the data
the average skew of a region's annual flood peak samples
was in the range 0.39 (S.I. West Coast) to 1.09 (Central
Hawke's Bay) and the EVI distribution was found to give a
good approximation to the regional data up to the 200-year
return period. In the Bay of Plenty, South Canterbury and
Otago-Southland regions the average skew of a region's
data samples was greater than 1.2. For the first two of these
regions, the EV2 dtistribution was found to give a good fit
to the regional dat¡1. Because of the smaller number of data
samples for the third region, however, less significance can
be attached to the average skew (1.23) of the region's data
samples, and the IlVl distribution approximated the data
satisfactorily up to the 100-year return period.
It is interesting to note that the two regions with EV2 regional
curves can both be regarded as dry areas; the South
Canterbury region because of its low rainfall, and the Bay
of Plenty region because of its absorbent pumice soils (see
also section 4.6.2) and its relatively low rainfall in comparison
with its regional neighbour to the west.
The pooling of the regional flood peak data to construct
the generalised curves produced mass probability plots
(Figures 3.24 and 3.25) that show very little scatter in the
data up to about the l0-year return period. Beyond this the
scatter is greater, but not excessively so, and is due in part
to some of the uncertainty associated with the historical
flood peaks. The averaging of the pooled data and the
application of the extension method (NERC 1975) clearly
defined the flood frequency trend for the fitting of each
generalised curve. rühile the curves require some refinement
using more and especially longer flood records, they
should still provide the designer with a reasonable guide as
to the magnitude of flood peaks past the 2(Ð-year return
period, the maximLum upper bound of the regional curves.
An assessment of the reliability of each curve can be made
from an inspectiorr of the scatter in the corresponding mass
probability plot eLnd by applying the appropriate North
Island group CF equation (section 3.4.1).
49

allowing curves rather than just straight lines to be fitted to
the regional data with confidence. In this New Zealand
curve and the eastern curve is the straight-line EVl. This is
d generalised curves
ynn (1978) for Creat
given in Figure 3.26.
curve and the corresponding regional ones, results from in_
clusion in the development of the generalised curve of some
of the extreme flood peaks which had been excluded from
the derivation of the corresponding regional curves. While
there is a valid argument for the inclusion of these extreme
e still been too
thereby weightperiods.
been described
New Zeatand curves bear a remarkabl|t','"tJJr:i*t;tÏ::
to their Great Britain counterparts.
Although the two countries have broadly similar cli_
mates, New Zealand has greater extremes of wet and dry.
That the New Zealand curves do not reflect this with túe
western and eastern curves be
-
tively, in relation to the corre
- is possibly due to the ave
ment of the curves, i.e., the i
treme wet or dry climates is largely nullified by the lumping
together of these areas with others which are noticeãblt
drier or wetter, respectively. The fact that the western New
was used to describe the generalised curve.
ntinuity between
Oing generalised
"
. ;;,f.tïi'l"i::;
expectation. This may be viewed as taking a weighted aver_
age of the estimates.
3.5.3 Vadation within a reg¡on
3.5.2 Compar¡son with rhe Br¡t¡sh lsles
;
f
these curves reveals some remarkable similarities with the
curves obtained in this New Zealand study.
First of all, the British Isles regional curves display the
same trend of an increase in the slope of the curves between
those for the western regions and those for the eastern re_
gions the curve for the western-most
- region, the whole of
Ireland, has the smallest slope, whereas the curve for the
eastern-most region, East Anglia, has the greatest,
Further, the range of the ordinates of the British Isles
and New Zealand curves is almost the same at high return
periods. For example, the South Island West Coast regional
curve, which has the smallest slope of all the New Zéaland
very dry in relation to
is likely to be steeper
catchment which is ve
tend to have a flatter
An extension of this argument leads to the concept of
sub-regions which, although geographically part of a làrger
surrounding region, display a e/Q frequency trend of thiir
is
E
b
50
3.5.4 Secular climatic variat¡on
-In th9 regionalisation procedure described by Dalrymple
(19@), it is recommended that all the flood records should
be brought to a common base length by correlating the re-
Water & soil technical publication no. 20 (1982)

o
SOUTH AFRICA
to
o
,s.E. BRtTAtN
.,,'
EASTERN N.Z.
WESTERN N.Z.
-N.W. BRITAIN
23
Reduced Voriote
567
2.33 5to2050
-ffi
roo 200 500 rooo
Return Period ! yeors
Figure 3.26 Comparison of the New Zealand generalised curves with those f rom the British lsles and South Af rica.
-
cords with the longest reliable one. The aim of this correlation
is to remove the effect of any climatic variation that
might exist amongst the records of differing length. However,
the correlations are often so poor that there appears
to be very little advantage in attempting this form of extension.
Further it is uncertain at the present time whether
there are significant climatic trends in annual flood peak
records (ICE 1975, pp.76-80). For example, Cunnane
(NERC 1975, pp.l25-32) performed a number of statistical
tests on 28 long records of annual flood peaks. The tests
suggested that the peaks were largely random, and therefore
contained no noticeable climatic trend. A similar con-
clusion was reaclned by Beard (1977) in an analysis of annual
flood peaks in 300 long records for stations in the
United States.
In this New Ze:aland study it was assumed that there was
no climatic trend in the annual flood peak records. This
same assumptiorn was made by NERC (1975), and in
Beard's (1977) flood frequency analysis work for the U.S.
Water Resources Council. The possibility of there being climatic
variations in the flood records is not ruled out, but
this is an area ol'hydrology that requires further research
before proper account can be taken of such variation in a
regional study like this.
Water & soil technical publication no. 20 (1982)
5l

3.5.5 Extension method
The NERC (1975) extension method proved very useful
in developing the Bay of Plenty regional curve and the generalised
curves. However, it was not considered necessary
to use the method for the development of every regional
curve. For instance, in a test on the South Island tr)Vest
Coast regional data, the extension method produced a
curve almost identical with that obtained by the usual
curve-fitting procedure (section 3.3.2). There was also uncertainty
in the method concerning the statistical dependence
between the original and the new set of average values.
In a sense it appeared that the same information on the
large Q/Q values was being used twice. This would weight
the curve-fitting process in favour of the historical flood
peaks, the estimat€s of which are generally less reliable than
those for the annual flood peaks. In addition, there is considerable
difficulty in grouping the stations of a region such
that neighbouring catchments are not represented in a
group. While this condition can normally be satisfied, there
are necessarily some catchments represented which are in
close proximity to one another, which raises doubts about
treating the flood peak data of a group as independent sample
items.
3.5.6 Catchment s¡ze
Catchments less than 20 km'? were omitted from the
study, except in the Northland-Auckland area, on the prior
belief that they would have steeper flood frequency curves
than the larger catchments (section 3.2.1). This was found
to be true at times, especially for the very small catchments
of the order of I km' in area. However, the initial curve for
the Northern North Island region (Figure 3.8) refutes the
general argument against the omission of small catchments.
The curve was based on the flood peak däta for catchments
ranging in area from 2.48 to 1606 km':(see Table 3.2), yet it
is not steep nor does the corresponding regional probability
plot show greater scatter than that for other western regions.
The curve is a typical western one and flatter than
any eastern regional curve.
While it was quite evident that the flood peak data for
some small catchments could not be tolerated in the derivation
of a regional curve, it does appear from the Northern
North Island example that small catchments could possibly
have been considered in the derivation of some of the
curves.
3.6 Summary
Eight flood frequency regions have been defined for New
Zealand, and an average Q/Q vs T curve derived for each.
It is suggested that these regional curves can be used to estimate
Qr/Q for rural catchments within the region concerned
for return periods up to 200 years. An exception is
the Otago-Southland curve; it is only tentative and should
not be extrapolated beyond the 100-year return period. For
return periods exceeding the recommended upper limit of
the regional curve, one of the two generalised curves developed
for the east and the west of New Zealand can aid
the estimation of Q1/Q. With all the curves it is important
that they are not applied to catchments whose areas are too
far outside the range of areas used in the derivation of the
curve concerned. An indication of the reliability of a Q1/Q
estimate taken from a curve is provided by standard error
equations, which give values somewhat less than a similar
equation determined by NERC (1975) for use with the British
Isles curves.
The most notable characteristic of the curves is that those
for the east have steeper slopes than those for the west, reflecting
the greater variability in the annual flood peak data
for the eastern catchments. The same characteristic is evident
in the British Isles regional curves. Also of note is that
the two New Zealand generalised curves resemble their
Great Britain counterparts (Stevens and Lynn 1978).
52
Water & soil technical publication no. 20 (1982)

4 Estimation of mean annual flood
4.1 lntroduction
This chapter covers estimation of the mean annual flood
1Q¡ tor sites with no flood record. A procedure is presented
which estimates Q as a function of catchment and climatic
characteristics. Where necessary, Q so estimated is designated
Q "s
distinguishing it from Q o5, calculated from
observed flood records.
The flood records used to derive the procedure were selected
as outlined below. This selection was based on the
length of record, the size and type of catchment, and the
quality of record. Selection of the characteristics and their
abstraction from maps and other published information are
detailed. It was found that improved estimates of Q were
obtained by forming regions. Delineation of these regions
and obvious boundary problems are discussed. Catchments
with records not fitting into regional patterns are identified
and reasons for some anomalies are suggested. Best fitting
equations are summarised with accompanyinig standard error
estimates.
4.2 Proposed method
The relation between Q and measurable catchment characteristics
was assumed to have the fo¡m of
Q: a X' b'X, b' 4t
where a, b,, b, ... are constants to be estimated and X', X,
... are characteristics of the catchment having an influence
on the mean annual flood.
After taking logarithms, log a, b,, b, ... were estimated
by standard multiple linear regression. There is good precedent
in the literature for this type of multiplicative function
(NERC 1975; Benson 1962b); thus other possible forms
were not investigated.
4.3 Records used
Catchments used in the study were selected from those
having an area within the range 0.22 to I 100 km'. The three
smallest catchments have areas 0.22, 0.52 and 2.18 km'.
Smaller catchments were excluded because flood discharges
from very small (often ephemeral) catchments result from
short duration rainfalls and are sensitive to infiltration and
vegetation effects (Campbell 1962). The upper bound was
imposed because estimates of mean rainfalls over large catchments
can be unrealistic. In any case, since most large
catchments in New Zealand are monitored, most ungauged
catchment estimation problems occur in relatively small
catchments.
Records for catchments with significant impoundments
or diversions were not used. This meant excluding a number
of lake outflow records. However, outflows from all
larger lakes are monitored for hydroelectric purposes and
flood estimates for them are best derived directly from
these records. Urban catchments, and others with areas of
limestone country, or permanent snowfields or glaciers,
were also excluded.
Four years of re_cord were considered the minimum necessary
to estimate Qou, md with the above constraints, data
for 63 South Island (Figure 4. I and Table 4.1) and 97 North
Island (Figure 4.2 atd Table 4.2) catchments were assembled
for the study. The distribution of these catchments
throughout the country was reasonable, except that there
were too few in the southern part of the South Island'
Tables 4.I and 4.2 contain the data used in this chapter.
These are the mean annual flood Qo6, , the coefficient of
variation Cu of annual maxima, the length of record, catchment
area, and other catchment and climatic characteristics.
Generally, flow data are complete to the 1976 or 1977
calendar year.
4.4 Collect¡on of character¡st¡cs
A number of indiLces can be used as characteristics X,, X,
... in Equation 4.1. However, if the relation to be developed
is to be useful as a design procedure, the cha¡acteristics
must be rea'dily obtainable from published information
such as maps, climate summaries, etc. The characteristics
can be subdivided into two groups; those which
cha¡acterise the phvsical catchment, and those representing
the climate over the catchment. The physical characteristics
included the size arnd shape of the catchment and the embedded
stream channel, the vegetation, and the hydraulic
properties of the soil. The NZMS I (l:63360) map series is
the most detailed map series giving a national coverage and
was used to providr: measurements of the area, mean elevation,
channel density, main channel length and slope, and
percent forest cover. Hydraulic properties of the soil (e.g.
permeability) are less easily defined; these depend on soil
type, surface slope, vegetation rooting characteristics and
underlying geology, and vary widely over most catchments.
Much of this latter information is now available nationwide
from the National Land Resource Inventory Iùy'orksheets
which are plotted at the same scale as the NZMS I map
series, but this was not available when the present study was
undertaken.
Climatic data available in Meteorological Service reports
and maps include rnean annual rainfall, rainfall intensity of
specified probability, distance of the catchment from important
meteorological barriers, and measures related to
the time and rate of snowmelt. Snowmelt is generally not an
important flood-producing mechanism in New Zealand and
in this study two rainfall parameters were used: mean annual
rainfall for the catchment, and the 2-year return
period 24-hour duration rainfall estimated for the catchment.
Thus the following characteristics were estimated for
each catchment:
Catchment area.
Water & soil technical publication no. 20 (1982)
(i)
(it) Main channel length.
(iii) Main charurel slope.
(iv) Mean catchment elevation.
(v) Stream frequency.
(vi) Percentagecatchmentforested.
(vii) Mean annual rainfall over catchment.
(viil) 2-year return period, 24-hour duration rainfall.
The first six of these are physical and vegetation characteristics
which were extracted from the NZMS I maps.
Although recent nraps in this series are photogrammetric
maps, earlier maps are based on survey records and plane
table sketch surveys. Others are provisional without contours,
so channel slope and mean elevation could not be defined
for every catchment. The considerable variation from
one map to anothcr in the definition of streams meant that
estimates of the sl:ream frequency, that is, the number of
stream junctions lper unit area, were unlikely to be consistent
from one area to another. It was felt important to
utilise all available information so stream frequency was included
but, in the event, it did not assist in explaining the
variation of Q between catchàents'
The procedures for estimating the physical characteristics
which were adapted from Benson (1962b, 1964) and Newsom
(1975), and acronyms by which these cha¡acteristics
will subsequently be known are given here.
(i)
Catchment area: (AREA) (km')
Catchment boundaries were drawn on maps and the
enclosed at'ea measured by planimeter. These areas
are normally available with recording station information.
53

Table 4.1 South lsland catchment characteristics.
1rì
11
2It
2(¡
27
28
21
30
51
32
51
Jlr
55
l5
37
38
lq
h0
41
lr2
ll'¡
qq
b5
46
lr7
q8
49
50
51
52
53
54
55
56
57
58
59
60
61
62
6l
o ^.-
STATIoN tm{il
5?tì16 tlÏ-.nni
5 7008 l¡37.00
57106 6S.20
5750! 83t.00
59001 77.nr\
6fìl 10 1161 .74
601tli 260.00
6fì1I6 59.f10
62!.0t 133.f'n
62104 -1.6.80
621rì5 187.fllì
64t01 524.n0
6460C 89.2fì
64610 1I.30
651n4 540.00
65q02 56.n0
66409 0,27
6660J 1.05
66604 1,42
67601 lt.?0
6Î001 35.00
68806 108.00
69506 260.00
696I lr 25 0 .00
61 618 I 20 .00
61621 72,7i
717î2 tJ.0n
7!LO3 11 2. 70
71106 91.60
71109 100,I0
71116 227 .nn
7lr2t 67.5tì
71f22 7,Jtt
lLlz? 16.10
711 29 2b . nn
711t5 6l .fio
7!702 148.0n
73501 37,80
7rr5l,h 55,2rì
TttSItE 22.F,rt
74t5i 2.87
7tt7Ol ,1-0.00
75259 22.20
7527 6 ll5 6. 0 n
7850-\ t0.00
73625 46.60
78801 5.09
80201 18.70
th701 5h9,00
86802 3725.00
906 0tt 2132.0î
90605 27 .iî
91101 1588.00
911102 lq.10
9!lr0h 692.00
91407 119tì.00
9!206 1680.00
91207 460.00
9t'2on 7rB.no
932u 974.00
91212 196.00
932t7 181.00
94502 1 251 .flo
cv
0.1n
0.85
0.79
0.tfj
o.7n
o.lrb
0,¡0
0 .10
0.55
0 .95
n.lr8
0.70
0.27
| ,17
ll.t!7
0.70
1.54
1.1i
I .01
0.fi8
0.5'r
0.71r
0.75
0¡98
r.l5
0.61
0.81
0.77
0.58
0.1 I
n.5lr
I .14
o.70
0.h7
0,11
n.75
1.nt
0.1 1
n,56
0.59
r) .96
0.30
o.26
0.lrl
0.1)0
0.81
n.78
o .2P,
0.!.6
0.10
o.2tl
0 .15
o.2t
o .27
0.r4
0.40
0.28
0.59
o .?.7
0.20
o.32
l-ength
Record
(yrs)
8
6
15
5
16
25
11
18
5
73
t2
10
3
10
It
5
t2
I2
6
16
I
40
lll
10
5
1l
(;
6
L2
7
6
q
11
10
6
72
10
10
L3
7
7
11
7
It
ll
7
9
6
9
1l
11
13
IJ
16
11
5
AREA MARAIN 1224 LENGTH 51O85
{km'¿) {mm) (mm} (kml (m/m)
5lEû0 287r !.10 16.50 0.0198
161.00 2100 Rl 25.10 0.(tr00
B1 .60 1140 81 20,50 0.0134
1164.00 1500 124 16.50 0. CI79
_l1,fta 7620 9t 6.50 0,n210
76b.00 14Lo 3t G1.so oi'riis
505.00 L6L0 69 4C.00 0.0118
192.00 24!0 69 29.40 0.0140
q9?.00 1570 76 68.90 0.0092
2n.00 7200 76 9.rlo 0.0600
440.00 L720 7l) st.tO 0.0097
464 .00 L23\ Lt2 49. q0 0.0109
7r,.60 4300 7ß L7.tt} 0.0290
41.60 030 74 10,50 0.0120
1070.00 2000 0t 76.10 o;00i2
tlz.2o 7\0 77 li,40 0.0270
o.22 L4C0 8l O.lO 0.20r¡0
?.13 1GO 63 2.50 0.1280
1,2t |to GJ 2.70 0.1ir0
5.20 l.rr00 !.04 Z.trO 0.1t¡00
16r; .0 0 1100 6 9 10 .7 0 O, (07 9
q?1.q0 L35o 6c 54.90 0.0140
t20.00 1010 80 t,6.BO o.oijO
456.00 1075 61 r¡6.40 0.0262
41 2 .0 0 777 61 tti .ZO 0 .010 6
2?.\9 800 52 7.eo UNDEF
78.70 ejo q1 2t: (o úi¡óEÊ
899.00 720 48 62.30 uilDEF
150.00 s70 q1 29.50 0.0070
23,7i lr30 3\ 9.10 0.0470
11.40 tz(J bi 10.10 0.0160
122.00 [00 J5 25.t0 0.0420
108C .00 7022 75 06.00 0.005 6
1!!.90 1010 rrr 2e.10 0.0020
109.00 10t0 51 17.10 0.01ió
36.80 10r!0 b6 17.!.0 0.0030
, u 1.90 lt t0 66 L7 .70 0,0070
155.00 6520 520 16,30 o:fì'riõ
842.00 6920 tO2 7rr,00 0.0168
152.00 731,0 ttl ,1.40 lt.0290
3.99 1500 18s 5.20 0.0560
99q.00 5700 226 65.90 0.0067
_lq.qq 27\3 104 8.90 0.0190
642.00 4010 81 66.s0 o.noõé
790.00 l¡1r70 8l 62.50 0.OOBO
99e.00 3580 81 69,50 0.0082
254.00 2520 81 15.60 o,ollo
980.00 2990 64 95.00 0.0091
E:7.SS i250 64 75.20 0.0120
-2!!.gg 1610 6b
1e8.00
2t.Eo ö:diii
t070 64 th.1o 0:ótÉ,,
694.00 \720 LS2 116-10 0.0170
FOREST
{%)
4t
4t
62
57
22
7
19
2
0
1
2
5
25
1
32
0
0
0
9
0
11
0
0
0
1
0
0
0
0
0
3
0
0
0
0
0
0
29
0
0
0
8
0
2
0
0
99
26
49
2f
78
56
16
76
58
76
77
7t
72
76
67
77
STMFCY ELEV
(km-'z) (m)
0.16 Ln'
0.48 1019
0.89 52tt
0 .71 587
0.80 594
0.87 785
0 .2\ 1 qll
0,21 t392
0.62 1510
0.02 11q0
0,r5 1200
0,72 500
0,27 rb20
0.41 5t5
0. b6 960
0.55 UNDEF
0 .0 9¡¡5
0.0 2E'1
0.0 r18
1 .60 t 0ll
0.78 647
0 .1¡r 100O
0,51 .820
o.ql 917
0 .25 5lr0
].10 UNDEF
1.80 UNDEF
O. 85 UNDEF
l.tt 827
L .72 1128
0.85 12b0
0.46 l0llr
0.11 840
o.25 970
o.22 lt85
0 .3t 1l¡90
1 . 1O UI,¡DE F
0. t5 288
1 ,71 83t
r.r1 913
2 .62 3lr 2
5. (l) L75
L.3t 1t68
0.28 tt88
0,08 50
1 .05 38'
0.0, 69
o.z\ 162
0.15 8b0
0,¡2 1050
0.56 1150
0.0 2\0
0 . 74 8l+t
1.08 L\2
0.17 7 20
0.21 710
0.t3 610
0 .26 860
tr zE 'TtÌ
0.25 971¡
0.50 679
0.2[ 1168
0.50 700
(ii)
(iii)
(iv)
Chsnnel length: (LENGTH) (km)
The main channel of the stream was defined and extended
to the catchment divide, and its length meas_
ured with an opisometer.
Channel slope: (51085) (m/m)
Two points were chosen at l0 per cent and g5 per
cent of the channel length from the outlet. Channel
slope was determined by dividing their difference in
elevation by % of the channel length.
Catchment mesn eleyrtion: (ELEV) (m)
A grid was overlaid on the map, the grid size being
selected such that at least 20 points lay within the
catchment boundary. The elevation of each point
within the area was noted and the mean of these
elevations was taken as the catchment mean elevation.
(v) Stream frequency: (STMFCY) (tns/km,)
The number ofjunctions for all stream channels de_
fined on the catchment map was counted and expressed
as the number per unit area.
(vi) Forest cover: (FOREST) (Vo)
The area of catchment defined as forest on the
NZMS I maps was measured and expressed as a percentage
of the total area.
54
(vii¡ Me¡n annual rainfall: (MARAIN) (mm)
Mean annual rainfall for the catchment was estimated
from records for rainfall stations within and
adjacent to it. Where catchments had no such rainfall
records, mean values were obtained by planimetry
from l:500 000 isohyetal maps of l94l-1.} annual
rainfall normals (NZ Met. Ser. (1977) ..Mean
annual rainfall maps (1941-70),' unpublished). In
mountainous areas having few raingauges and large
rainfall gradients, the isohyets are believed to indicate
only general trends and do not provide accurate
estimates of catchment rainfall, particularly in the
catchments draining the Main Divide of the
Southern Alps.
(vüi) Rainf¡ll intensity: (1224) (mm)
At the time of the study the most recent source of
published rainfall intensity data for New Zealand
was Robertson (1963). This provides frequency analyses
of rainfall intensity information available in
the early 1960's, using data for 46 recording rainfall
stations and 468 daily-read stations. As there were
relatively few records from recording gauges available
to provide short period rainfall data, the areal
extrapolation of this information to catchments
remote from gauges was considered unwise. It was
Water & soil technical publication no. 20 (1982)

Cobb.
5291ó '\
Stonley Bkr \
57011. \
Moluckor \ 7
57008 '. ¡.
rWo i¡oo
'P7so2
I
I
I
lnonoohuor \ \
93266 'r \'
liåî";--- )-l
lnonoohuo- \
932Õ7 -:-
er96iyt- )
Eîidt" tn--
Toromokou
9lrol --:
Butchers Ck :
90ó05 \
Hokitiko:
?9ó04 \:
-/
óó4O9 Hur Ck--
71.129 torksr - :
Fiï!Ë'" t'., 'r_ f
- Io-llie. '. \
7t135 \.
ffiåä'"n..
"...!
'r'
I t 59003
\ao,r,no
'
( \ óono'
twoi¡ou
\ óoìl¡
\ \wo¡rou
,- r óOlló
r \. rConwoy
\. ó4301-
\ \
'Achoron acha¡an
\ ó2103
I I \Sronton
i r \ ó4ólo
ì r i r'Áls9re ¡Ribblc
'-
ì !¡ ó2104
\ L-Clo.cnce
\ ó2105
-Weko Ck
t\- v¿ 6s902 ava
*, -- coshme¡e
- óóó03
- sHoon Hov
\ \- óóól 66601
\ s.r*y.^R'vi#Éi
Srh
lwo¡hooo¡
Rowollonburn /
80201 \
e ',
\ wo¡hooo i
78sOc
- gå3g5'
Fþure 4,1 Location of the South lsland catchments.
Water & soil technical publication no. 20 (1982)
55

I
2
t
l¡
5
5
7
I
9
l0
t1
,12
I5
1{
l5
l6 t7
18
19
20
2t
22
23
2lt
25
26
27
28
29
t0
t1 t2
t,
5\
t5
56
,7
t8
39
¡0
¡1 tt2
Irt
4h
Ir5
It5
47
|l8
It9
50
51
52
51
5lr
55
56
s7
58
59
60
61
62
63
6lr
65
66
57
68
69
70
7t
72
73
74
75
76
77
78
79
80
8t
82
It
84
fì5
86
87
B8
89
90
91
92
g3
fth
.,5
96
97
TaHe 4.2 NoÉh lsland catchment characteristics.
_
L€ngrth
065¡ ^ Roco¡d AREA MARATN 1224 LENGTH s1085
STATION lm¡s-r) (,v lyrs| (kmrl lfnm) (mm) (km) (m/ml
t506 57.80 0.29 10 11.10 2250 105
5819
7.00 0.0260
107.00
11901
0.¡4 10 229.00 1510
83.90 0, l+lr
109 ¡10.10 0.0014
I 12.5 0 19 q0
5809
l2t+ 4.60 0.0091r
63.30 0.67 10 16.20 l7 00
8501
102 7.L0 0.0510
tL.20 0.55 15 t2.70 17 90
s10t
74 8.50 0.0150
q2 .10 0.4s t7 455.00 15 00
9108
69 75.00 0.0010
tl0.00 0.64 L7 528.00 L230
9201¡
71 43.50 0.0020
[92.00 0.28
92QB
t3 t08.00 ztr0 119 ,5 . lr0 0 .0010
t 5. t¡0 1.05 7 7.90 t9 20
9501 519.50 0. r+2
llf 4.00 0.17 20
18 l22.OO 5090
15901
8q 21.80 0.0177
5.06 1.20 6 2.95 15r 0
Ur6l0 20.t0 0.t8
10tl t.80 0,01+50
I 57.00 150 0
Ltt627
86 16.90 0.0100
¡rt.40 o.37 10 69.90 2L20 104 2\.20 0.0170
10528 147.00 0.52 I 179.00 22tt0 108
151r10
31.50 0.01q0
120 .50 O.75
15511
25 53t¡.00 L730 84
t87.00 0.60
55.t0 0.010rr
25 q¡0.00 17 90
l55rl¡
12ì+ l0.2o 0.0130
2.11 0.65 10 2.59 l5 t0
15556
95 2.66 0.0515
218.10 0.46
15901
8 207.00 20¡0
819.00 0,65
lztt 28,70 0.02b3
19t09
19 640.00 217 î 91 50.70 0.0088
14rr.00 0.29 t2 lst.30 1¡0 0
19711
79 21r.10 0.0216
t70 .00 0,65
21601
11 175.t0 llr00 8l 27.tO 0.0158
59.60 0.52
218 05
l0 20 .60 142 I lztt 7.00 0.02!8
45 9.00 o
22802
.52 13 997 .00 22tO
216.00 o.77
99 72 .50 0 .0060
23002
13 25t¡.00 15 01r
501.00 0.64
99 31.60 0.0150
2too5
10 826.00 154 0 92 67.10 0.0070
1,51 0.40
2tl0tt
10 0.52 2605 86 0.50 0.01180
209.00 0.32
2tL06
t3 570.00 1450 9lr 62.10 0.0080
66,30 0.48
21209
t0 259.00 160n 70 t4.60 0,0110
10.50 0.90
232LO
t2 24.10 955
48.70 0.57
66 7.60 0.0086
10 54.q0 t277
2920t
t02 t'.30 0.0040
{29.00 o.27
29224
22 6t7.00 16 60 66 5q.60 0.0080
532.00 0. 28
29211
22 185 .00 \t+7o
156.00
rrl
99
292\2
I
58.00 0.0210
t|t .O0
89.00 0.40 '9
1110 7tt 68.10 0.00t1
58.80 Ir00ll
2921t4
6l+
27.60 0.111
16:70 0.0410
I 56.t0 1090
29250
76
31.70 0.87
15.50 0.0064
7 15.50 18 40
29808
107 5.70 UNoEF
254.00 0 .t2 9 88 .80 2410
29818
99 14.60 0.02110
546.00 0.28
t0516
6 427.00 2700
7.86 0.112 B
79 38.1¡ 0.0050
0.t5 10t n
,180t
69
1027.00 0.15
7.60 0.0102
l8 50r.00 2670
t2so3 539.00 0 . ¡ll
102 ¡9.90 0.0116
32526
22 71t.00 15 r0
719.00 0. l¡0
78 67 . t0 0. 0050
24 266.00 2tt7
12529 262.00 0 . ltg
î 100 65 .20 0. 0060
24 7t lr .00 15 70 6h 5t . l0 0.0010
t25rt b3r.00 0.37 2\ [52.00 1780 8J 55.t0 0.00110
t2565 18¡.00 0.26 10 570.00 12 60 60 92.00 0.0100
32576 5t7.00 0.56 8 bt1.00 15 70 79 56. ¡0 0.0160
12708 522.60 0.t2 10 58t.00 2t 00 76 76.00 0.006t
52721 21.70 0.¡t 7 25.60 t1 l0 52 9.5 0 0.01t9
32712 106. 00 0,35 17 285.00 2260 5l ,t.00 0.0140
32711 182.00 0.]5 5 650.00 178 0 55 70.00 0.0110
,273\ 5 .11 0.16 15.00 I 701 51 8.20 0.0550
t2735 t2.\0 0.67 8 62. [0 920 55 20.90 0.0100
J27t9 18.70 0. b8 t2 47 .70 I 100 52 1t.50 0.0087
,5707 96.5 0 0,19 l0 1192.00 1650 58 51. .00 0.OL72
3t111 240.00 0.35 lt 5t9.00 157 0 69 59.70 0.0168
t1114 lr,18 0.18 9 6t.50 1101 55 15.20 0.0110
StlLs 19.70 0.17
ltll7 t3.20 1568 66 8. 20 0.0b70
25.10
ttt07
0.51 I 21.04 2160
h0.70 0.¡5
7t 20.90 0.0400
11 81.5u 2¡¡00 toz 7.70 0.0901
3tt09 t21.00 0 .26 15 132.00 2220 7t t8.00 0.0326
35tlL 265.00 0.11 15 207.00 219 0 89 60.00 0.0058
35112 350.00 0.69 6 256.00 19 40 7\ 26.90 0.0159
t33t3 268 .00 0 .5 0 15 668 .00 180 0 19 82 .40 0.0018
5t316 259.00 0.24 14 1075.00 7770 74 72.00 0.0049
31320 0.28 L7 181¡.00 1220 t02 2a.L0 0.0519
tt324 '82.00 41.60 o.52 8 tl .00 2592 102 16.00 0.0417
55538 512.00 0.15 I 971.00 2160 8lr 66.!0 0.0172
31t47 125.00 0.20 5 207.00 18t 0 89 5tr.l0 0.0025
50.90 0 .46 10 28 .00 2rt0 90 tq .60 0.0650
'tttt7 ,6001 t8.90 0 .60 f 29.50 23L0 79 25.60 0.01110
19501 572.00 0.29 8 725.00 2280 97 l[0.00 0.0005
10504 175.00 0.12 t2 80.00 ,582 104 28.60 0.0298
39508 (t7.2O 0.51 4 11.t0 1582 104 17.50 0.0580
rl 07 0l 5 .24 0.2t 7 15.60 207 0 74 5.00 0.0280
41601 7.\3 o.52
t+3ttt5
5 9.10 15 90 611 11.60 0.0520
45 .20 î-25 t1 157.00 195 0 81 10.40 0.0502
\1472 21.1 0 0. 61 16 228.00 t270 76 21.60 0.0050
10¡3419 27.60 o.52 73 446.00 1500 66 q1.80 0.0120
1043\27 58.90 0.1 7 14 t7t.oo 1880 72 t7 .3ît 0, 0102
10¡t428 44.90 0.t4 72 210.00 1q00 90 21r.50 0.0100
104tlt5lr 5.68 0.70 I 22.00 1¡t 0 76 11.50 0.0250
1043459 î.82 20 772.00 2270 88 62,80 0.0120
104t461 '65.01 241.01r 0.29 t7. 174.00 2980 89 11.80 0.0187
104tt66 [7.50 0.25 25 88.00 5580 76 b.90 0.1010
11113408 0.01 0.23 7 0.17 16 60 80 0.51 0.1500
Llttt\zz 5 . tio 0.68 6 5.11 2000 66 lù.50 0.0820
7145t+28 4,10 0. 44 B 17 .1¡0 llr 60 66 5.70 0.00llr
\3602 2r.50 1.32 9 17.60 lt60 75 5.70 0.0092
Ir3805 t9.90 0.66 I 52.60 1r4 0 69 18.50 0.0050
45102 t2.70 0.lr8 10 8.00 15 70 109 5.70 0.0t20
¡!6611 153 .00 0 .32 8 116 .00 16 20 117 22.70 0. 0190
46618 4l+7.00 0.46 17 2[6.00 195 0 ll7 26.80 0.0190
Ir6625 221.90 0.28 I 189.00 l5t 0 101 2t .20 0 .0040
\6612 189. lr0 0.52 t7 162.00 lB20 1tl7 20.90 0.0070
46660 9.72 0.t9 L2 2. b8 1540 t00 2.70 0.0210
45662 2.t1 0.r5 r0 0.t9 11r 90 117 0.60 0. 1000
tt7527 41.90 0.98 t2 10.60 I 800 llb 6 .00 0.0102
FOREST STMFCY
(%l (km{}
0 0.90
29 0. 45
¡8 1. E4
6¡ 1.70
100 5. l0
5 0.r1
0 0.50
tt5 2.10
t00 1.t9
82 2.t0
0 2.00
b5 I .00
55 1.50
57 0. 92
95 UNDÊF
89 UNDEF
0 t.50
100 l¡.70
79 UNDEF
O UNDEF
2 1.91r
o 2.13
50 UNOEF
12 UTIDEF
5 0.90
lOO UNDEF
[¡ 0.E0
Irl 0.80
5 UNDEF
o 2.\0
14 0.16
78 0.62
t 1.00
65 0, 49
0 1,00
l0 7.50
q5 1.50
55 L.rl
0 2.10
90 0.58
5 U¡IDEF
51 0. 66
2 UNDEF
t2 0.10
7 0 .116
22 0. lt7
l8 0.59
2 0i98
7 L.1L
5 1,t5
tf 5.50
0 0.69
I 1.15
t5 0.81
2t t.'l
0 0.6t
E7 5 .50
59 0.76
L2 0.96
56 L.77
85 0.96'
51 1.70
28 r.61
27 0.79
E 1.62
0 t.l¡8
ql L.27
58 0.71
0 1 .1r2
tt 0.q6
59 1 .50
2t 1.19
51 0¡62
16 1.10
0 0.55
55 0.65
5 I UNDEF
57 UNDEF
¡t 0,t8
t9 1.10
16 2.45
3L UNNEF
50 2.05
! 2.65
0 2.70
7 0.t2
0.52
0 1.20
6 1.50
57 r.00
llr 1.5t
ll 0.92
16 0 .80
[0 1.50
0,0
0 0.0
8 0. lr7
ELEV
(m)
2.50
tL2
180
16t
zilt
80
86
275
510
3ro
110
t99
lll6
,72
UNDE F
48lt
1t0
660
6q0
450
,20
l¡ ¡r
UNDEF
UNDEF
t92
10 10
1121
965
220
200
,0tr
726
265
672
280
UNDE F
6tr0
t+7\
ztt0
55'
8trI
Ir 66
UNDEF
29r
1.95
568
10 ¡rf
285
11 70
992
119 0
180
2tl
959
680
825
5
970
869
831
392
492
581
474
1108
861
726
t22
111 0
510
286
427
778
280
200
487
4 5l¡
160
527
4lrl
l+60
970
L202
900
610
[00 l0
50
ft
270
t10
t52
155
105
80
100
2t6
Water & soil technical publication no. 20 (1982)
56

Ooohi 17527'
Mongåkohio 46618'-
Koihu 16611" )
Puketuruo 4óóóOl
& Pukewoengo 4óóó2
(z'
,Woiwhiu
a
45 702
,Kouoerongo 93Oì
a 7/ ¡woit- gtol
Pìoko 9l08-
Ohote 1143428- - -
Pokoiwhenuo lO43419- -
\ Te Tohi 1143427-. -
Oteke 4ìó0'l1 \-
& Purukohukohu 'l143408
-Woimono l55l I
,Woimono ì553ó
/'
/ / Woioeko 15901
Popokuro 43803'-
Woiroo 85Ol- -
Woitongi 13602'-
- - -Woiotopu 43172
-whirinok¡ l54lo
--T
- - -Woingoromiq ì97I
- - -Whorekogoe l97O
,1',/
lO43¿59
rL
Y- - - -Tongoriro
:--
- .- --Tohekenui 2lóOl
- --Wongonui
-=ln --_-t
333¡7
- - -Mongolepopo 33324
- - Whokopopo 33320
It-L-
\t-
Mokotuku 33.l17 /
Woipopo 4343* -
Mongokowhoi 4O7O3- -
Tohunootoro 1013128- -
Mongokino 1C,13427-- -
Ongorræ3331ó - -
Mongoroo3334l---
Ohuro 333ì3- - -
Tongorokou 333 I l- -
Woitoro 39501 --;
Mongonui 39504--
Mongonui 39508-- -
Punehu3óOOl - - -
Wongonui 33338- -.
ñeørute 3g312/
Mongonui-o-te-oo 33309/ -.
,'
Mångowhero 33lll/ ./
üu-h""ã*h, 33107/ - -\,
MoungorouPi 32723¿,/t
Tuloenur 32739' /
Rongilowo 32735/
Mongohoo 32526- -
Mcngoloinoko 32531-'
ì,fhonqoehu 29211- -
Oroki 3ì803- -
Monooloroo 33ì15 /
-( j-îftx,t-t-\-
--
--O,rouo 325ó3
-Ti¡oumco 32529
Aliwhokolu 29242
ì,--loueru2923l
\- --Woiohine29221
/ -: -\Hutt 29808
-:- --Hurt 29818
-- - Ruohokopotuno 2'?250
'rv\iil ck 3o5tó
---
Rro-oho-ngo2.92Ol
Êigutø 4.2 Location of the North lsland catchments'
Water & soil technical publication no. 20 (1982)
51

decided instead to use estimates of the 24-hour dura_
tion 2-year return period rainfall derived from the
more extensive net$,ork of daily_read gauges, since
these could be extrapolated to remotè catchments
with greater confidence.
The use,of a 2-year recurrence interval seemed ap_
propriate because the mean annual flood has a rècurrence
interval only slightly greater than 2 years,
2.33 years if the annual ma,rimã conform to the extreme
value Type I (Gumbel) distribution. Estimates
of this parameter (without the application of an
areal reduction factor) were made from Robertson's
data for each catchment using rainfall stations with_
in, or near to, the catchment. These estimates were
not adjusted for effects of altitude.
These eight characteristics were estimated for each catchment
(Table 4.1 and 4.2 for the SI and NI respectively). For
those catchments not contoured, channel slópe and mean
elevation were undefined; there were 5 such bouth Island
catchments and 7 North Island catchments.
4.5 Analys¡s of South lsland data
4.5.1 Preliminary examinat¡on of data
table shows that the highest correlations of Q are with
AREA and LENGTH, but that signifìcant correlations also
occur with all other characteristics except STMFCy. Further
strong correlations occur between AREA and
LENGTH, between MARAIN andl2}4andalso MARAIN
and FOREST. These are all physically plausible. Significant
negative correlations occur between Sl0B5 and AREA and
not well determined.
The results of applying a, stepwise multiple regression
program to the data are summarised in Table 4.4. The best
fit equation is that involving the three variables AREA,
I2A and FOREST and is
Q = 4.40 x l0{ AREAÙ.¿'12241.27 (l +FOREST/lcf|/)t 6'
.....4.3
The coefficient of determination indicates that glgo of
of errors of estimate is given in section 4.10.
quently. For the present the data are considered as one.
with AREA (Figure 4.3),
rs of magnitude for Q for
approximate equation for
south of the island, and strongly positive residuals on the
Q = I.9SAREAo eo 42
where Q is in_m3ls. The linear correlation coefficient (R)
between loe (Q) and log (AREA) is 0.85, and the stand;rá
error-of_estimate of logarithms of Q is 0.45. Although this
correlation is highly significant, the standard errorls too
large for Equation 4.2 to be of much value, an obvious con_
clusion when the scatter for Q for any given AREA is con_
sidered (Figure 4.3). Equation 4.2 demonstrates two im-
this systematic residual variation may be due to variation in
the precipitation regime across the island not fully represented
by the estimates of 1221.
4.5.2 Development of tdal rcgionalest¡mators
into four regions is
of the high rainfall
the Southern Alps is
des the Nelson area
with the \Vest Coast. The division of the East Coast is more
tenuous, but is supported by the consistent underestimation
of Q for the small catchments along the coast (Figure 4.4),
and by the knowledge that some of the morè intenie
from cyclonic
inland. Specia
third inland
part comprises
T¡He 4.3 Correlation matrix for logs of South lsland characteristics.
MARAIN STMFCY s1 085. ELEV*
o
AREA
MARAIN
1224
LENGTH
FOREST
STMFCY
s1085.
ELEV'
l.OOO
.846
.612
.448
.799
.464
-.078
-.473
.383
1.OO0
.2e3
.045
.978
.163
,010
-.673
.460
l.OOO
.753
.228
.647
-.390
-.o51
.ioz
l.OOO
.o23
.424
-.314
.181
.o98
l.OOO
.155
.oo7
-.733
.424
l.OOO
-.259
-.134
-.092
l.OOO
-,049
-.o47
l.OOO
.10,4
1.OO0
I lncomplete Sample
58
Water & soil technical publication no. 20 (1982)

I ]n
e
d qgoinst CATCHMENT AREA for South Istond x
64
x+O
¡XOs
Xt
x
o
74314 Toieri
1é
x V,/est CoqsT
+ Eqst Coost
O Intond Morlborough/
Conterbury
O Mqckenzie, Inlqnd Ofogo,
Southlond
10
Iotch me n I
100
A¡e u (kmz)
1000 10000
Fþure 4.3 O vs AREA, South lsland catchments.
the inland hill country of Marlborough and Canterbury.
The southern part includes the Waitaki River basin, inland
Otago and most of Southland. This division is made on the
basis that with the exception of coastal Southland, the
southern part is a low rainfall area for which Q rvas overestimated
by the equation.
The regional division is evident in Figure 4.3. When the
catchments were identified according to the region including
them, it was found that data for West and East Coast
regions tend to lie in an upper band. Those for Inland Ma¡lborough/Canterbury
tend to lie in a central band, whereas
those for Inland Otago and Southland tend to lie in a lower
band.
The data were grouped according to these regions and regional
stepwise regressions were calculated (Table 4.5). In
all cases AREA is the most important variable, although in
all regions additional variation in log Q is explained by
other variables. In the West Coast, and Inland Otago and
Southland, rainfall intensity (I2Z)'signifïcantly improves
the fit of the estimating equations.
For the East Coast, MARAIN is the second most important
variable. The reason this is more important than I2Z is
therefore preferred.
Water & soil technical publication no. 20 (1982)
not obvious. It naay be that, because the East Coast catchments
are relatively small (the largest, Station 64301 is
464 km'z), the 2-hour storm intensity may be more important
than the Z4-hour figure used. However, such information
was not generally available. The appropriateness of
annual rainfall for estimating a flood parameter is open to
question, but it is supported by Figure 4.5. This figure
shows that, with the exception of Station 65Ð2, there appearsto
be a linear relationship between log MARAIN and
the residual of log Q, after the effect of AREA is removed.
This is the justification for including MARAIN in the estimating
equation.
For Inland Marlborough/Canterbury FOREST appears
as significant in the best-fit equation. However, this is a little
deceptive since only 4 of the 15 of the catchments in this
region are more than l09o forested and the ma¡

\Í
l{
I
t,
ìj(
Fþurc 4.4 Distribution of residuals from Equation 4,3.
Water & soil technical publication no. 20 (1982)
60

3.1
z
Í ¡.0
=
t:'
o
2-9
2-8
2.7 --4 .2
'l+
.ó
(roc õ-.sz LoG AREA)
Figure 4.5 Plot of log MARAIN vs (bg õ -.92 log AREA) for East Coast Region.
Table 4.4 Stepwise regressions for all South lsland data,
No, Var. Name
Coef
br
se
of coef
R2
se
€8t
Const
log a
Muhiplier
a
1 AREA
2 AREA
1224
3 ABEA
1224
FOREST
4 AREA
1224
FOREST
STMFCY
5 AREA
1224
FOREST
STMFCY
MARAIN
6 AREA
1224
FOREST
STMrcY
MARAIN
LENGTH
0.90
0.88
1.58
o.85
1.27
1.65
o.85
1.34
1.75
o.44
o.82
1.O4
1.34
o.54
o.39
o.95
o.99
1.35
0.53
0.41
-o.25
o.073
o.046
o,169
0.041
o.162
o.364
0.040
0.163
0.360
o.229
o.o42
o.222
o.412
o.230
o.202
o.202
o.236
o.414
o.232
o.204
o.373
12.4',
19,8*
9.3*
20.6*
7,8*
4.5"
21 .O*
8,2*
4.91
1.9
19.6*
4.7'
3.2*
2.4*
1.9 -
4.7'
4.2*
3.3*
2.3'
2.O'
-o.7
o.846
o.940
0.954
0.956
o.959
o.716
0.884
0.910
o.914
o.920
o.450
o.292
0.256
o.252
o.249
o.0333
- 2.866
-2.351
-2.571
-3.195
1.O8
1 .36 x 1O-s
4.46 x 1O-3
2.69 x 1O-2
6.38 x 1O<
o.958 0.918 o.262 -3.071 8.49 x 1O{
' Significam at 5% level.
Note: 1 The fitted relation is õ = a Xr h Xz b ...
2 The multiple correlation coefficient (R) and standard error of ostimato quoted 8re for tho logarithmic form
Water & soil technical publication no. 20 (1982)
logO = loga + br logXr + bzlogX¡ * .,,

62
Fþurc 4,6 Logarithmic rcsidual errors for trial South lslend regional equat¡ons.
Water & soil technical publication no. 20 (1982)

4.5.3 Examlnstion of residuals
The geographic distribution of the logarithmic errors of
the regional equations is shown in Figure 4.6. Except for
some possible clustering of positive residuals at the southern
end of the island, the errors appear to be randomly distributed.
Before the regional equations were finalised, the more
extreme errors were examined to see whether they could be
attributed to known causes. Errors greater than t0.25 a¡e
shown in Figure 4.6 for Stations 57008 (Motueka at Gorge),
64ó06 (Waiau at Malings Pass), 65902 (Weka Creek at Antills
Bridge), 68806 (Ashburton South at Mt Somers'),7ll02
(Otekaieke at Stock Bridge), 71122 (Maryburn at Mt
McDonald), 74314 (Taieri at Patearoa-Faerau Bridge),
78625 (Otapiri at McBrides Bridge), 9ll0l (Taramakau at
Gorge), atd9l4O2 (Sawyers Creek at High Street Bridge).
The following reasons are advanced as possible explanations
for some of these and other lesser outliers.
(Ð Cstchment in wrong region
For Station 64ó06 (V/aiau at Malings Pass) the error is
0.32. This small catchment (74.6 km') is adjacent to
the Main Divide and subject to the same heavy rainfalls
that cause many rWest Coast rivers to reach flood
levels. The West Coast region'should be extended
slightly to the east of the Main Divide to include this
catchment. Two other catchments (60114 and 60116)
lie near, but not generally as close to the Main Divide
and do not on the basis of their residual errors justify
inclusion in the West Coast region. This adjustment of
regions is supported by a rather abrupt cut-off of
north-westerly rainfall which seems to occur a short
distance to the east of the Main Divide. Also, Figure
4.3 suggests that Station 64606 fits better with the West
Coast catchments than with the inland catchments of
the Inland Marlborough/Canterbury region.
(it) Unreli¡ble e¡tlm¡te of Q from excessively short record
The error for Station 65902 (Weka Creek at Antills
Bridee) at 0,6 is the higlrest for all 63 stations. As an
error of about 0.33 would occur if the bounda¡y between
the East Coast and the Inland regions was
shifted slichtlv to include the catchment in the Inland
region, it-is óoncluded that Qo6, for this catchs€nt
ba--sed on only fóùr'years of recdiã is an unreiiable estìmate
and the station is not used in the subsequent analysis.
(lil) Catchments wlth large pondlng effects
The frrtted equations seriously ov€r-estimate Q for stations
68806 (Ashburton South at Mt Somers) and Station
71122 (Maryburn at Mt McDonald). Part of the
Ashburton South catchment and all the Maryburn
Region
1 West Coast, Nelson 1
Number Variable
Variables Name
2
faHe 4.5 Stepwise regressions for South lsland regions.
AREA
AREA
1224
Coef
br
se
of coef
0.87 0.103 8.5*
o.91 0.063 14.3*
o.90 0.165 5.4*
2 East Coast 1 AREA 0.92 0j42 6.5*
2 AREA o.91 0.081 11.2*
MARAIN 2.58 0.559 4.6'
AREA 0.96 0.108 8.9t
1224 1.62 0.557 2.9*
AREA 0.93 0.083 1 1.2*
1224 o.58 0.566 1.O
MARAIN 2.O7 0.14A 2.8*
3 lnland Marlborough/
Canterbury
4 Mackenzie, lnland
Otago, Southland
+ Designated beet fit equation
* Significant at 5% level.
Notes: 1
1
2
AREA
AREA
FOREST
AREA
FOREST
1224
AREA
1224
AREA
MARAIN
o.85 0.049 17.5*
0.83 0.042 19.9'
2.58 1.OO2 2.6'.
o.82 0.044 18.4*
2.58 1.032 2.5'.
-o.23 0.402 0.6
o.84 0.052 16.2*
-o.22 0.4A2 0.5
o.85
0.34
o.o47 18.z',
0.238 1,4
o.899
0.964
R2
se
est
Const Muhiplier
loga
a
o.81 0.2A7 0.560 3.60
O.93 0.181 -'l .381 4.16x1O-'z+
0.899 0.81 0.359 0.1 1 1 '.|.29
0.968 O.94 0.216 -7.600 2.51 x 10{ +
0.946 O.9O 0.235 -2'891
1 .29 x 1O-3
0.971 0.94 0.177 -7.149 7'1O x 1O{
0.979 0.96 0.175 0.0363 1.O9
0.986 0.97 0.152 0.O212 1.O5
0.987 0.97 0.129 0.455 2.45
0.980 0.96 0.162 0.454 2'84
0.982 0.96 O,1 51 - 1 .O3 9'33 x 1O-2
AREA 1.O2 0.131 7.8' o.89s 0.80 0.257 -0.706 1.97 x 1O{
1
2 AREA o.91 0.098 9.3* 0.947 O.9O O.1A7 -2.A97 1.27 x1O4 +
1224 1.40 0.367 3.8*
AREA 1.38 0.249 5.6* 0.957 0.92 O.180 -2'122 7.55x1O-3
t224 1.13 0,357 3.2'
LENGTH -o.93 0.460 -2.O
The form of fitted relation is O = a ¡¡'¡b' (Xzlb' "'
2 The multiple cor¡elation coefficient and standa¡d error quoted are fo¡ the lcgarithmic form
log O = log a + br log Xr + br log Xz '..
3 FOREST computed as (1 +FOREST/IOOl
Water & soil technical publication no. 20 (1982)
63

Table 4.6 Final equations for South lsland regions.
Region
West Coast. Nelson
East Coast
lnland Marlb, Canty
McK, lnland Otago, Sthld
No.
Stns
19
11
13
15
õ
õ
õ
õ
B€st Fh Equations R2
Se
est
= 0,0233 AREAo...l224o.e¡
= 1,1 1 x lo-e AREAo ¡e MARA|N3.o
= 0.964 AREAo.¡o
=o.oo1 90 AREAo.el 12241,3
o.971
o.989
0.992
o.963
0.94
o.98
0.98
o.93
Factorial
se €8t
0.1 48 1 .41
0.117 1.30
0.1 09 1 .28
o.1 46 1 .40
catchm€nt drain former glacial moraines on s,hich the
surface drainage network is ill-defined. Considerable
surface storage occurs in swamps and, in the case of
the South Ashburton, the drainage divide with Lake
Heron is ill-defined. Therefore, flood-flow levels are
expected to be substantially reduced and it is uûeal_
istic to use data from these catchments to estimate
flows for other catchments where similar ponding does
not occur. On this basis the data are omitted from the
final analysis.
The central area of the Taieri catchment (Station
74314) is a flat plain through which the river channel
follows a meandering course. The recording station is
situated downstream of a narrow gorge in which flood
waters back up and inundate large areas of the plain.
This ponding occurs to a much greater extent thãn on
most other catchments. The resulting reduction in
peak discharge is reason for rejecting data from this
catchment in the final analysis. Note that this catch_
ment is an outlier in the Q against AREA plot in Fig_
ure 4.3
(iv) Station wlth unreliable rating
Because flow records for Station 9ll0l (Taramakau at
Gorge) were derived using a theoretical rating the re_
cord qualìty was expected to be only fair andihe esti_
mate of Qo6, subject to more error than most values
for most other stations. As the value used appears to
result in a large error, the station is excludeã in the
final analysis.
(v) Remaining outliers
(vi) Snowmelt
Although snowmelt is not an important flood-producing
mechanism in New Zealand, when it combines with
rainfall it may cause floods greater than would occur
through rain alone. However, snowmelt catchments do
not appear aniongst the catchments listed earlier as
outliers. Although data on the extert, depth, and
water-producing capabilities of snowpack are sparse in
New Zealand, it is known that in the Fraser catchment
(Station 75259) five of seven annual flood maxima
us€d in this study occurred in October, November or
Decernber, and are likely to have been associated with
snorvmelt. This may account for any underestimation
of Q for this catchment (residual error equal to 0. 16).
Snowmelt may also be a contributory factor to the
underestimation of Q for other catchments in the
island, paticularly 71116 (Ahuriri at South Diadem)
and75276 (Shotover at Bowens peak).
The final estimation equations were derived after shifting
the boundary between the West Coast and Inland Marlborough/Canterbury
regions slightly lo include the catchment
for Station 64ó06 in the West Coast region, and excluding
Stations 65902, 68806, 71122,74314 and 9ll0l for the reasons
stated.
4,5.4 Final equations for South lsland
estimate is decreased compared with the first trial equations
in Table 4.5.
The geographic distribution of residual errors for the fin_
4.7. Yery good fit has been
Inland Marlborough/Cantrs
are +0.22, and their disdom.
The fÏt for the W€st
Coast and Inland Otago and Southland regions is satisfactory;
one error exceeds 0.30 and t$¡o more exceed O.A.
Although most errors appear randomly distributed in
sDace, several positive errors clustered in the southern part
of the Inland Otago and Southland region suggest ihat
some consistent underestinnation of Q has occuried there.
Table 4.7 correration malrix for rogs of North rsrand charact€rist¡cs.
o
AREA
MARAIN
t224
LENGTH
FOREST
STMFCY*
s1 085*
€LEVT
1.OOO
o.830
o.294
o.2ö7
o.815
o.342
-o.117
-0.413
o.247
AREA MARAIN LENGTH FOREST STMFCY. S1085. ELEV'
1.0O0
o.040
-o.110
0.944
0.189
-o.121
-o.576
0.303
l.OOO
0.296
o.o44
0.506
o.o69
0.332
0.454
l.OOO
-o.101
o.312
o.o60
o.o09
-0.149
l.OOO
0.191
-o.187
-0.598
o.278
1.000
o.178 l.OOO
o.o77 o.196
0.348 o.157
l.OOO
0.348
l.OOO
¡ lncomplete Sample
&
Water & soil technical publication no. 20 (1982)

West Coast
õ= 0.0233 AREAeo I;?
(R2=.la , se=0'148)--'
I n land Marlborougþ/Canterbury
õ = O'9ó4AREAo'88
(i2=o're , se =Q'lQP|
Mackenzie, lnland Otago, Southland
õ=o.ootgAREA:to Ill,
(.R2= o.rs, se =o.r4ó)"-
East Coast
õ = t. n x lo-ten¡Ätt¡nmAlN3'o
(n'= 'ra , se=0.il7)
Nole: R= Multiplle correlotion coefficient
se= $1q.¿.rd error of estimote for
logorithms
Water & soil technical publication no. 20 (1982)
Fþu]|'4.TLogarithmicresidualerrorsforfinalsouthlslandregionalequations'
65

I
++
++
*
E
4.6 Analysis of North lsland data
4.6.1 Preliminary analysis of data
10 100
[otchmenf Areo ( kmz)
Figure 4.8 O vs AREA, North lsland catchments.
a : 1.87 AREA o sr
(R': = 0.69, se = 0.442)
44
As with section 4.5 the object of this section is to devise
estimators of Q ttrat are better than Equation +.+ Uy using
variables besides AREA, and by choosìng a number of re_
grons.
Stepwise regression results
_
for all 97 stations are tab_
ulated in Table 4.8. The best fit equation obtained is
a = 1.37 x l0-'AREA1 t3l2z4t,EeMARAIN¡ o?
(R'? = 0.81, se = 0.348)
45
Examinati
errors from
which berter
followed is s
tion of residual
it ïå'å:ì#i
and.
4.6.2 Development of trial regional estimators
tween MARAIN and 1224 (0.30 compared with 0.75). phys_
ically this may be a reflection of the sparseness Water òf & the soil net_ technical publication no. 20 (1982)
66

Table 4.8. Stepwise regressions for all North lsland data.
No. Var. Name
Coef
br
se
of coef
R2
se
est
Const
log a
Multiplier
a
1
2
AREA
AREA
t224
AREA
t224
MARAIN
o.81
0.84
2.33
o.83
1.89
1.O7
o.o56
0.048
o.377
o.045
o.368
o.270
14.5
17.7
6.2
18.6
5.1
4.O
0.829
o.882
o.900
o.687
o.778
o.810
o.442
o.372
o.348
0.271 1 .87
-4.263 5.46 x 1O-õ
- 6.862 1 .37 x 10'
Table 4.9 Stepwise regressions for first trial North lsland regions
Region
Number Variable
Variables Name
Coef
b'
se
of coef
R2
se
est
Const Mult¡plier
loga a
Non-Pumice
(84 catchments)
1
2
AREA
AREA
t224
AREA
t224
MARAIN
o.74 0.049
o.77 0.037
2.13 0.271
o.76 0.034
1.77 0.262
0.78 0. 1 91
'15.2 0.861 0.74 0.341
20.7 0.925 0.86 0.257
7.9
22.4 0.939 0.88 0.234
6.8
4.1
0.507 3.21
- 3.63 2.33 x 1O-a
- 5.49 3.24 x 1O-o
Pumice
( 1 2 catchments)
1
2
AREA
AREA
t224
AREA
t224
MARAIN
o.84 0.22
0.90 0.11
3.88 0.64
o.79 0.o9
2.41 0.73
1.74 0.64
3.8 0.765
8.5 0.958
6.1
8.9 0.978
3.3
2.7
o.59 0.359 -O.310 0.490
O.92 0.168 -7.806 1.56 x 1O-8
0.96 O.142 - 10.36 4.39 x 1Oi1
of which catchments lay within it, presented difficulty.
Several catchments (for example 9101, Waitoa; 21803,
Mohaka) have their headwaters in this pumice country, but
most of their areas lie outside the pumice region. Others
(e.g., 15410, Whirinaki) are mainly pumice but have a substantial
area outside the region. In still other catchments
(those lying mainly on the slope of the central North Island
volcanoes) the mantle of soil over rock is minimal and its
hydrological influences were not known. After several
trials, the pumice region was defined as comprehending
three of the hydrological regions set out by Toebes and
Palmer (1969). These were Taupo Pumice, Taupo Rhyolite,
and East Raetihi which made up a discontinuous region including
a total of 13 catchments, seven tributary to the
Waikato River, four draining to the Bay of Plenty, and two
tributary to the Wanganui River. Closer inspection of the
data for these l3 catchments showed that 11432108 (Purukohukohu)
was a distinct outlier in having the smallest
catchment area and the least Q (by almost two orders of
magnitude) for all 97 North Island catchments. For this
reason, and because it was ephemeral, it was excluded from
subsequent analyses.
Taking two regions, pumice and non-pumice, trial regressions
were undertaken. Stepwise results are given in
Table 4.9 and the distribution of residual errors for the best
fit equations is shown in Figure 4.9. This figure shows that
within the pumice region the residuals seem randomly distributed
with generally low values, but the remainder of the
island contains very large residuals, some exceeding I 0.50.
The southern part of the island including tributary catchments
to the lower Rangitikei, all the Manawatu, Wairarapa
and Wellington area catchments, have, with one small
exception, positive residuals meaning that Qo5, for this area
is underestimated. Similarly, positive residuals occur over
much of the Northland and Auckland areas. The fact that
tropical cyclone events tend to produce flooding in this
area, and also the Coromandel and East Cape areas, may
be a tentative basis for a region including these areas. Negative
residual values occur in the central part of the island
outside the pumice region. This suggests a division of the
Water & soil technical publication no. 20 (1982)
island into four regions, and if the central part is divided
between east and west coasts, into five regions, whose tentative
boundaries are drawn dashed on Figure 4.9. These
five regions are taken as a basis for further study.
A number of trials were undertaken with these regions to
determine where boundaries should be placed. Catchments
which appeared as outliers were checked, both for the correctness
of data and for any features of the catchment
which might influence flood peaks. Seven of the larger residuals
could be attributed to special conditions of the catchment
and were excluded from the final analysis.
These were as follows:
(i) C¡tchments with large ponding effects
Serious over-estimates were made for Q for 9l0l
(Waitoa) and 9108 (Piako). Two possible causes for
this are, firslly that the headwaters for these catchments
lie in the pumice region, and secondly that the
catchments have amongst the lowest channel slopes of
all the North Island catchments, and have a very flat
topography with peaty soils and swamps in the lower
reaches. This second factor also causes attenuation of
flood hydrographs. Thus these two catchments were
excluded frorn further analysis. Others having large
negative residuals in Figure 4.9 were 33307 (Wanganui
at Headwaters) and 1143428 (Ohote); these also were
excluded on the basis that large parts of the catchments
are swamps.
(ii) C¡tchment in l¡mestone area
Catchment 40703 (Mangakowhai), which drains Waitomo
limestone country, also had a large negative residual
and was subsequently excluded on the basis that
the catchment topographic area may not be the true
catchment area.
(iii) Catchment with short record
Catchment 39508 (Manganui) had only four years of
record. It was excluded on the basis that the estimate
of Q may have excessive sampling error.
67

Non Pumice =
õ = 3-24xto'6 AREA'7ó lr,o''" MARA|No'78
( R2= 9.g3,- se= 0.228 I
Pumice
[ = a.39 ^
ro ll AREATe \r1'^' MARATNI'24
( R'= O'9ó , se
= O.lO5 )
Figure 4.9 Trial North lsland regions.
68
Water & soil technical publication no. 20 (1982)

ln the trials undertaken for the provisional regions
shown dashed in Figure 4.9 both 13901 (Mangawhai) and
15534 (Wairere) showed as outliers in the regions to which
they were initially assigned. As they fitted best into the
adjacent pumice region, they were placed there for the final
analysis. This required extension of the pumice region into
the coastal Bay of Plenty area; in terms of the hydrological
regions of Toebes and Palmer (1969) it includes Tauranga
and Opotiki regions. This assignment is tentative because
the soils in these catchments are not pumice to the extent of
others in the Rotorua/Taupo area. Their better fit with the
pumice region could be the result of inaccurate rainfall intensity
statistics.
4.6.3 Final equations for North lsland
Table 4.1O Stepwise regressions for final North lsland regions.
After a number of trials, final equations were developed
for the regions shown in Figure 4.10. The stepwise regression
results are givern in Table 4. 10. In all but one case the
best fit equation includes AREA and one or two of the
rainfall statistics. The exception is the Manawatu/WairarapalWellington
region were the equation including AREA,
1224 and FOREST provides a very good fit. However,
when MARAIN is substituted for FOREST in the equation
it is almost as good; this is preferred as it should provide a
more robust estimator. The table shows that for every region
the accuracy of estimate can be improved by including
a rainfall statistic in addition to AREA, and also, that other
catchment parameters with the possible exception of FOR-
EST in one region are not of importance. It is possible that
FOREST does not directly influence flood size; rather it
does so indirectly to the extent that correlations occur between
FOREST and the rainfall statistics (Table 4.7). For
the Manawatu/Wairarapa/Vr'ellington region where FOR-
EST was most dominant in these regional equations, the
Region
Northland/
Coromandel/
East Cape
{21 catchments}
Pumice Land
( 1 4 catchments)
East Coast
(1 1 catchments)
Manawatu/
Wairarapa/
Wellington
( 1 9 catchments)
West Coast
(25 catchments)
Number Variable
Varìables Name
1
2
1
2
1
2
1
2
AREA
AREA
MARAIN
AREA
MARAIN
ELEV
AREA
MARAIN
ELEV
LENGTH
AREA
AREA
t224
AREA
t224
MARAIN
AREA
t224
MARAIN
FOREST
AREA
AREA
t224
AREA
AREA
FOREST
AREA
FOREST
t224
AREA
t224
MARAIN
AREA
AREA
t224
AREA
t224
MARAIN
AREA
t224
MARAIN
FOREST
Coef
bl
se
of coef
R2
SE
est
o.70 0.06 10.8+ 0.927 0.86 0.237
0.64 0.o3 19.5* 0.983 0.97 0.1 19
2.33 0.31 7.6*
0.62 0.o3 18.7* 0.986 0.97 0.1 10
2.O1 0.33 6.2*
o.22 0.11 2.O
o.84 0.16 5.2* 0.988 0.98 0.107
2.O3 0.32 6.4*
o.21 0.11 2.O
-o.39 0.28 -1.4
Const Multipl¡er
loga a
0.807 6.42
-6.66 2.18 x 10'+
- 6.OB 8.24 x 'l O-7
-6.06 8.71 x 1O'
0.67 0.12 5.5* o.a44 0.71 0.348 0.0933 1.24
0.83 0.06 13.5* O.971 O.94 O.161 -7.94 1.15x1O-8
4.O2 0.60 6.7*
o.74 o.06 12.2* 0.984 O.97 Oi2A - 10.51 3.Og x 'l O{1 +
2.54 o.72 3.5*
1.75 0.64 2.7 *
O.88 O.O9 9.9* 0.989 O.98 O.111 -11.94 1.15x1O{'?
3.16 0.70 4.5*
1.80 0.56 3.2*
-o.17 0.o9 -2.O
o.80 0.o8 10.6*
0.76 0.o3 27.4*
2.24 0.29 7.8*
0.90 0.1 3 6.9*
o.72
0.46
o.82
1.53
o.94
0.06 12.2*
o.o5 8.9-
o.74 0.o4 16.7*
o.34 0.o5 6.7*
1.22 0.33 3.7*
o.o5 15.8*
o.19 4.O*
o.39 4.9*
o.85 0.o8 1 1.3*
o.az 0.o5 16.7*
2.18 0.38 5.8*
o.82 0.o5 17.7*
1.67 0.44 3.8*
0.78 0.39 1.9
o.79 0.o5 16.1 *
1.6'l O.42 3.8*
0.80 0.37 2.1
0.1 1 0.06 1.8
0.963 0.93 0.227
0.996 0.99 0.082
o.858 0.74 0.341
0.978 0.96 0.144
0.988 0.98 0.107
0.982 0.96 0.1 18
o.974 0.95 0.157
0.977 0.96 0.1 50
0.296 1.98
-4.O5 8.84 x 10{ +
0.232 1.70
o.1 58 1.44
-2.O5 8.99 x 1O-"
-5.51 3.12x10-6 +
0.920 0.85 0.258 0j82 1.52
0.969 O.94 O.1 67 - 3.83 1 .48 x 1O-1 +
- 5.41 3.87 x 10-6
-5.51 3.13x10-6
* significant at 5olo level
+ preferred equation
Water & soil technical publication no. 20 (1982)
69

Northlond f C"ro^ondel f Eost Cope
ö = 2.18 x lo z tRtlo'ó4 MARAIN2'33
( R'= O'97 , se
= O.ll9 )
West Coost
_Á
Q = l.48xlO '
( R2- o.94 ,
AREÁ t' \r1''"
se
= 0'167 )
Eost Coost
õ g.g4 7ó
= x lo-saREAo
\rl'ro
Pumice
( R2= O.99 , se = 0.082 )
õ = 3.o9 x td't' IREA.''o lrrl- t',
MARAT N
( R'= O.97 , se = O-nB )
Monowotu /Woiroropo / Wellington
Q = s.ts * ldo t" RREA' Irr''t MARAIN o'e1
(R2=9.96 , se=O.ll8 )
Figure Water 4.10 & soil Final technical North publication lsland regions. no. 20 (1982)
70

correlations between (logs oÐ FOREST and 1224, and
FOREST and MARAIN were 0.90 and 0.65 respectively;
this was one region where estimates of l2?A were suspected
to be unreliable.
The preferred equations of Table 4.10 are shown in Figure
4.10 with their appropriate regions, and also the residual
errors for logarithms. In general the equations seem
more reliable in the north and east of the island, a situation
also noted in the South Island. The distribution ofresiduals
generally appears reasonably random in space. The region
for the West Coast includes a number of catchments tributary
to the Wanganui River and a number originating on
the slopes of the central North Island volcanoes. Many of
the larger residuals for the island are clustered here, presumably
because of the variety of soil types, including pumice,
and the sparse coverage of rainfall intensity measurements.
The equations for the East Coast and West Coast regions
suggest that they should be combined into one, but
doing so resulted in regional biases. Hence the separate regions
should be maintained.
4.7 Discussion of results
The equations derived in sections 4.5 and 4.6 are intended
for application to rural catchments where flood
storage is not excessive or where other dampening effects
are not dominant. All the nine regional equations use catchment
area, and all but one use area and one or two of the
rainfall statistics; other physical catchment characteristics
used in this study appear to be of little consequence. This is
an important finding, since results obtained in overseas
countries (see section 4.8) have suggested that these other
physical characteristics are relatively important. The
dominance of rainfall statistics is possibly due to the
generally steep nature of New Zealand catchments (see section
4.8). The two sets of rainfall statistics considered in the
study have a large range of values; both cover more than
one order of magnitude in the South Island, though the
range is less in the North Island.
Since this study was completed, an updated analysis of
rainfall intensity data has become available (Tomlinson
1980; Coulter and Hessell 1980). Tomlinson used 16000
years of data from 940 manual daily raingauges and 3500
years from 180 recording raingauges. Comparison of revised
1224 estimates with those from Robertson (1963) for a
sample of 87 stations did not reveal statistically significant
differences. This suggested that the revised estimates may
also be used for estimating 1224. Sirce the revision used
more than twice the number of stations, more accurate estimates
of 1224 lor individual catchments should be possible.
For convenience, revised 1224 estimates for the 94O daily
gauges used by Tomlinson are included as Appendix D.
- The revised intensity data were also mapped by Tomlinson.
However, in high altitude areas, especially along the
Southern Alps, use of the mapped values is not recommended.
In mapping, rainfall is assumed to increase with
altitude, This increase was not allowed for when catchment
estimates for l2A were made, so the maps will give catchment
estimates of 1224 greater than the estimates used in
deriving the equations for Q. Thus inflated Q estimates
may result from
The 2-year rec
uration intensitY
estimated from
auges was used
principally because of the better national coverage of daily
iead manual gauges for observing this duration rainfall
compared with shorter duration rainfall statistics estimated
from automatic rainfall recorder data.
As noted in section 4.4, estimates of catchment mean annual
rainfall have a low accuracy for many South Island
and this is possibly why inclusion of mean annual rainfall
improves the estimate in three of the five North Island regional
equations.
Little can be saicl of the physical significance of the exponents
for the regional equations. Whilst values of the intensity
exponent around unity for two of the South Island
regions might have some physical interpretation, the meaning
of exponents of the rainfall statistics which exceed 2.0 is
unclear, even though their statistical significance is undoubted.
Obviousl),, in using the equations, particular care
must be given to the estimation of rainfall statistics, because
estimates outside of the range of the values of the
sample used in developing the equations could result in
severe errors in estimates of Q. Tables 4.1 and 4.2 are a
guide to typical valtues of the rainfall statistics.
Where a catchment lies near a regional boundary and
each regional equation gives different estimates, the precise
location ofthe boundary is bound to create difficulties. For
some regions, dominant flood-producing weather patterns
are thought to apply, and a decision about which region a
catchment fits into could be based on the weather conditions
which are believed to produce the most flooding.
An example is a number of Marlborough and Canterbury
rivers in the Inland region, where the flood-producing
weather conditions are possibly southerly. Their headwaters
near the divide flood in nor'westerly weather condi
tions and fit in the West Coast region. The rivers flow
through the East Coast region where flood-producing weather
patterns are thought to be easterly.
In the case of the North Island Pumice region, catchments
have been included where pumice was thought to
have a dominant influence on the flood hydrology, but two
coastal Bay of Plenty catchments were tentatively included
here because this was where they fitted best, even although
pumice is not dominant on these small catchments. rÙVithin
the Pumice region, there appears to be a gradation in the effect
of the pumice. For instance, pumice lies to great depths
on the Kaingaroa Plateau within which much of the catchment
of the Rangitaiki River lies. The 28 years of record for
this river at Murupara (AREA : ll84km', Station
15408), but which was not used because it exceeds
ll00 km', gives_a Qous : 41.6 m'/s but the estimate from
the equation is Q"rt = 202 m3/s, representing a residual error
of - 0.69. Clearly, the dampening effects of pumice are
severe in this case.
The annual flood regions delineated in this chapter are'
in general, very similar to the flood frequency regions defined
in Chapter 3. An exception to this is in the eastern
area of the South Island (see Figure 4.7). From a design
characteristics, on the other hand, is also concerned with
the coefficients of variation and skewness of the flood record,
and these can be regarded as the slopes and curvatures
respectively of the individual dimensionless-magni-
Therefore it was not unexof
the flood frequencY chargions
that differed in Places
from the set deveioped for estimating Q.
4.8 Compar¡son with other results
Similar equations
given in Table 4.ll l.
favourably in terms
ent of determination
this needs to be balanced against the use of a relatively
small range of catchment areas (0'2 to ll00 km'); poorer
fits may be obtained if larger catchments are used' The
other notable feature of Table 4'll is the range of expon-
estimated with reasonable accuracy for the North Island, ents for AREA. The values tend to be less than the values
Water & soil technical publication no. 20 (1982)
7l

Table 4.11 Comparable equations for other countries,
Est¡mat¡ng eqn R2 SC
est
Region
Area Range (km,)
Min. Max.
Reference
o
o
= 0.56 1 AREA 8s
: 0.0765 AREAi o€ S1O85o s' o.841
o.922
o.1 94
o.142
New England
New England
: 2.42 AREA ss
Texas and Sthn
= o.o589 AREA 68110241 New Mexico
50
250OO Benson ('l 962b)
90000 Benson (1 964)
O :a AREAb
0.267

Pooled
Pooled
Poo led
Cy = 0.98
Cy = O'óó
Cv = o'3ó
Figure Water 4.11 & soil Distr¡but¡on technical publication of Cv of annual no. 20 maxima (1982) for South lsland stations'
73

Poo led
cv
Pooled
o.40
F¡guro 4.12 D¡stfibut¡on
Water of & cv soil of technical annuar maxima publication for North no. 20 rsrand (1982) stat¡ons.
74

Draper and Smith 1966). ln our case, the true value of the
dependent variable Qnu. is not known with certainty. It is
subject to time sampling error and can only be estimated
from the period of flow record available. The relative magnitudes
of time sampling errors are indicated by the pooled
Cy values in Figures 4.8 and 4.12.
A second difficulty is that within a region some adjacent
catchments may be subject to the same storms of large areal
extent and a pair of series of annual maxima for such catchments
is likely to be cross correlated: errors in estimates of
Qo6, will therefore not be random, but will also be correlated.
In this situation regression analysis is still permissible,
but estimation of the prediction error is more complex.
An analysis of the situation is provided by Matalas
and Gilroy (1968), and some practical examples are given
by Hardison (1971).
When a regional regression of log'o Q is calculated on a
set of m catchment parameters, the standard deviation of
the log,o Q about the regression expressed in log,o Q units
is denoted by Sp. lf these deviations of the log,o Q from the
regression are normally distributed, then the coefficient of
variation of the untransformed Q about the regression, C¡,
is given by
Cä = .*p (2.303 SR)' - I 47
When Q is estimated from a flood record that is N years
long, and the coeffìcient of variation of the annual maxima
is denoted Cy, the estimate of Q will differ from the population
value (that would be obtained from a very long record)
with a coel'ficient of variation of CylN.l.
ci : ci /N"
When Q is predicted using the regional regression it will As the quantity Nu could provide a useful guide for using
differ from the population value, and the coefficient ofvar- the regression equations, it is evaluated for each of the reiation
of the difference averaged over k sites, denoted by gions together with Cp for each region (Table 4.12). Esti-
Table 4.12 Prediction errors and equivalent lengths of record.
Cp, is calculated from Equation 4.8, which is derived from
Hardison (1971).
c'p : ch(t - + -
tf+-, ) + ci (2q - r)/N6..... 4.8
where p is the average cross-correlation between annual
maxima series from pairs oi catchments in the region, and
Nç is the average length of record. When there are many
uncorrelated records such that sampling errors tend to cancel,
and the average record is short (k large, p small, N6
small), then Cþ can be less than CilNc, so rhat a better
estimate is obtained from the regression at a site than from
the record at a site.
Note that Cp is an average prediction error, and will
over-estimate errors on predictions for ungauged catchments
whose parameters are near the mean value used in
calculating the regression, and conversely. In New Zealand,
no estimates ofthe interstation correlation coefficient q are
available, but typical values may reasonably be expected
within the range 0.2 to 0.8. Three values of p (0.2, 0.5 and
0.8), were therefore used in evaluating Equation 4.8.
Given the coefficient of variation of the prediction error
Cp, ân estimate can be made of the length of record necessary
to estimate Q with the same degree of accuracy as is
given by the regression equation. If Nu is this equivalent
length of record, anLd the prediction error is expressed as a
percentage, then
49
Region S¡
(for regression
of logarithms)
Cvkm
(no. of (no. of
stations) regression
variables)
Nca
(av length
record)
cR cP
(Eqn 4.7) (Eqn 4.8)
l"l,\ l"/"1
N, Typical
(Eqn 4.9) Nu
(yrs)
(yrs)
Northland/
Coromandel/
East Cape
Pumice
East Coast Nl
Wairarapai
Manawatu/
Wellington
West Coast Nl
West Coast Sl
o.119
o.128
0.082
o.118
o.1 67
0.148
o.54
o.54
o.54
o.40
o.40
0.36
21
14
t1
19
25
t9
1 1.6
12.O
13.O
13.5
110
9.4
o.2
o.5
0.8
o.2
o.5
o.8
o.2
0.5
o.8
o.2
o.5
o.8
o.2
o.5
o.8
o-2
0.5
o.8
27.9
21 .9
27.9
29.9
29.9
29.9
1 9.1
1 9.1
1 9.1
27.7
27.7
27.7
39.9
39.9
39.9
35.O
35.O
3 5.O
27.5
30.1
32.5
33.7
35.8
37.7
19.4
22.6
25.4
30.0
31.1
32.3
41.6
42.6
43.6
37.1
38.1
39.3
39
3.2
2.3
2.6
2.3
2.1
7.8
5.7
4.5
1.8
1.7
1.5
o.9
o.9
0.9
0.9
o9
o.8
lnland
Marlborough/
Canterbury
East Coast Sl
Mackenzie/
lnland Otago/
Southland
o.1 09
o.1 05
o.146
0.66
o.98
o.66
13
1'l
'I 5
18.0 0.2
0.5
o.8
8.4 0.2
o.5
o.8
89 02
o5
o8
25.O
25.O
25.O
24.5
24.5
24.5
34.5
34.5
34.5
24.4
27.2
29.8
12.5
29.O
39.1
34.6
38.6
42.2
7.3
5.9
4.9
61.6
11 .4
6.3
3.7
2.9
2.4
Water & soil technical publication no. 20 (1982)
75

mates of Cp typically range between 2OVo and 44go for different
regions. They are generally somewhat greater than
Cp, and are generally not greatly influenced by the values
assumed for p.
Values estimated for Nu given in the right-hand column
of Table 4.12 range from one year for the West Coast of
both islands to about seven years for the East Coast of the
South Island. Such results are in accord with intuition.
Where the Cy is low_(as on the West Coast) a reasonably accurate
estimate of Qo5, may be obtained from a relatively
short period of rec
on
is of limited valu
is
greater, a longer
to
estimate Qo6. with
on
equation estimate, and the regression equations may be of
greater utility.
tühere only a short period of record is available for a site
for which a design flood estimate is required, a decision
var (Q)
weights for combin
in a best estimate. If
its variance can be e
_l
var (Qo6.)
I
var (Q.,x)
4t0
4.11 Summary
_ The country was divided into nine regions lbr estimating
Q using regression analysis. The physical justification lor
these regions was discussed. Apart from the south of the
South lsland, the study used a good distribution ol catchments,
and the range of values covered for Q, area, and
other parameters was very large.
The results demonstated that generally catchment area
and the rainfall parameters considered are sufficient to predict
large differences in flood magnitudes within the nine
regions delineated and that the other physical characteristics
used for the catchments do not improve that prediction.
Apart from the Southern Alps of the South lsland,
the mean annual rainfall can be estimated with reasonable
confidence from isohyetal maps. Rainfall intensities were
estimated from data available in Robertson's (1963) publication.
Updated intensity data are now available (Tomlinson
1980; Coulter and Hessell 1980) and, with more extensive
intensity information, better estimation equations are
anticipated.
Preliminary results of the study enabled identification ol
catchments which did not fit into regional trends. Where
reasons for anomalies could be identified, the catchments
were excluded from the final analyses since their inclusion
could have led to biased results. About 790 of catchments
were in this category. Designers should be aware of factors
likely to modify flood peaks and if in doubt seek specialisr
advice.
16
Water & soil technical publication no. 20 (1982)

5 Application
5.1 lntroduction
This chapter collates the applicable results and findings
from the preceding two chapters and formulates them into
what is subsequently reierred to as the Regional Flood Estimation
(RFE) method. Rules for the applicability of the
RFE method are given, a design strategy for estimating the
T-year flood peak is suggested and a number of examples
are given which demonstrate the use of the method.
The RFE method is intended as a procedure to be used
for estimating design flood magnitude in situations where
insufficient flood records are available for conventional
fiequency analysis. It is one of several design flood estimation
methods in such situations and other methods should
be used and compared with it. It has been derived from
tlood records by:
(¡) defining regional flood frequency curves of Q1/Q vs
T, where Q1 is a design flood with return period T and
Q is the mean annual flood; and
(ii) developing a set of equations for estimating Q based
on catchment area and measures of rainfall.
A comparison with Technical Memorandum No' 6l
(TM 6l) is reported in Appendix E.
5.2 Applicability
The applicability of the RFE method is necessarily constrained
by the restrictions that were applied to the data
used in deriving the method. The following constraints
therefore apply.
The method should only be used for rural catchments.
The method should not be applied to catchments in
which snowmelt, glaciers, springs, lake storage or
ponding significantly affect the flood peak characteristics.
The ranges of catchment areas for which the regional
flood frequency curves and the regional mean annual
flood equations were derived are listed in Table 5.1.
These are a guide for the size of catchment to which
the method should be applied.
Because of the subjective and rather broad definition of
regional boundaries, it is suggested that, for catchments
near boundaries, floöd frequency curves and annual flood
equations for the regions either side of the lines.should be
used in estimating Q1/Q and Q respectively. As in a design
situation where different methods yield different estimates,
the different Q1/Q and Q estimates then need to be 'compared',
i.e., the merits of each should be assessed and the
choice of an estimate should be made after a rationalisation
of the relevant facts. Alternatively, a belief probability can
be attached to each estimate and their expectation calculated,
which is akin to taking a weighted average of the estimates.
5.3 Design Strategy
5.3.1 General
The strategy for the use of the RFE method in design is
dependent on two main factors: N, the length in years of
the flood record if a record is available, and T, the design
return period. The influence of these factors on the two
parts of the RFE method (i.e. the regional mean annual
flood equations and the regional flood frequency curves) is
explained in the two following sections and summarised in
Figure 5.1 .
5.3.2 Estimat¡on of O
(¡) N(Nu
Where there is a flood record and its length N is less than
Nu, which is the
is equivalent to the
prãcision of the r
on (see Table 4. l2)'
the mean annual
imated from the regional
equation and the available flood record. In applying
the equation it is particularly important to estimate values
for the rainfall variables 1224 and MARAIN in a similar
manner and from the same data base as used in the equation's
derivation. Specific points to note in estimating
values for 1224 and MARAIN are outlined below.
1224 Estimates ol the 1224 rainfall intensity statistic used
in deriving the equations for Q were obtained by taking the
arithmetic mean of the 2-year 24-hour data listed by Robertson
(1963, Table 9) for rainfall stations located within,
or near to, the catchment concerned. Estirrates can be
made from the tabular results (Appendix D) obtained by
Tomlinson (1980) in a recent revision of the frequency an-
Table 5.1 Ranges of catchment areas used to derive regional flood frequency curves and mean annual
flood equations.
Flood frequency
reglon
(Fis. 3.6, 3.7)
Combined N.l.
West Coast
Central Bay of PlentY
N.l. East Coast
Central Hawke's Bay
S.l. West Coast
S.l. East Coast
South Canterbury
Otagoi Southland
Catchment area
(km2)
(Table 3.2)
fntn max
2.5 6643
28.2 2893
171 2370
24.3 2424
48 6350
74.6 3430
22.4 899)
lo9
)
18321
Mean annual flood
feglon
(Fig.4 7,4.1O)
Northland/Coromandel/
East Cape
West Coast
Manawatu/WairaraPa/
Wellington
Pumice
Northland/Coromandel/
East Cape
East Coast
West Coast
lnland Marlborough/
Canterbury
East Coast
(Mackenzie, lnland
(Otago, Southland
(East Coast
Water & soil technical publication no. 20 (1982)
Catchment area
(km')
(Tables 4.1, 4.2)
min max
o4 640
3.1 1075
9.4 734
2.6 534
o.4 640
o5
997
4.O 998
o.2 1070
2.2 464
36.8 1088
2.2 464

-J
æ
'll
o Eo
!¡
Assemble llood prák dåta
lncludlng âll hletoslcat
flood ln?ornatlon.
lrha¿ lr th. I.ngÈh N of th. evallsblr flood rscord?
.õ
-3
J
!
o
{
o t
o
f
o*æ
o
CL
o
2.
c¡ f
Øñ
o
@
c
2.
f
(o
è
o
Ðo
e.
o
to,
f!
o
cl
m
ø
d.
:t
0t
4.
o
f
o ê
, oo.
Apply the Generallsed Curve
Esttnato0arauelghtad
o? tho âstlnãtls fron3
I Calculating th€ n€an ol
avall¿ble annual serleo (
graphically interpolatlng
0¡.¡¡ fron an histo¡ical
:cri ee )
2 Applylng the roglonal
squation
Ooes I
exc.ed th! llnlt
of th6 Rsglonal
Cu¡ve?
obtaln 0t snd
det€rñiñs the stãndg¡d
arror ol oltlnata
NsNu
Apply the RBglonåI Cu¡ve
N>Nu
E¡tlnate D ¡¡ th¡ arlthfr.tlc
taån o? th¡ annual ae¡L¡s
fo¡m e frequency anelysia ui
tuo-Farsm6tsr distributioñs
except for sitEÊ j.n rhe South
CanteEbuDy snd 8ay of Plsnty
flood l'¡6au€ncy rBgioñs. uhers
I.
hl6torlca¡ ftood p.ak
infq¡ñatlon 6våilablo
Is
N ¿20
o!
1>100
?
EeÈlnate õ uy grephic;Ily
lnt!¡pol3t¡ng Ê¡.¡¡ frm
th. historlcal s.¡l3s
Perforn a frequgñcy enalysis
ulth tuo and th¡3e-paranrtsF
di BtriSuti,oñ3
ConpBr€ ths frsqu6ncy analyale rs6ult! uith ths rstinatr
obtafn€d from the R€gional Curv¡ (o¡ the Gener€lla6d Curva
\¡hen I excs€ds the reglonaÌ curve llnlt) ônd obtðin
s uelghted flood p.!k ..tlnatr' .Epeclslly ll I > 2N
Water & soil technical publication no. 20 (1982)

alysis of the country's rainfall intensity data. As this revision
used data for twice the number of stations used by
Robertson, more accurate estimates of 1024 for individual
catchments should be possible using Tomlinson's results.
Note that an areal reduction factor should not be applied
to an 1224 estimate. Further, the rainfall stations used in
the estimation of 1224 should not necessarily be the nearest
but should be the ones that record weather patterns that are
of most relevance to the catchment.
In the Southern Alps, Tomlinson's (1980) maps of rainfall
intensity assume that the intensity increases with altitude.
This increase was not considered in the estimates of
1224 used to obtain the regional mean annual flood equations.
Thus the use of the estimates of rainfall intensity in
the equations may lead to overestimates of Q for catchments
running into the Southern Alps. Therefore, when
calculating 1224, poinr estimates of intensity should be
averaged for the raingauges which receive rainfall typical of
that for the middle and lower parts of the catchment.
MARAIN The mean annual rainfall for a catchment may
be estimated directly from rainfall records for stations
within, or near to, the catchment. Where only short rainfall
records exist, or where there are none, estimates of
MARAIN should be obtained from the l:500 000 isohyetal
maps of l94l-1970 annual rainfall normals published by
the NZ Meteorological Service.
When there is at least one year of flood record available,
we suggest that both the available record and the regional
equation be used to obtain separate estimates of Q. These
estimates can then be combined to form a weighted average
estimate of Q , with the weighting of the Q value estimated
from the record being based on the length ofthe record relative
to Nr. Hence, for example, if N : 3 and N, : 4' the
weighting factors for the estimates taken from the record
and regional equation should be
3/'7 lì.e.
(ii) N > Nu
NN
N+Nu
N*N,
When the flood record length exceeds N' Q may be estimated
as the arithmetic mean of the annual series. It could
also be estimated f¡om a partial duration series (NERC
1975, pp. 185-213) when N is less than l0 years. In the case
where an outlier or historical flood peak Q."* occurs in an
annual series such that Q*"*/Q.e¿ ) 3, it is suggested that
Q be estimated graphically from a probability plot of the
annual series as the flood peak with return period T : 2.33
years.
more flexible frequency curves, it was found in the evaluation
tests (Appendix A) that a two-parameter distribution
gives a good approximation to a three-parameter one up to
T : 100 and that it can give more sensible results, even
though it may not produce quite as good a fit to the annual
senes.
(iii) N > 20
V/ith a flood record of 20 or more years in length, both
two- and three-parameter distributions should be fitted to
tbe annual series for the estimation of Qr ' A visual inspection
of the goodness-of-fit of the distributions to the series
should then be made and a distribution chosen for estimating
Qr . When it is difficult to decide between two or more
fitted distributions, the Q.¡ estimate should be determined
by averaging the estimates given by these distributions.
In applying frequency analysis methods to estimate a design
flood peak Qt, care should be taken to ensure that
they are not grossly extrapolated. For example, if N < 20
and the two-parameter EVI distribution is fitted to the annual
series, its extrapolation past T : 100 years for catchments
in some of the eastern regions, e.g' South Canterbury,
may lead to an under-estimation of Q1.
It is recommended that the fitted distribution should not
be extrapolated beyond a return period T : 5N' This limit
is less stringent than those often recommended in other
tests (e.g. a limit of T : 2N is suggested (ICE 1975) for the
NERC (1975) study) and extrapolation beyond it is unwise
on the basis of present evidence. The safest course of action
when T exceeds the extrapolation limit is to use the regional
curve, or the appropriate generalised curve when T exceeds
the upper limit of the regional curve.
Finally, when the record length N is sufficiently great to
warrant the performing of a frequency analysis, the resulting
Q1 estimates should be compared with that using the regional
(or generalised) curve, with Q being calculated from
the annual series. A, decision must subsequently be made as
to which estimate to accept for design. This may involve
taking a weighted average of the estimate from the frequency
analyses of the site data and the estimate obtained
using the regional curve, and this procedure is suggested
when T > 2N. In making this decision on the final Q1
value it should be lemembered that variations are inherent
in all flood records, especially small ones, so that the trend
in the probability plot should not be over-emphasised, even
though it may depart significantly from the regional one.
Instead, the emphasis should be placed on the regional
curve, for it represents the trend of all the flood peak data
for the region and its construction involved the averaging
out of the variations in the individual flood records.
5.3.3 Estimation of 01
(i) N

Year
1958
1959
1960
l96r
t962
1963
t9&
r 965
1966
1967
1968
Pe¡k (m¡ls)
2238
562
1506
702
1552
1644
2201
2859
2689
I 802
1082
Year
t969
t970
t91l
1972
1913
1974
1975
t976
1977
1978
Peak (m3ls)
6t3
2387
20t9
t9u
t094
1357
1690
l3l I
865
2875
The following four examples estimate the 100_year flood
peak Q,oo and the corresponding 68,3g0 confidence limits
lor the site, assuming that:
(¡) no flood record is available;
(ii) only the first 3 years of record, from l95g to 1960, are
available;
(¡iD l¿ years of record from 1958 to l97l are available;
(iv) the full length of record from I 95g to I 97g is available.
5.4.1 Example 1: N:e
e estimated from the regional
Figure 4. 10, the catchment lies
ellEast Cape flood region and
a = 2. 18 x l0-? AREA o ó1 MARAIN ,3!
Substituting the values for AREA and MARAIN as given
above produces:
a = 2.18 x l0-? X 13930 64 X 2550, 13
= l94O m'/s
(b) The regional curve ordinate should now be obtained.
The site is in the North Island East Coast flood frequency
region, i.e, Region 3 in Figure 3.6, and hence, lrom Table
3.4, the regional curve ordinate is:
Q'oo/Q = 2.89
. Alte^rnatively, Q,oolQ can be computed from the equa_
tion of the regional curve in Table 3.4:
Q/Q = 0.762+0.469y
For T = 100, y given by Equation 3.16 is
y : -ln(-ln(l- I ) )
= 4.60
100
(This result could also have been obtained irom Table 3.1.)
Substituting for y in the regional curve equation gives
Q'oo/Q : 0.726 + 0.469 x 4.60
: 2.88
(The difference of 0.01 is due to rounding effecrs.)
(c) Combining the estimates for Q and e,oole produces
Q'oo.
Thus Q,oo = 1944. x 2.89
= 5607 m3,/s
(d) The corresponding standard error of estimate is ob_
tained from Equation 3.25, namely
var(Qr) = E(Q),. var(ea/Q) + E(er/Q),. var(e)
The RHS terms of this equation are estimated as follows:
E(Q)
-- l9¿lo
From Equation 3.26
var (Q1/Q) : (Cr .
Qt )'
o
where, from Table 3.9
CF
(_t.zs + 5.74 tnT)/100
= 0.25
Thus var (Qr/Q) = @.25 x 2.89), = 0.522
Also E(Q'/Q) = 2.89
]tr9.ti1a!
term var (Q) is obtained from rhe p estimates in
Table 4.12. lf p is assumed to be 0.5, Cp : b.¡Of for the
Northland,/Coromandel,/East Cape flood- region. Since, by
definition,
cË = uar (Q)/Q'
.'. var(Q)= C'..Q,
: (0.301 x t940)'
= 3.410 x l0'
Reverting to Equation 3.25
var (Q'oo) = 1940'z x 0.522 + 2.89, x 3.410 x 105
= 4.813 x 10.
Therefore the standard error of estimate of e,oo is
Se (Q'oo) = (4.813 * 1gc¡t/z
= 2194 m,/s, which is 39Vo of e,on
Figure 5.2 Location of the Motu catchment above Houpoto.
1435 ml/s
Water & soil technical publication no. 20 (1982)
80
5.4.2 Exampte 2: N:3
(l) W¡th N = 3 = Nu, Q should be estimated from both
the flood record and the regional equation. Using the flood
record:
Qobs %Q238 + 562 + 1506)

Using the regional equation
Qest
1940 m'ls, as in Example I
Combining these estimates from the record and regional
equation, using a weighting factor of 0.5 for both (see section
5.2.2), gives
a = 0.5x1435+0.5x194O
1688 m',/s
(b) As N< 10, the regional curve should still be applied to
estimate Q,oo. The curve ordinate is unchanged at
Q,oolQ : 2.89
(c) Combining the estimates of Q and Q,oolQ results in
Q,oo 1688 x 2.89
= 4878 m!/s
(d) In obtaining the standard error of estimate, the RHS
terms in Equation 3.25 changed from Example I are
E(Q) = 1688 m3,/s
and the variance of Q estimated from the flood record is
given by
E(Q)
and
var(Q)
1704 m'ls
(cu.Q)'
N
= (0.54 x 1704)' = 6.048 x 10.
t4
Therefore, from Equation 3.25
var(Qroo) l1M' x 0.522 + 2.89' x 6.048 x l0'
= 2.021 x 106
Thus
Se(Q'oo) : (2.021 x106)v,
1422 m3/s which is 2590 of Q,oo
5.4.4 Example 4: N:21
(a) As in Example 3, Q can be estimated directly from the
annual series.
var(Qo6) - (Cn'Qou')'
2t
N
i]r
where C" :
The Cn for the 0.54 from
2l years of record is 0.43, which compares
Figure 4.12
well with the regional estimate of C" : 9.54
Thus
var(Qo6) : (0.54 x
(b) Since T ) 5N and N > 20, frequency analyses may be
1435)' : 2.002 x l0'
performed on the annual series using two- and three-parameter
distributions. The EVI distribution fitted by the
3
The variance
maximum
of
likelihood method gives
Q estimated from
a good fit to the data
the regional equation is
the
and yields
same as in Example l, i.e.,
var(QesJ = 3.410x105
Q'oo
: 4l7O m'/s
and an approximate standard error of estimate of 800 m',/s.
From Equation 4.10, the variance of the combined estimate (This
of Q is
standard error is based on a formula used by NERC
(1975, p. 170), assuming Cu : 0.54).
l:l+l
(c) The corresponding estimate using the regional curve is
var(Q) var(Qo') var(Q.r¡) 2.002 x l0r Q,oo 1665x2.89:4812m3/s
and the associated standard error of estimate is obtained
+
from Equation 3.25 as
3.410 x l0r
var(Q,oo) 1665' x 0.522 + 2.8g'z x
(0'54 x 1665)'z
so that var(Q) = 1.261 x 105
2l
Hence from Equation
1.769 x loó
3.25
so that
var(Qroo) 1688' 0.522 + 2.89'? x 1.261 x 105
: 2.541 x Se(Q'oo) 1330 m3,/s which is 2490 of
106
Q,oo
and
Se(Q,oo) = (2.541 x l0ó)/z
1594 m!/s, which is 2890 of Q,oo
5.4.5 Results Summary
Table 5.2 summarises the estimates of Q and Q'oo obtained
in the four examples using the RFE method.
5.4.3 Example 3: N: 14
The reduction in the standard error of estimate in Table
(a) As N > N"( = 3), Q can be estimated directly from the 5.2 with increase in record length illustrates the value of increasing
lengths of flood record. In Example 4, a second
annual series.
Hence
estimate of Q,oo : 4l7O m'ls (by frequency analysis of the
l4
2l years ofrecord) is available and a designer would choose
a = I a weighted mean of the two.
I ei =1704m',/s
It will be seen that the estimate of Q in the second example,
obtained by combining the estimates from the re-
14 i-: I
gional equation and the three years of record, is closer to
(b) Applying the regional curve produces
the Q estimate using the full flood record than that in Example
3 which is based on 14 years and, as a consequence,
Q'oo :1704 x2.89
= 4925 m3/s
the corresponding Q,oo estimate is also closer to the Qroo
estimate determined from the full record. Although this
may be a chance result it does emphasise that even a short
(c) The new RHS terms in Equation 3.25 are
flood record is useful.
Water & soil technical publication no. 20 (1982)
81
a
2t
= I )- Qi:1665m'/s

The estimate of Q from the regional equations is as
accurate as an estimate from about three y€ars of record
(Table 4. l2). If the typical variability is checked by drawing
samples from the Motu data listed earlier, or by considering
the standard error of the regional equation, it will be seen
that this particular estimate from the regional equation is
fortuitously close to the estimate from 2l years of record.
Table 5.2 Summary of selected results from the RFE method.
Example
number
1
2
3
4
Length of
recor.d
(yrsl
o
3
14
21
Estimate
ofO
(m3/s)
39
28
25
24
82
Water & soil technical publication no. 20 (1982)

6 Summary
In New Zealand little progress has been made in flood
estimation techniques over the last 25 years despite an upsurge
in the amount of streamflow data that has been col-
Iected over this period. This study has attempted to improve
this situation by
al flood frequency
analysis procedu
the available
annual and historical flo
I catchments'
The procedure, known as the Regional Flood Estimation
(RFË) method, is applicable to both gauged and ungauged
iural catchments which in general are greater than 20 km'
in area. Since the method was developed by averaging the
sampling variation that exists in individual flood records, it
should provide a more reliable design flood peak estimate
than that determined by fitting a frequency curve to a relatively
short record.
The RFE method comprises a set of eight regional flood
frequency cu
vs T, and a set of
niné regionat
when there is little
or no flood ¡
S the T-Year flood,
and Q is the mean annual flood. The most important independent
variables in the equations are catchment area
and an index of the catchment rainfall.
The regional curves may be used up to the 200-year return
period to estimate a design flood peak, except in the
Otago-Southland region where the upper limit on return
period is restricted to 100 years because of the limited data
in this area that were available for analysis. The curves are
defined by the straight-line extreme value type I (EVl) distribution
for all but two of the regions the Bay of Plenty
-
and South Canterbury regions, where the extreme value
type 2 (EV2) tlistribution was found to give a better definitión
of the regional trend in the data. Although the general
extreme value (C
gional curves, th
of the log-Pears
tion tests carried
that the LP3 distribution may well have given an equally
good description of the curves.
It is evident, both from the regional mass probability
plots and from the standard error equations derived for the
iegional curves, that the variability in the regional Qr/Q
data is well within acceptable limits. A quantitative indication
of the confidence that may be placed on values of
Q1/Q estimated fiom a regional curve is obtainable from
the standard error equations which give estimates comparing
very favourably with those given by the equivalent
NERC (1975) equation.
A feature of this study is the dependence of the results on
climate. This is illustrated by the regions, which are partially
consistent with recognised climatic boundaries, and
by the difference in slope of the western and eastern regional
curves. The latter curves have greater slopes, which
ãre uttributable to the greater variability in the flood peak
data for the eastern regions where the climate is drier and
the antecedent conditions more variable. Further indication
of the climatic influence is given by the regional equations
for estimating Q . ¡.lo physical characteristics, other than
catchment area, are included in the equations, the only
other important parameters being catchment rainfall estimates.
This suggests that climate may be the dominant factor
affecting flood peaks with magnitude equal to or
greater than the mean annual flood. Other factors often
considered important, such as geology and topography,
have been accounted for to some extent in the regionalisation
of the country.
The country is divided into two sets of regions' one set
for estimating Qr/Q and one for estimating Q. These are
very similar
t
tempts were
e
purposes, b
t
regions is a
a
Q1/Q and Q.
The application_of the method to a catchment for the
estimation of Q1/Q and
ted
in Chapter 5 with four
the
advantage, when only a
of
combining the estimates
uation
and the flood record to obtain a weighted average
"best" estimate of Q . t¡e precision of each equation is expressed
of record and,
àepend
estimate of Q
from a
he error of estimating
od record. Thus
when an important waterway project is being considered, a
recorder should be installed as soon as possible to record
the flood peaks.
In addition to the regional curves of Q1/Q which extend
up to a maximum of 200 years, generalised curves, one for
the west and one for the east, are given. These curves were
derived from all the flood peak data collected for this
study, excluding four extreme flood events, and they can be
applied from beyond the limit of the regional curves up to
the 1000-year return period. Of interest is the marked similarity
of these curves with those derived by Stevens and
ing too many regions. lt is envisaged that as more flood
p.ãk dut" become available, revisions and refinements will
te made to the RFE method' especially for the estimation
of Q.
In all cases, we recommend that other methods for estimating
design flood magnitude also should be used and the
results compared before a final figure is selected'
Water & soil technical publication no. 20 (1982)
83

Water & soil technical publication no. 20 (1982)

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In Australian Rainfatl and Runoff. Chapter 9. The
Institution of Engineers, Australia.
Jenkinson, A.F. 1955: The frequency distribution of the
annual maximum (or minimum) values of meteorological
elements. Quarterly Journal of Royal Meleorological
Society 87: 158-71.
Jowett, I.G.; Thompson, S.M. 1977: Clutha power development,
flows and design floods. Appendix 2 of
Environmental impact report on design and construction
proposals, Clutha Valley Developments,
Ministry of Vy'orks and Development, Wellington.
Leese, M.N. 1973: The use of censored data in estimated
T-year floods. Proceedings of the Madrid Symposium,
Design oÍ Water Resources Proiects with Inadequate
Data, Vol. 2. June 1973. UNESCO-WMO'
IASH. pp.563-75.
Linsley, R.K.; Kohler, M.A.; Paulhus, L.H. 1975: Hydrotogy
for Engineers. McGraw-Hill, New York.
McGuinness, J.L.; Brakensiek, D.L. 1964: Simplified techniques
for fitting frequency distributions to hydrologic
data. US Agriculturol Handbook No- 25. 42 p.
Maguiness, J.A.; Blackwood, P.l-.; Broome, P.; Beable'
M.E. (In prep a) A report on FRAN, a computer
program for the frequency analysis of extremes. Min-
Hydrology of flow control. Section 25-l In
Handbook of applied hvdrologv (Edited by V.T.
Chow). McGraw-Hill, New York'
Draper,
-1964:
N.R.; Smith, H. 1968: Applied regression analysis.
John WileY, New York. 407P.
istry of Works and Development, Wellington.
Water & soil technical publication no. 20 (1982)
85

Maguiness, J.A.; Blackwood, P.L.; Beable, M.E. (ln prep
b) A report on FRANCES, a computer program for
the frequency analysis of a censored sample. Ministry
of Works and Development, Wellington.
Matalas, N.C.; Gilroy, E.J. l9ó8: Some comments on regionalisation
in hydrologic studies. Journal of Water
Resources Research 4 (6): 136l-9.
Ministry of Works 1970: Re¡resentative Basins of New
Zealand. llater ond Soil Division, Miscellaneous
Hydrological Publication No. Z. Minisrry of Works,
Wellington.
Ministry of Works and Development 1979: Code of practice
for the design of bridge waterways. Ministry oÍ
Works and Development, Civil Division publication
CDP 705/C (Prepared by Water and Soil Division).
72 p.
National Water and Soil Conservation Organisation 1975:
Metric version of technical memorandum No. 61.
Ministry of Works and Development, Wellington.
Index to hydrological recording stations in
New Zealand 198O. lVater & Soil Mßcellaneous
Publication No. 18. Ministry of Works and Development,
Wellington.
-¡9El:
NERC 1975: Flood Studies Report, Vol. l. Natural Environment
Research Council, London.
Neill, C.R. 1973: Guide to Bridge Hydraulics. published
for Roads and Transportation Association of
Canada by University of Toronto press.
Newson, M. 1975: Mapwork for flood studies, part I : Selection
and derivation of indices. Report No. 25, Institute
oÍ Hydrology, Wallingford.
Pilgrim, D.H. 1966: Storm loss rates for regions with limited
data. Proceedings of the American Society of
Civil Engineers 92 (Hy 2): 193-2-06.
Pilgrim, D.H.; Cordery, l. 1974: Design flood estimation
- an appraisal of philosophies and needs. Reporl
No. 140, Vl/ater Research Laboratory, University of
New South Wales.
Robertson, N.G. 1963: The frequency of high intensity
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Rosenbrock, H.H. l9ó0: An automatic method of finding
the greatest or least value of a function. The Computer
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Sangal, B.P.; Kallio, R.W. 1977: Magnitude and frequency
of floods in Southern Ontario. Technicol
Bulletin Series No. 99, Inland Waters Directorote,
Waler Planning and Management Branch, Fßheries
and Environment, Canadø.
Schaake, J.C.; Geyer, J.C.; Knapp, J.W. 1962: Experimental
examination of the rational method. Proceedings
of lhe American Society of Civil Engineers 93
(Hy 6): 353-70.
Schnackenberg, E.C. 1949: Extreme flood discharges. proceedings
of the NZ Institution of Engineers 35
376-427.
Soil Conservation and Rivers Control Council 1957:
Floods in New Zealand, 1920-53. SCRCC, Wellington.
Stevens, M.J.; Lynn, P.P. 1978: Regional growth curves.
Report No. 52, Institute of Hydrology, llaltingford.
Thomas, D.M.; Benson, M.A. 1970: Generalisation of
streamflow characteristics from drainage basin characteristics.
US Geological Survey lüater Supply
Paper No. 1975.
Toebes, C.1972l. The surface water resources of New Zealand.
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Toebes, C.; Palmer, B.R. I969: Hydrological regions of
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Wellington.
Water & soil technical publication no. 20 (1982)
86

Appendix A : Tests with frequency distributions
4.1 Introduction
The General Extreme Value (GEV) distribution is detailed
in Chapter 3. The Gamma distribution, another general
distribution from which several other specific distributions
derive, is outlined below. Then a computer program
(FRAN) is described. This program was developed to
enable an evaluation of different lrequency analysis methods
on New Zealand flood data. It was found that the extreme
value type I (EVl) distribution fitted by the Jenkinson
method generally fitted the data well, but that in many
cases the EVI distribution l'itted with Gumbel's method of
leasl squares also gave satisfactory results.
4.2 Gamma distribution
The three-parameter Camma distribution is the same as
the Pearson Type 3 distribution. It has the pdl
f(x) : I (x-xo¡r-le-(x-xo)/li .....A.1
0rr(r)
which is defined for x > xo,
where xo
ù_
l)-
I'(r):
a location parameter,
a scale parameter,
a shape parameter, and
the Gamma function, equal to ("y- 1)! for
positive integer values of -y.
lf "y : ¡, (x) describes an exponential distribution; and if
xo = 0, f(x) describes a two-parameter Gamma distribution.
Like the CEV distribution (section 3.1.3), Equation A.l
describes a tämily of distributions, with each member characterised
by the value of the shape parameter, in this case 7.
This parameter is inversely related to the skewness of the
variate, and as the skewness gets smaller, "y increases and
Equation A.l tends to the Normal distribution (NERC
1975). When the skew is zero the symmetrical, two-parameter
Normal distribution applies, with the pdf
f(x) : I s- /tl(x- pl/ol'
"F
where ¡,r : a location parameter, and
o : ascaleparameter.
A2
The parameters ¡,t and o are, in fact, the population mean
and standard deviation, respectively, of the variate x.
An analogous situation to that described above applies
tbr the three-parameter log-Gamma distribution. This distribution
is the same as the log-Pearson Type 3 (LP3) distribution
and has a pdf of the form
f(x) : I (l'nx- xo)?- I e-(r)nx-xo)/B ..... 4.3
x0zf(r)
which is defined for x > e"n.
Like Equation A. I, Equation 4.3 describes a family of
distributions, with each member being described by a particular
value of 'y. When the skewness of the variate is zero,
the two-parameter log-Normal distribution applies, with
the pdf
f(x) : I s-
xoF
/,1 (t'nx- p\/ øl'
A4
which is defined for x > 0. The parameters p and r are now
the population mean and standard deviation of the natural
logarithms of the variate x.
The df for Equations A.t to 4.4 must be calculated numerically.
A.3 Methods used
The GEV distribution described in section 3.1.3 and the
Camma distribution outlined in section 4.2 have up to
three parameters: a location, a scale and a shape parameter.
These parameters must be estimatcd in the fitting ol a distribution
to a data sample. The various techniques of parameter
estimation, together with the choice of the parent distribution
that may be used, give rise to the dilferent frequency
analysis methods that are available.
This study considered seven different frequency analysis
methods. They were chosen on the basis of being the most
common or the most useful, and they were incorporated in
a computer program FRAN (Maguiness ef a/. in prep. a).
(Another computer program FRANCES (section 3.1.7) was
developed for use where historical information was available
(Maguiness e! al. in prep.b).) The methods used in
FRAN were the lollowing:
(1) the three-parameter log-Camma or LP3 distribution
fitted by the method of moments;
(2', -
the three-parameter log-Gamma or LP3 distribution,
with an adjusted coefficient ol skew fitted by the
method of moments'
-
(3) log-Normal distribution -
fitted by the maximum
likelihood method;
(4) GEV distribution -
fitted by the maximum likelihood
method;
Water & soil technical publication no. 20 (1982)
(5) EVI distribution fitted by the maximum likelihood
-
method;
(ó) EVI distribution -
fitted by the least squares method;
(7) EVI distribution -
using the Jenkinson (1969)
method.
Each of the methods is briefly described below with reference
to an annual series. In the case of methods I and 2,
the distribution involved is subsequently referred to as the
LP3 distribution. For a detailed explanation of the seven
methods, refer to the report on FRAN by Maguiness e/ a/.
(in prep. a).
Method I This method was recommended by the United
States Water Resources Council (1967) to be uniformly
adopted in that country as the standard method for flood
frequency analysis. The method in effect applies the threeparameter
Gamma (Pearson) distribution (Equation A.l)
to the logarithms of the annual series. The resulting frequency
curve is a flexible one; it can plot concave upwards
or downwards on log-Normal probability paper. It also incorporates
the two-parameter log-Normal distribution,
which plots as a straight line on the same paper.
The fitting technique is the method of moments, which
involves the calculation of the mean, standard deviation
and the coefficient of skew of the logarithmically transformed
series. These statistics are then used in the following
equation to obtain the desired flood estimate.
log'oX1 : X +K.S
A5
where X1 : flood estimate for return period T,
X : mean of the transformed series,
S : standard deviation of the translormed
series, and
K : afrequencyfactor.
87

The liequency factor K is a function of the coefficient of
skew and the return period and may be obtained from
tables (e.g., Harter 1969; USWRC 1967). The form of
Equation 4.5, which is based on the use of a frequency factor,
is preferred to the more formal type of LP3 equation
(e.g., Equation A.3) for the method of moments fitting
technique, as it makes the computations very much easier.
The frequency factor idea has heen propounded by Foster
(1924) and Chow (1951), and the derivation of the factor
for the LP3 distribution is explained by NERC (1975, pp.
39-40) and Kite (1976, pp. 198-204,2291.
Method 2 This method is the same as Method l, except
that an adjustment is made to the computed skew coefficient.
An adjustment is warranted because the computed
skew value is likely to be unreliable for a data sample of
typical size. Indeed, it has been suggested (Beard and Frederick
1975) that at least 100 sample items are needed to obtain
a skew value that is representative of the population
statistic. Since most hydrological data samples are much
smaller than this, various efforts have been made to improve
the reliability of the computed skew value through
the use of generalised skew coeflficients (Beard 1977). One
example is the use of a regional skew value taken from isolines
of computed skew values.
ln the early stages of this New Zealand study, computed
skew values lbr flow stations in the top half of the South
Island were plotted on a map to determine if there was any
pattern in the skew coefficient. None was evident and,
hence, the possibility of using generalised skew coefficients
in this study was not pursued. Instead, the following tactor
Fu, recommended by Bobée and Robitaille (1975), was used
to adlust for the bias in the skew value that is due to the
length of the data sample.
Fo=
where CS = the computed skew coefficient, and
n : the number of sample items.
The adjustment is made by multiplying the computed
skew coefficient by Fu, but only when Equation 4.6 is
applicable i.e., for samples with 20 or more items.
Mefhod 3 This method is often referred to as the log-
Normal method and uses the two-parameter log-Normal
distribution, as distinct from the three-parameter one (see
Kite 1976). The method has long been advocated for use in
hydrological frequency analysis (e.g., Hazen l9t4), and appeals
because of its simplicity the fitted frequency distribution
plots -
as a straight line on log-Normal probability
paper.
The application of the method involves the same computations
as for Method l, except that the coefficient of skew
of the logarithms of the series is set to zero.
Method 4 This uses the maximum likelihood (ML)
method to fit the CEV distribution to a data sample. This
method of fitting is generally recognised as the most efficient
for estimating the distribution parameters, and its use is
recommended when the design events must be extracted
from a small or irregular series (WMO 1969). However, the
ML method involves equations that have no explicit solution.
The solution is complex and requires the use of an
iterative numerical scheme, and is only worthwhile attempting
with the aid of a computer.
Method 5 Although the GEV distribution incorporates
EVI as a special case, only rarely will the application of
Method 4 result in the EVI distribution being fitted to a
data sample. To ensure that a fit was obtained with the EVI
distribution, this distribution was fitted separately (by the
ML method) to the sample by setting the shape parameter k
in the CEV distribution to zero.
88
¡ 16-11- *ry i.i,*
.Tì"... ou
Method ó This method is often called the "Gumbel
method" after Gumbel (1941, 1954) and is probably the
one most commonly employed in hydrology. lt has had
wide use in New Zealand and was the method adopted by
the New Zealand Meteorological Service (Robertson l9ó3)
when determining rainfall depth-duration-f'requency relationships
from New Zealand data.
Melhod 7 This method follows the procedure devised by
Jenkinson (1955, 1969) and also described by Samuelsson
(1972). The method emphasises the extreme part of annual
series and as shown by Samuelsson, it can be applied as the
standard one to extreme values which belong to several different
kinds of frequency distribution. A larger series of
S-year maxima is produced from the annual series by considering
all possible combinations of items of five in the
original series. The EVI distribution is then fittcd to rhe
series of 5-year maxima by the ML method.
If an annual series is used in a lrequency analysis instead
of a series of 5-year maxima, it is quite possible that the
series may be non-homogeneous in that, for example, the
smaller items may belong to one distribution (e.g., EV2)
and the larger ones to another (e.g., EV3). Further, it can
be shown mathematically (WMO 1969) that the lower parr
(37V0) of the series may not even belong to the extreme
value distribution as it is defined. The advantage of the Jenkinson
method is that it generally overcornes this problem
of non-homogeneity of data. The use of 5-year maxima can
be thought of an increasing by fivefold the degree ol independence
in the data, so that these maxinra should then
form a homogeneous set of data that confbrms to EV
theory.
4.4 Evaluation of the frequency analys¡s
methods
4.4.1 General
Prior to the development of the regional curves, two
evaluation tests were carried out on 42 flood records altogether,
using the seven frequency analysis methods described
in section 4.3 and contained in the computer program
FRAN. The purpose of the tests was twofold:
(¡) to observe, and to indicate to users of FRAN, the relative
merits of the seven different methods on individual
New Zealand flood records;
(ii) to assist in the selection of a frequency distribution
that would adequately describe the regional curves.
This section describes the tests and discusses the results
obtained.
4.4.2 Evaluation criteria and method
Most studies that have attempted to discriminate between
frequency analysis methods have relied, at least to some extent,
on objective goodness-of-fit indices. Recent examples
of such studies are those carried out by Benson (1968),
Beard (1974), Kite (1976) NERC (t975), Kopiuke ef ø/.
(1976) and Bobée and Robitaille (1977). However, as is generally
acknowledged (e.g., Benson 1968), the classical
goodness-of-fit indices such as Chi-square and Kolmogorov-Smirnov
are not sufficiently sensitive or powerful
enough, because of the small samples found in hydrology,
to distinguish between the worth of different frequency analysis
methods. Moreover, NERC (1975) found that other
goodness-oi-fit indices had major weaknesses and concluded
that, because of the deficiencies ol goodness-of-fìt
indices, a visual inspection must be made of the probability
plots. The judgement on the performance of a method is
then a subjective one, "... but the objective tests that are
available are so ineffective that their objectivity alone is insufficient
to recommend them" (NERC 1975).
In the evaluation tests, much more emphasis was placed
on the probability plots than on the Chi-square value,
which the computer program calculated. F-ollowing an ex-
Water & soil technical publication no. 20 (1982)

amination of the probability plots for each station, the perlormance
of each frequency analysis method was classified
into a good, reasonable or poor category according to the
following four criteria:
(i) the frequency curve should fit the whole of the series
well, but particularly the upper half of the series;
(¡i) the frequency curve should not necessarily pass
through the very largest items in the series, since there
is a far larger sampling variation with these items;
(¡¡¡) the frequency curve should appear to produce a good
estimate of the 10O-year flood peak;
(iv) the Chi-square value should not be abnormally high.
Criterion (iii) needs some explanation. Although a
method could perform well under criterion (i), it could not
be automatically assumed that the method therefore gave a
sensible estimate oI the 10O-year flood peak. Because of the
small-sample effect with some of the samples used, a method
could produce an extremely good fit to a data sample
but a 100-year value that was only minimally greater (e.9.,
less than l-290) than the 2O-year value. One hundred years
was chosen as the return period for the flood peak estimate
on the basis of it being the most commonly used maximum
value in bridge waterway design (MWD 1979). It follows,
therefore, that the subsequent evaluations of the methods
for fitting individual station data are with reference to this
maximum return period and they should not be interpreted
as being applicable beyond the 100-year return period.
Afler the classification of the performances of the
methods they were then quantified, by allotting a score of 2
for each good fit, I lor each reasonable fit and 0 for each
poor fit.
A.4.3 F¡rst test
The first evaluation test was made midway through the
data collection phase when all the annual flood peak data
had been collected for the South Island stations. The results
of this test were presented and discussed by Maguiness et al.
(1977). Of the 50 stations for which data were available, 28
stations were selected for the test (see Table A. I for
details). These stations were considered to have reasonably
reliable streamflow records and each flood record was l0 or
more years in length. Altogether there were 377 station
years of rccord, giving an average length of 13.5 years per
station.
The performance of the different methods is summarised
in Table 4.2, which shows the number of times each
method gave a good, reasonable and poor performance. It
also shows the final score for each method after the performances
were quantified. The adjusted LP3 method is
not included in the table, since in only one case was the record
length long enough (20 years or greater) for an adjustment
to be made to the coefficient of skew using Equation
4.6.
As can be seen from Table 4.2 the Jenkinson method
performed best, scoring 52 out of a possible 56. lt produced
Table 4.1 Deta¡ls of the f low stations used in the first evaluation
test.
Site No.
56901
57502
60110
60114
621 03
621 05
64301
64602
64606
65104
65107
69302
69506
69614
6961 I
6962 1
71 103
71116
71129
7'l 135
93203
93204
93205
93206
93209
93211
93212
93217
Flow Station
Catchmenl Record
area, km' Length,
Years
Riwaka at Moss bush 48 10
Wairoa at Gorge 464 15
Waihopai at Craiglochart 744 16
Wairau at Dip Flat 505 25
Acheron at Clarence 997 18
Clarence at Jollies 44O
'l 3
Conway at Hundalee 47O 12
Waiau-uha at Marble Point 1980 14
Waiau-uha at Malings Pass 74-6 10
Hurunui at Mandamus 1 O7O 1 I
Hurunui at Lake Sumner 342 1 5
Rangitata above Klondyke 1495 10
Orari at Silverton 52O 15
Opuha at Skipton 456 12
Opihi at Rockwood 412 12
Rocky Gully at Rockburn 22.4 10
Hakataramea at M.H. Bridge 899 13
Ahuriri at South Diadem 557 12
Forks at Balmoral 13O
'l 1
Jollie at Mt Cook Station 1 39 10
Buller at Te Kuha 6350 14
Buller at Berlins 5960 16
Buller at Woolfs 4560 11
lnangahua at Land¡ng 1000
'l 3
Maruia at Falls 980 1 1
Matakitaki at Mud Lake 857 13
Mangles at Gorge 284 16
Glenroy at Blicks 198 1 1
377
what were considered good fits on 24 occasions (or more
than 8590 of the time) and, significantly, gave no poor fits.
Next in order of performance were the LP3 and the
Gumbel methods, scoring 4l and 39 respectively. The former
method gave only slightly more good fits than the latter,
and both produced only a minimal number of poor fits.
At the lower end of the performance rankings were the
EVl,log-Normal and GEV methods. Little distinction can
be made between the EVI and log-Normal methods, with
both giving on average about the same performance. In
comparison, the CEV method gave fewer poor fits, but at
the same time produced only three good lits -
less than
half the number achieved by each of the other two
methods.
The flood records used in this first test were relatively
small samples. Although each record was at least l0 years
long, this is the minimum acceptable length for a flood frequency
analysis. The average record length of 13.5 years is
only a marginal improvement on this and is still less than
the minimum length of l5-20 years recommended by some,
Table 4.2 Summary of the performance of the methods ¡n the f¡rst test.
Method
Performance
Categories
No. 1
LP3
No. 3
Log-Normal
No. 4
GEV
No. 5
EV1
No. 6
Gumbel
No. 7
Jenkinson
Good
Reasonable
Poor
Number Score Number Score Number Score Number Score Number Score Number Score
16 32
99
30
Total Score:
4'l
27 26
Note: Score calculated as 2 for good fit, 1 for resonable, O for poor fit.
Maximum possible score: 2 x 2a :56
8
'l 6 3 6 11 22 13 26 24 48
11 11 20 20 7 7 13 13 4 4
9 0 5 0 10 0 2 0 0 0
Water & soil technical publication no. 20 (1982)
89

e.9., Linsley et ol. (1915); lrish and Ashkanasy (1977).
There was, in fact, only one station with more than 20 years
of record. However, these relatively small samples reflect
the situation the design engineer is often faced with
- having
to estimate design figures from records of barely adequate
length.
Most of the findings of the test could only be regarded as
preliminary ones pending further investigation with larger
samples and covering a great'Jr part of the country. The
findings are a guide to the design engineer using a small
sample in flood frequency analysis, but the test itself was
not very helpful in the choosing of a distribution for the regional
curves. A second test was therefore carried out at the
end of the data collection phase using larger data samples.
4.4.4 Second test
The second evaluation test used annual series data from
14 stations with 20 or more years of record. Details of these
stations are listed in Table 4.3. As shown in the table, there
was a total of 366 station years of record, giving an average
record length of 26.1 years per station, almost double the
figure for the first test.
The performances of the different methods on the second
set of data were evaluated in exactly the same manner
as tbr the first test. The results of the evaluation are summarised
in Table A.4.
Table A.4 shows that the Jenkinson method again performed
best, but this time the Cumbel method gave a pertbrmance
that was almost as good. Notably, neither
method gave any poor fits to the data. At the second level
of performance were the GEV and LP3 (unadjusted and
adjusted) methods, all with the same score of 22. The performances
of the unadjusted and adjusted LP3 methods
were indistinguishable and the two methods are collectively
referred to as the LP3 method. Last were the log-Normal
and EVI methods. Both methods gave good fits at least
5090 of the time, but also a noticeable percentage (2190) of
poor fits.
As in the lirst test, the Jenkinson method performed the
best ot'the methods, and in this second test could rarely be
faulted. ln the one instance where it gave other than a good
performance, its frequency curve still fitted the data well
and produced a realistic 100-year flood peak estimate.
However, its performance was reduced because of its Chisquare
value, which was high and more than twice that for
any of the other methods. Some allowance was always
made for a higher Chi-si¡uare value with the Jenkinson
method, but in this particular case the value was excessively
high. The higher values for the method are caused by the
fact that the frequency curve does not always fit the lowest
four items in a series, since these items clo not form part of
the generated 5-year maxima to which the method fits the
EVI curve.
The Cumbel method improved on its first test ranking
giving an overall performance almost the same as the Jenkinson
method. However, a surprising aspect in both tests
Tabþ 4.3 Details of the flow stations used in the second evaluation
test.
Site No.
Flow Station
Catchment Record
area, km' Length,
yeafs
14614 Kaituna at Te Matai 958 21
1551 1 Waimana at Waimana Gorge 44O 25
1 5514 Whakatane at Whakatane 1 557 20
29201 Ruamahanga at Wardells 637 22
29202 Ruamahanga at Waihenga 2340 21
29224 Waiohine at Gorge 183 22
32502 Manawatu at Fitzherbert 3916 48
32503 Manawatu at Weber Road 713 22
32514 Oroua at Almadale 312 24
32526 Mangahao at Ballance 266 24
32529 Tiraumea at Ngaturi 734 24
601 14 Wairau at Dip Flat 5O5 25
92216 Buller at Lake Rotoiti 195 26
93213 Gowan at Lake Rotoroa 368 42
366
was the difference in performance between the Gumbel and
EVI methods. Both fit the same distribution (EVl) to a
series yet the EVI method did not perform as well, presumably
because the ML fitting technique, in comparison with
the least-squares technique, puts relatively greater weight
on the smaller items in a data series (Gumbel 1966). Consequently,
if the upper half of a series exhibited a different
trend. to that for the lower half, the EVI method, especially,
did not always produce a good fit to the upper half
and its performance suffered accordingly. In addition, the
visual inspection of the goodness-of-fit of the frequency
curves may have given the Gumbel method an unfair advantage
over the EVI method, since curve-fitting by eye can
be considered as a least-squares fit (Chernoff and Lieberman
1954, 1956). Thus, although the results may indicate
that the Gumbel method may be a worthy substitute for the
Jenkinson method when a computer is unavailable, the
evaluation may have been weighted unfairly in favour of
the Gumbel method.
The methods using three-parameter distributions, i.e.,
the LP3 and the GEV methods, displayed their greater flexibility
over the two-parameter methods by always producing
a curve that fitted the data particularly well. However,
occasionally this was to their detriment, because the
resulting 100-year flood peak estimate was sometimes not
very realistic. For example, in the case where the LP3
method gave a poor performance, the curve fitted the data
very well; so well in fact that it was almost horizontal at the
high return periods. The difference between the 20 and
10O-year flood peaks estimated from the curve was less than
0.690, indicating an implausible 10O-year flood peak estimate.
Table A.4 Summary of the performance of the methods in the second test.
Method
Performance
Categories
No. 1
LP3
No. 2
Adjusted
LP3
No. 3
Log-Normal
No. 4
GEV
No.5
EV1
No. 6
Gumbel
No. 7
Jenkinson
No Score No. Score No, Score No. Score No. Score No. Score No. Score
Good
Reasonable
Poor
9 18 I 18 9 18 8 16 7 ',t4 12 24 13 26
44442266442211
10103000300000
Total Score
22
22 20 ?2 18 26
27
Note: Maximum possible score = 28
Water & soil technical publication no. 20 (1982)
90

In the first test the GEV method was often affected in
this manner, producing many curves that fitted the data
very well but giving 100-year flood peak estimates that were
not always sensible. For example, the trend in the lower
half of the series would cause the GEV curve to flatten off
at the top end, impþing that there was a limit to flood
peaks of about twice the mean annual flood. While there
may be an upper limit to flood magnitude, it is certainly
more than the figure implied (see Tables 3.3 and 3.6).
In comparison, the straight-line fits of the Gumbel and
EVI methods were often a good approximation to the data
and gave more sensible 100-year flood peak estimates.
However, this better performance by the t$'o-pa¡ameter
methods can be attributed to the small samples used
(NERC 1975; pp. 159-60). The fact that the Gumbel
method still performed better than the GEV method in the
second test suggests that the samples in this test may also
have been small. However, it is also likely that the leastsquÍues
fitting technique of the Gumbel method influenced
the evaluation test in the method's favour.
The two-parameter log-Normal method also gave good
approximations to the data at times, producing a reasonable
proportion of good fits. However, the method assumes
that there is no skew in the logarithms of the series, an
assumption which was rarely true. Hence the method did
not perform as well as others in the test, including its parent
method, the three-parameter LP3.
A.4.5 Gonclusions
The evaluations in the two tests involved a good deal of
subjective judgement, but this typifies the present situation,
with the objective goodness-of-fit indices not providing rigorous
enough criteria for discriminating between different
frequency analysis methods.
From the findings of the tests, the following conclusions
were reached:
(¡) the Jenkinson method was the superior method in both
tests and should be used in flood frequency analysis,
especially when the sample is small;
(iÐ the Gumbel method improved in performance with increase
in sample size, and should be a satisfactory alternative
to the Jenkinson method on the larger sam-
Ples;
(ii¡) the GEV and LP3 methods were more flexible than the
two-parameter methods, with their frequency curves
geneially following the trend in the data extremeiy
well;
(iv) on small samples, in particular, the straight-line fits
from the two-parameter methods can give good approximations
to the data and sometimes more sensible
results than those obtained from their parent threeparameter
methods;
(v) on small samples the LP3 method appears to perform
better than the GEV method, being influenced less by
the trend in the lower part of a series;
(vi) on larger samples the GEV and LP3 methods can produce
similar shaped curves and give a comparable performance.
These conclusions apply for individual records and up to
References
Beard, L.R. 1974: Flood flow frequency techniques. Center
tor Research in Water Rnources, Univercity of
Texas, Austin, Technicøl Report CRVR-|19.
1977: Guidelines for determining flood flow frequency.
U.S. Water Resounaes Council, Bulletin No.
I7A of the Hydrologlt Committee.
Beard, L.R.; Frederick, A.J. 1975: Hydrologic frequency
analysis. .In Hydrologic Engineering Methods for
Water Resources Development Vol. 3. The Hydrologic
Engineering Center, U.S. Army Corps of Engineers,
Davis, California.
Benson, M.A. 1968: Uniform flood-frequency estimating
methods for federal agencies. Water Resources Reæørch
4(5):891-908.
Bobée, B.B. Robitaille, R. 195: Correction of bias in the
estimation of the co-efficient of skewness. Wøter Resources
Research I I (6): 841-4.
1977: The use of the Pea¡son type 3 and Log-
Pearson type 3 distributions revisited. lfoter Resoutces
Research I 3(2): 427 -41.
Chernoff, H.; Lieberman, G.J. 1954: Use of normal probability
paper. Journøl of the Americøn Stotisticol
Associotion 49: 778-85.
1956: The use ofgeneralised probability paper for
continuous distributions. Annals of Mathemoticol
Statistics 27:806-18.
Chow. V.T. l95l: A general formula for hydrologic frequency
analysis. Tronsactions of the Americøn Geophysicol
Union 32(2): 231-7.
Foster, H.A. l9A: Theoretical frequency curves and their
applications to engineering. Tronsactiotts of the
American Society ol Civil Engineen 872 142-73.
Gumbel, E.J. l94l: The return period of flood flows. ánnols
of Mathemotical Stotistics 12: 163-X).
1954: Statistical theory of extreme values and
some practical applications. US Bureou of Slondards,
Applied Mathemotics Series 33l. 15-16.
l!Xó: Extreme value analysis of hydrologic data.
In Statistical Methods of Hydrology. Proceedings of
Hydrology Symposium No. 5, McGill University,
Canada, Z,-25Februw. pp. 147-69.
Harter, H.L. 1969: A new table of percentage points of the
Pearson Type III distribution. Technometrics Il(l):
177-81.
Hazen, A. l9l4: Storage to be provided in impounding reservoirs
for municipal water supply. Transøctions of
the American Society of Civil Engineers 78:
1539-641.
Irish, J.; Ashkanasy, N.M. 1977: Flood frequency analysis.
I¿ Australian Rainfall and Runoff. Chapter 9' The
Institution of Engineers, Australia.
Jenkinson, A.F. 1955: The frequency distribution of the
annual maximum (or minimum) values of meteoro-.
logical elements. Quorterly Journal of Royal Meteo'
rological Society 87: 158-71.
Statistics of extremes. Iz Estimation of
Maximum Floods. Chapter 5. VMO Technicql Nole
No.98. pp.193-227.
-1969:
Kite, G.W. 1976: Frequency and risk analyses in hydrology.
Inland Waters Directorate, Water Resources Branch,
Dept. of E
Kopittke, R.A.;
e, K.S. 1976: Fre"
quency an
in Queensland. Ia
tion of Enginæn,
Hydrology
Austroliq, Notionsl Co4ference Publication' No.
76/2. pp.2È4.
Linsley, R.K.; Kohler, M.A.; Paulhus, L.H. 195: Hydrology
for Engineers. McGraw-Hill, New York.
Water & soil technical publication no. 20 (1982)
9l

Maguiness, J.A.; Blackwood, P.L.; Broome, P.; Beable,
M.E. (In prep. a): A report on FRAN, a computer
program for the frequency analysis ofextrernes. Ministry
of lVorks and Development, lVellin$on.
Maguiness, J.A.; Blackwood, P.L.; Beable, M.E. (In prep.
b): A report on FRANCES, a computer program for
the frequency analysis of a censored sample. Ministry
of Works and Development, Wellington.
Maguiness, J.A.; McBride, G.B.; Beable, M.E. 1977:
FRAN a computer program for the frequency analysis
of extremes. Presented at the New Zealand Hy-
-
drological Society Annual Symposium, Christchurch,
November. l6p.
Ministry of Works and Development 1979: Code of practice
for the design of bridge waterways. Ministry o!
Works and Development, Civil Dìvision publìcatíon
CDP 705/C (Prepared by lVater and Soil Division).
72p.
NERC 195: Flood Studies Rcport Vol. l, Hydrological
Studics. Natural Environmental Resea¡ch Council,
London.
Robertson, N.G. 1963: The frequency of high intensity
rainfalls in New Zqland. New Z¿stand Meteorologicol
Semiæ, Misællaneous publicotion II8.
Samuelsson, B. lï12: Statistical interpretation of hydrometeorological
extreme values. Nordic Hydrologlt
3(4): 19D'-213.
US\VRC 1967: A uniform technique for determining flood
flow frequencies. Hydrologt Committee, US llater
Resources Councí|, Eulletin JVa 15. 15 p.
IVMO l%9: Estimation of Ma¡rimum Floods. llorld Meteorologicol
Organisøtion Tæhnicøl Note No. 98.
92
Water & soil technical publication no. 20 (1982)

APPENDIX B
Summary of Flood Peak Data used in the
Regional Flood Frequency Analysis.
CONTENTS
Northern North Island Data
North Island West Coast Data
Manawatu-Rangitikei Data
Southern North Island Data
Bay of Plenty Data
North Island East Coast Data
Central Hawke's Bay Data
South Island West Coast Data
South Island East Coast Data
South Canteibury Data
Otago-Southland Data
Prge
93
94
96
97
98
I
100
l0l
103
104
105
NOTE: The rules mentioned for some stations concerning
the rejection of data refer to those given in Section
3.2.2.
1A. NORTHERN NORTH ISI.AND DATA
srtr 350 6
ClrCÍilll rRE^. s0 t(É =
¡trlEEl o? rf,[urL PEtÍs =
tllB PEr( tElR
1958 q7. S 195c
1912 r¡C.9 l97l
1976 5q.6 197?
iElI =
PEIK
38.9
56. C
36. 6
57. B sTD. Dtlv. =
ntuNGAprRERÍrÀ R IT TynFzs Fonn
11. 1 ilÀP REFEFtT¡CE
1T PEAIOD OP PNC.
YEIR PFTK
1970 69.3
88 . c
19"r¡
YEÀR
1971
197s
¡t l: 39 1555
1968-77
PE¡ K
69. 6
?0. 1
17.0 coFF. oF sXE¡ = C.3?66
S IlE 9101 rÀITOI P TT IISTI(¡HOFO DRIDGF
CtrcElElll lEEt, SQ Kll = 433 llÀP BßPEFDfct = tl53:082804
fUlEE¡ 0P t[Xnrl PEtrS = 17 PEATOD OP PrC. = 1952-6Ê
ts¡R PEÀK TEÀR PEÀK IEAR PBTI( tEÀR PEIX
1952 25.1 t9S3 t¡6.C, rc 5¡ 68.0 1955 20.6
I 956 q1.7 1957 38.5 1958 26.2 t959 22.Ã
I 960 58.0 1961 9q. i '1962 05.0 1C53 10.n
t 96tt 29.5 196s 52,6 1966 11.5 1961 47" 0
1 969 qB.2
IEli =
q3.6 srD. DEV. = 19.5 CoEF. oF SKU¡ = 1.4380
IOTES:
1. îßE 1961 PLOOD Ptf,t( ÍÀS ÎÀKElt THE I.ÀPGEST rI THP
Pfnron 1908-7?-
^S
SITE 9118
Prtio ! À1 38tfl80lo tolD
CÀlcHllPlll ÀREl' s0 l(lt = 528 llP FEIEREtIcE r57:005700
l{UllBER oP riÍûtL PEt(S = 17 PERIOD 0F REc. = 1953-69
YEIR PEÀI fE¡R PBT¡ tEÀ8 PEÀf, YUIN PI¡f
1953 r 1 3.8 195¡t 12,7 1955 35.5 1956 100.9
1957 l¡c,8 19t9 1 33.5 1959 38.1 1960 265.0
1961 295.6 1962 I 28.3 1963 19.6 196¡ 71.2
1965 8f,2 1966 143.2 '1961 2 13.5 1968 10f.0
1969 15,2
IiEt[ = 120,0 STD. DEV. 16.7 cogl. o! sß¿9 = 1. l9l5
¡otEs:
1. THE 1C6I PLOOD PEÀK ¡ÀS ÎÀf,EN ÀS ÎR' LIRGEST ¡' 1¡I
PFnton 1908-77.
SITE 9203
ctTcññEIÎ t8P^, SQ Kll = 1606 ËrP REFEBE¡cr = 153: ll¡9tz
lgIBER oP ¡ùr0ÀL PEÀKs = 1a PTRIoD 0P REc. ¡ 195È76
IETR PTÀi YEÀF PETK YF¡R PBIR rEr¡ Ptlr
t 958 611 1959 652 1960 920 196t 330
1962 637 1 96 I 32C 1964 184 1965 397
1 966 595 1967 283 t968 tr87 1969 290
1 970 260 191 1 397 1912 3¡8 1973 2a1
1974 291 1913 330 1976 736
ñt:Àl¡ = 450 sTD. DEV. =
:1113:-:-!1-::ï-::i::
2C0 COEP. OF SXtl - 0.7068
tolEs:
1. TffE'1960 PLOOD P?Àr ¡àS TrKEll 15 lEE L¡RGn5î rl lEl
PERTOD 1929-76.
sI?t
38 19
TTIHÄRIKEXP R ÀT |ILIOI BIIIi
5II E
OIIIf,ÈIORT R 11 CRITEIIOT II
cÀTcRlE[T rBEr, SQ K11 =
IUÉBER oP tflN0ÀL PElKs =
IEIS PF.AK IPÀ R PEÀK
t968 201.0 1969 6?.5
1912 115. 1 l97l ?4.0
1916 97. 0 .t911 81. 0
tEtr = 1c7,3 sîD. DEV, =
srTE
q901
IBT¡ PETÍ IBTE PE¡Í
1910 31 . 6 1971 69, rl
1 9tr 62.6 1975 121 .5
lBll = 83.9 sTD. DEv. =
srts 5S09
229
1a
llAP REPERtI¡cE = ll1:,:52936]
PliRIoD oP FFc. = 1968-77
YEIR SEÀK YEIR PEÀ¡
1970 54, s 1971 163.5
197tt 1t!2.5 1915 11 . O
47.7 COEP. OP sÍE¡ = 0.9620
IIGUIIGORTI 8 TT DÛGIIORES ROCX
cÀrcñ;Exr ÀREr, s0 I(ll = 12.5 rAP REFBREIICE = r20:9q2120
IftãBER OP tr¡0ÀL pElÍS = I PESIoD oF FEc. = 1910-11
IEÀR PETK ÍETN PEIK
'1972 4a.1 1913 I 13.0
1916 I 31 . 1 1911 94. 6
36.5 coEP. oP sKE¡l E -0.0788
Tï:ï1_:_1I_ l::::11-l9ll
CttCEüELl tBEt, S0 [i = 16.2 llÀP REPEREIICP
v20.a279a2
f0rBr8 oF lrlotl PEÀÍS = 10 PERIoD 0F FEC. = 1958-6"
IITE PTIÍ I?IR PEÀ¡ rltR PEtx YE¡N PEÀX
1958 73.3 1959 4C.2 1960 113.9 19n l 66.5
1962 63,1 t96l 23.6 1964 16.8 1965 14,6
1966 146.7 1961 87.5
iE¡i = 64.6 ST¡. DEl. = tr3'3 COEP. oP SrEr = 0.6302
TOT'S:
1. lEE t956 ¡LOOD PEltr OP 210 cÛllEcs
LI¡GEST Ir TEE P9RroD 1850-1967.
sITt 8501
rts Tl(E[ rs TflE
TIIROÀ R À1 ¡EIR
CtTCriEIl tREt, sO lá 12.6? rlP REPEFPTICB X4€:631301
roqrtn oF r¡roir, p¡rrs = 15 PERToD oP REc' = 1960-74
T!À¡ PEIi TETR PET( YETR P8¡K II'TR PE¡X
iioo 37.q 1961 3o.s 1962 33.2 1963 21,1
ti¡c 33.8 1965 26.r ß66 5?. I 196? 15.4
1968 19.5 1969 11.9 1970 J2-'t 1"11 9' 6
1972 1 3. 6 1,9ai 22-5 1914 36.6
iBtI = 31.2 sfD. DEl. = 17.0 COEP. oF SKEI - l'l'382
ctT:ñtEl¡T tBE[, sQ Kll =
ll0liBEF 0P t[¡Uf,L PEtXs =
IEIR PSTK
195rr 619
1959 656
1963 300
1968 538
lEÀI = 112
308
1l
ütP BB?EREÍcs = I53: ttt95t
PERIoD 0! 8Ec. - t95l-68
fEtt PElf rt¡t Pllr
r 9 5? ?.55 1950 515
l96t c56 1962 501
1966 592 1967 33¡
taoTEs:
1. lEE 1036 FLOOD FElr, ESlrllllED T0 BE e9? CUiECS, l¡5
lIKEII ÀS TF¡ LTRGEST III TIII PESIOD 18?5-196E.
2. [O DrTr CÀS tVArttALE P5R 1955 lltl 1951'
sfrE 9211
IETN PPTK
'1951 218
1961 112
1965 120
196 9 rrTd
197 3 ?o5
IBÀf, =
r¡l5
fEI R PEIÍ
1956 53F
1 96 ! 52tt
1965 31q
STD. DEY. =
cÀÎctillEflT ÀREr, S0 Kll
rauü8ER oF rù[[ÀL PEtKS
YEIR
195I
1962
19 66
1 I'C
= :87
PTIIK
q63
50c
67C
184
STD. ftnv. = 1? 1
loTEs:
1. îfiF 1916 FLOoD PEAK OP 9r¡C C0ñECS
LtFGESî rÙ lHE FERTOD 1875-1977.
srlE 9221
crlcElllfl rall, s0 rl =
¡olBlR oF lliûlL Pltf,S =
Water & soil technical publication no. 20 (1982)
IEIB PETtr IEI R PETi
196q 10 1965 130
1968 124 1969 12C
1972 14¡ 19711 142
trlt . t53 sro. oÉs. =
98q
12
130 CO!F. OP sßll = -0.1680
oHrrPinF¡ n lr f,t¡llGlllil
itP Rf,PgFrtacE = Ã5322OA922
PFFIoD ol RqC. = 1951-73
YEIR PEÂT IEIS
1959 61¡ i960
1 96f 2c0 t 961
1967 336 1968
rq? r 6'11 1912
coEr. oF srE¡ = -0.0389
cls TlÍEx ts TnE
PtlI
¡50 g0
650
357
cttEou R rT s8ÀPlFsBt¡Rt
lÀP RErBnlXc¡ I57:263663
PERIOD OP REc. = 1960-76
TEÀR PE¡X TEÀR PETf,
1966 l?C t967 200
1970 16C 1971 155
1975 135 t976 200
28 COE!. oP sl(P¡ = 0.7875
tolBs:
t. î[t t960 PLOOD PEIK 0l 250 C0llECS l¡S TIXEN rS T¡rE
LIBGESÎ Il llB PESTOD 1960-1976.
2. to t¡¡otL PEtÍ 9¡S ItlrLÀBLE FOR 1973,
93

sltt 930 t [rûltRÀict ¡ l? s;¡tts S IlE q66 25 IIfr¡rltcI ¡ ¡1 rrro-Írrot¡tsI
cl?cttttl rllt, sQ ft
tuiDt¡ o? l¡fnll PEris '
ttln Pttf Il¡¡ pt¡(
t959 598 1960 533
t96l 8?6 t96r 213
t96t 759 '1968 151
tgtt 507 1972 1t5
t9?5 5¡8 1976 623
lltf - 087 sîD. D?t, -
lolls:
'122
t8
ItlP ¡E?lRlIcE ! f¡9:088235
ÞEIIOD o? Flc. - l95q-76
IB¡N PBIÍ ITTA PDIÍ
1961 366 1962 120
1965 355 1966 59C
1969 284 1910 339
1973 326 197¡ 259
200 COEF. OP SßEÍ = 0.09¡5
t, rtB 1936 PLOOD PAlf, Op 98C CtrrECS tts Trlrt ts TRE
stcofD Llf,otlir rt îEE pEnroD 1899-1977.
c¡lcctltf trEf,, sQ ft - 189 ltP ¡Et.!nBfCr Ê !19:553051
tltfDtfF Ol lrloll Þulis . I P?¡IOD DP rtc. . t96l-60
ttl¡ Prtr fElR PEtf( YBts Ptl¡ tlln Plri
195 1 2.t3 1962 211 1963 113 r96t t?l
I 965 212 1966 285 196t 27! 1968 2t5
iltl = 222 sTD. DZu. = 6t colr. ol srP¡ - -0.5óll
slrr 46612 fíl¡lPl¡t R lI st B¡ÍD6E
CÀÎC¡liElT tREt¡ SQ Íll = t62 irP AEltEElCl - a20z102l92
fúiBEn OP rll0ÀL PEtrS = 11 PE¡IOD Ot PUc, . t960-76
:I::______::::l
¡¡IttI B tî ioTtots IE¡R PETf, rglR PETI( IEÀ8 PETT ttl¡ Pt¡f
1960 I 1r¡ 196 1 I 1¡ 1962 t28 t!t63 r05 ¡
Cltctllll lRll, sQ Íi Ê
196¡t â9 t965 1tt 1966 29t t967 103
69.9 lllP ¡EIEFE¡cE
l0llr¡ oÈ trl0rl, DE¡ßS .
¡67:799¡30 1968 2t2 196 9 235 1970 111 l9r I 3t9
r0 PEaIOD oF FPC. = t967-76 1972 15¡ I 973 370 197r¡ tr9 1975 159
1976 ?50
ttlt PEIR tBln PEtÍ IETR PETT IIIR PETX
1967 58 1968 70 '1969 2g 1970 q6 lizll STD, DEf. -
1971 30 1972
= 184
97 cogl. oP sREt - 0.6lll
36 l9?3 25 t97rt 38
1975 38 1976 55
ill!. ¡13 sfD. Dll. . 16 CO8F. OP SÍE¡ . 0.?¡65
sIlE 4666C
PUtrElO¡OT R ¡T PTÍITI'TOT
ClTcñtlElll
s¡!t
tR?1, s0 Ãll
PIPIIIIRT 2.08 llÀP BEP?REllc?
& = f19:5830(2
T1 SE BIIDGE ItrllBER ol tllfttll PE¡I(S = 12 PERIOD Op REC, . f965-76
IE¡R PETI( YBI R
CltC[lltl llltr
PBT( TETR PEIX
S0 f,i ¡
I!¡¡ PBIÍ
51 ãlP nElraEIct I
f 965 9.77 I 966
rûill¡ 8.rr7 1961
OF lllorL Pl¡Ís .
t¡?:¡23382
10.75 t96B ¡,70
PEnIoD oF R?c. = 1970-77 1969 1,18 't 9"0 17,28 t9?t 5.72 1972 8.76
t 973 6. Ê5 I 97q 1
tll¡ Itlr tE¡R
1.65 t9?5
Pttß
15.81 1976 9.05
lEtn ÞEÀr IE¡F PETT
I 970 ¡9.8 't971 ¡1.9 1912 35.0 1973 2¡.
15.t
I lElI
t975 95.0
' 9,72 STD. DEv. .
I 97r
3,7< COBF. OP sXEc
1976 ¡6.5
= 0.912t
1977 11.2
iBll - 39.9 sTD. Dtv. - 26.3 coBp. o! sßEr . 1.317¡
!t152'l
0Pr8r R rî Poffi
srrt t5702 ¡lrrSIIt R ÀT Dollt S¡lDOr
cllc¡il¡Î tREt, s0 Í! - 8.03 nrp REFEAE¡CE - ¡3q:tt?209
l0;¡l¡ ot llfltll P!¡fS t l0 PERIOD Op aEc, = 196¡-?7
fEl[ PEtÍ tBta Pllß IEIN PETR tEf,R DETK
t968 27,70 1969 29,35 r9?0
1972 tt2.60
21.35 19"1 St, tto
1973 2a.20 197¡1 8. 80 1975 38.20
1976 67,r0 1977 26.60
tllf . 32,73 STD. DPl. = 15.7¡t coFp, oF sKE¡ ' 0.936ß
torts ?
l. LttD ûst cEltgtD It 19?¡ ?ROr cB¡Ss 10 Exorlc loRasl
ottt rBo0l 601 o? TE? c¡ÎC8iErt, lBB EptRCI O! TEÉ
PO¡ISÎ 0f Tf,t ?Lot ?toÁ 191tt-77 ¡Às ltoT cofsIDERFD
10 Et slctl?IcrrT,
Cllc8it¡T tREl, sQ ft¡ = 10.6 ñtp FE?EFEIICE =
IlrllBER oP t¡lltÀL PPÀXS = 12 pErIoD ,p iEc. .
il5:2 313¡E
1966-71
IEÀR PETÍ fEI R PEIT IETR PEÀß
'1956 lEtn Pttr
t63.3 146? 4q,5 t968 51. r t969 10.5
1970 28.9 tg?l 2r¡,5 1912 25,9 1971 10.9
t97¡ lq. c 1975 56. I 1976 26.1 ,t971 19. 5
lEttl = r¡1.9 STD. DEv. É 41ì, I CO?p. OF Sßpt - 2.7595
ÙoTES:
l. THE 1q66 pLOoD nEltr ta¡s Io? pLoTlEfì ol|DÌp nûLE xo.2,
BÛ1 rts IÙcLttDpD II îHE !ìEFM'IIOI CF lEn GttlRtl,rsDD
CUEÍE POR îNE I8PI.
18. NORTH ISI-AIID WEST COAST DATA
slrr 166 I 1
f,¡rEo R rT Gotcr slrt 3310t
cEltGrEEt F t1 ñÀütIcÀRo¡
cllc¡lltT r¡lr, Se rr = r16 årp REI9EEXCE . rt9:206912
lolBtn Ot rtfoÀL PE¡ÃS E I pE¡toD op Frc, ¿ lg?,Û-'7
ÍEIS PEIK IEÀR PITI(
1972 203.3 r9?3 151.4
1976 100.0 1911 1 0?.5
ll¡¡ PEt[ tBt¡ PEIR
19rO 181.6 1971 138.3
t97r 65.3 1975 89.3
iltr ¡ 139,6 STD. DEy. . ¡l¡,8 COEF. OF SiEt = -0,¡271
totts:
l. tEE t962 ?¡,OQD pElK Or 303 CLËECS CtS ltxEi tS TíE
LTRCZSI ¡f TflE PERTOD ß61-77.
c¡lclr8lî ¡nl¡. s0 ri . 19rt
lútBtl o? ttfttÀL pzrÍs - ß
tzt8 PEt[ IIIE PE¡Í
1970 467 t971 ¡8¡
t97t 6¡8 t9?5 640
llll ¡ q85 STD. DE..
l¡P BEPEREIICE . tr1:lF:?9087q
PE¡IoD 0F REc. - 1970-77
IEIR PEIß TETR PE¡r
1912 326 1973 t3e
t976 558 1971 316
127 COP,?. OP 'sREr - -0. 0f95
totts:
l. t¡t t96t FLq)D pE¡r Op l¡08 coiEcs tls ÎÀKEI tS
în? LÀrcEsT r¡ Îf,E PttIOD 1936-?7.
sITt 466 18 itf,crKl¡trt R lt €olBt srrr 33103
TÍI|G¡EIII' R ÀT SN .ì BRII'GE
cr?cHiEùr r8Dr, sQ Kt =
luiBPn oP rftotl PPtK:i =
IEIR PEIÍ
1961 0¡7
1965 40t
t969 48?
1 9?3 2A9
'1977 3tt2
iBtL = ll5 J
rBt n
1962
1q56
19rC
l97q
PPIÍ
961
808
395
378
246
11
¡rP REFERTICT f19s366077
PPRfoD 0F REC. = 1961-71
YEIR PEIi IttE Ptlf
1963 2r7 19ór tó8
196t 190
19?t 382 .1972 t968 ¡t6
t29
1975 643 19t6 t80
sTD. DEl. = 21\ coEP. oP srtt . l.ttt¡
lolBs:
l. ?n9 t962 ?L(þD pEÀf, tls T¡f,Ef ts 1[r L¡8GESÎ
If TID PERÍOD 1959-77.
94
CllcBllll tllt, sQ ri s t968 l¡P AEPIRE|CE . ìrr¡3:689t76
ll¡lll¡ Ol Àrrt¡L PEIIS = 7 PE¡IOD ol REc. = 19?0-?6
tlt¡ Pllt IP¡N PEÀK IEÀR EETT IBTR PEÀtr
t9?0 50t 1971 rt56 7972 3t1 r9?3 ¡33
19?t 680 r9?5 722 197ó 5û9
lEtl ! 522 SîD. DEt. = t¡3 coBr. or strE¡ E 0.1212
tolts i
1. lrt 1961 tLooD pt¡tr op 1168 ctiEcs rts TtrE[ ts
lil LrnçtsÎ tt lEl p!ÌIoD t935-77. otDla BûLE ro.1
otlt t[¡3 ptlt tot T¡¡s stTE ¡ls oslD tt lEr
¡to¡ottL PLor ¡lD It ?Et DERITÀTIOi Ot ÎñE
cErlttl¡stD ct¡tD tot rEB lnBr,
Water & soil technical publication no. 20 (1982)

stlt 33101
crtcltttr
lûtBlD Ol
t¡El, s0 Ír
llfoll. PEIf,S
=
=
539 tÀP RA?ÊRE¡CB = rlll:?78308
13 PERIoD 0F REC. r 19ó3-75
SIlE 3l3lr
CEI|GIEXI' I TT ÍIRIOI 3f109
CrICE;llÎ r¡lr' sQ rl =
fltltl¡ oF lft0ll Pll[S =
q92 ItlP ¡EFEREICt = I131:965389
10 PEnIOD oP REc. = 1963-76
tll¡ Pg¡f, rtla PElf fEÀR PBTÍ IBIA PBIT IU IR PlTÍ
196¡ 83.80 r96¡ t20.35 1965 112.19 1966 97. ¡9
t96r 't21. 35 1968 86.8e r969 65.06 1970 82.84
t97t 93,90 1976 r01.50
tlll = 96.54 SlD. DEr. - 17.93 colP. or srEt = -0.0964
::::--_-- _::: ll
I|ITGICNPEO R IT ORB ORE
tt¡t PEtr
t963 r{9.35
7967 296.00
19?t 208.00
t9t5 345.00
llrr = 2¡0.28 stD, DBY, =
:r::_-____::1::
CtlCElErT lEtr' S0 I! 63.5
lolDl¡ Ol llllt¡l Pltfs = 9
IITD PBTtr fE¡R PEIK
t968 5.69 t969 3. ¡9
1972 5. t0 1973 3.39
t976 4.O7
lll¡ = 4, t8 SÎD. DEv. =
srtt 311 15
IEIR PEIß
t964 207.00
1968 162.00
1972 153.36
CItCE;llT tBBt, 50 frll 33.2
fltlBEl oF tltttll, PPÀrS = B
ftl8 PEtÍ rEI¡ PETK
1969 9.2tt 1970 I 8. C0
f9?1 1¡-49 1970 22.97
iEtf = 19.68 S?D. DSV. =
srtt
3lt t7
¡IITÀXGI R TT TIIGIÍII
C^TCEitlll rREf,r 5Q Kú =
ItiBFR OP tittÀL PÞt[s =
c¡lcnllExî tREt, s0 Ktr =
¡I'IIB?R OF TT[UÀI, PETKS =
TEIR PT¡T YEI R PE¡K
SIÌT 333 16
c¡TcftfFlt? rREÀ, SQ Kü =
IIUiBPR OP ÀÙXI'ÀI, PEIÀS =
tu ÀR P9Âf
PETK
1962 3tt¡.66 'EIR 1963 168,88
1965 zit.92 1957 393.39
1970 27A.57 1911 31q.71
197q 365.00 1975 3s6.00
lEtX = 324.77 sTD. DEv. =
J32
15
it¡€tlol-o-Tz-to E lt ¡!¡¡ortt
ll¡P RE?ERrlcE t12't.72t621
PEnIoD oP nEc. = 1962-76
YEIR PEIÍ IITR DIII
19611 463.47 1965 q10.35
1968 317.57 t9ó9 r93.t8
1912 266.59 19?3 2t.t.90
1976 332,00
82.61 COPP. OP sil¡ ! -0.2315
IBTR PETf, lBln PErr(
668
1965 256.00 1966 204.00
l5
r969 1t5.75 r9?0 29 3. 00
1973 112.21 1974 362.00
YPÀR PEIÍ
1962 .251,61 r96l 190,87 19 ó4 402. r¡8
r 966 229 .',10 1961 20C .7C 1968 259.79
8r¡.73 CoEF. OP StrEr -- 0.2112 t9?0 213.35 19a1 233.1¡ 1912 233.10
1914 239. R3 1975 130.22 1916 207.25
ËE¡il = 268.21 SlD. DEv. -
ËlP nEIERZùcr = t1222011811
PERToD 0P R¡c. - 1968-76
IEIR PEIÍ IETR PEÀK
1970 3.75 1971 {. rl
197q 3.74 19?5 3.90
0.77 coEF. OP sÍEI = f.1780
lllxct?ToRot a tT scflool
lÀP ABPEREIICE = Xl21:743458
PERIoD OF REC. = 1969-76
YEÀR PEIX
PEìß
1911 20.01 'PIR 1912 13.52
1975 28,32 t976 30.50
7.35 COEP. oP sf,E¡ = 0.2075
ñÀKOlI'TÛ R IT SB II9T BRIDGF
CllcEiE¡î rRPl, S0 ri = 21,8 ttlP RETERB|CI = X121:83rt547
IolBlE OP t[X0lL PPI(S = I PEIIOD 0P FEc, = 1969-76
tllB PEri IE¡R PEIX rEtt PllK IETR PETT
1 969 1 8.63 1970 26.49 1f171 21.46 1972 1 8. 50
1973 15. ¡t 't 974 33. 05 1975 16.24 1976 30.8n
lEti = 25.12 sTD. DEg. = ?.70 ConF. OP sR¡r = 0.221q
19n3 412
1967 2!A
1 971 1C6
1975 32tt
ãElL = 259
r7t 8
196 tr
196n
191 2
197 6
oE0m R lr Îofo¡Itì
r¡P iEFEFB¡cE - lt0r:556097
PERIoD OF PEC. ' 1962-76
tEtB Pt¡t
1965 ¡09.2f
1969 t85.2¡
'r973 r 1t.62
80.r¡1 coEP. of sfE¡ = 1.0021
otctRrrE P l1 tl8ltc¡iúlo
1C?5 t1ÀP nBPIREÍCE = tt01:751165
1l¡ PEPIOD CF REC. = t953-76
PEÀf,
24t
224
284
245
STD. D¡9. =
YEIN PEIi YE¡R PIIi
1965 330 1966 2ta
195c 162 1970 21A
1913 21 J 1974 212
6¡ CoEF. oF sf,EÍ = 1.0385
lÌolEs:
1. 1H!'t9r¡0 FLOOD pE¡K OF 525 Cril'ECS CIS IIXFI tS lEE
SECONT, I,ÀPGF5T IlI TIIF PîRIOD IAO5-"".
srtt 3332c IETTIPÄPT R IT POOTBRIDGF
C¡lCBfBlT tBEl¡ sQ Ãl = tBt¡ llÀP RtFPRFI¡CE = N111:960859
ÍtlBER OF Àfi0ÀL gEl¡s = 11 PERIOD oP REc. = l96C-76
IETI PBTi
P?AK TEÀR PETK YEÀF PETÑ
1960 26tr.61 'EI[ 1961 419.05. 1962 296.25 t963 369.56
196¡ ¡63.39 1965 563.00 1966 446.93 t967 532.3¡
't968 ¡12.19 1969 3r8.0C '1970 246.68 1971 5q2.40
1972 417. t4 1971 2q5.J5 19?q 230. 15 1975 259.68
,1976 399.6¡
Illt = 382.08 sTD. DEY. = 108.03 coEP. oP strEI = 0.1963
torts:
1. ¡O COITECS ETS BEEI TDDED 1O ETCE PETK TFTFR 1972 10
IILOT POI lNE EF'ECIS OP lNE ÎOIGTRTRO PO9EE PNOJECT.
31301 ctlctilol R lT Elt?lfl
clfcfillEIT ÀREÀ, 50 Kll =
NUll8rìR oF ÀI¡tttL PEÀKS =
YETR PEÀf
PEÀI
66lll
t9
1958 3960 'BIA 1959 1q80
1962 2330 1963 11?C
1 966 20F0 1957 2610
1910 1r¡80 1971 2390
197t¡ 3100 1975 318C
Ittll = 23!7 sTD. DEÍ. =
ËlP REFEFETc! lt38:56?055
PERIoD 0P FEC. = 1958-?6
PBIf,
PBIÍ
'EIF. 1960 1830 'IIR t96t 22AO
196{ 29 30 1965 33¡0
f968 2840 1969 1040
1912 t8t0 r97! 2630
1975 19ß0
?76 coEr, o! srtl t 0. t601
IOTES:
l. 4C CUIECS 8lS BtEt tDDEt, lo ercn Ptli rPftl 19?0 IO
TLIOU 'OB
TEB EPIBCTS O? lNE ÎOIIGIRIRO POÍBB PI(NIC?.
333 30 ltlcr¡of R lr ËrTtPr¡fl
CrrcEllrf t8lt¡ SQ f,ã 911 ¡¡P RBFEFEHCP 1t101:81510(ì
rotDrB OF tilfrtl PBtf,S = I PDBIoD oP FEc' = 1965-?2
IETi PPIÍ YDIÀ PEÀI( TEIS PETf, tEÀ8 PATÍ
1965 862.95 r966 693.73 196? 659.?9 1968 407.93
1969 258.95 1970 372.06 1911 s71.26 1972 591.26
lErt - 552.99 sTD. DEY, = 196.31 co?P. oP sÍE¡ - -0'0130
IOçt5:
1. ÎÍE ',l9r¡o PL(þD PEtÍ OP 1628 COIBCS ¡ÀS rÀRFr ÀS TfiF
LrRGrSl Ir TEI PIRIOD 1905-77.
2. l0 cùrPcs Rls B9B¡ tItDBD 10 fnE 1972 P?li 10 TLLOY
lOB ÎE' ITTECîS OP TEE IOíGIRIBO POÍEN PBOJBCT.
13t02
srfc¡fot n ¡l 1l lllll
cÀ¡CElE¡r rREÀ, sO Íü 2212 lttP RETEBETCE lt0ls?050ó7
¡lttBEB oP rlt0rL PU rls = 14 PERfoD ot RBc. - 196Þ76
fE¡B PEÀ¡ IEIR PETÍ YEIR PErr ttll Plll
1963 ?l¡9 1964 1160 1965 1213 1966 t00l
196? 869 1968 7q6 f969 r42 l9t0 619
1977 851 1912 7tt9 1973 871 t97a 560
't9?5 843 1916 679
It Eli = 818 sTD. DEv. = 221 co'l. o¡ Sitr . 0.5176
LOTEs 3
1. 40 CUãPCS ÍÀS BEZX ¡DDED 10 E¡Cñ PE¡f, rPrER 1971
?o trlor PoR 188 t?PtClS OP TEIÌ lolclnrRo Poltl
PROJECl.
2. lHE 1940 FLOOD PEltr OF 2294 CtlEcS ¡lS TrfEI lS lll
LÀRGESÍ TT THE PIRTOD 1905-77.
:Iï-____::991
Water & soil technical publication no. 20 (1982)
POIPHI' R ¡T PIEI;T
C¡ÎCEÉtlT ¡BEt, S0 ßl = 29.5 útP BE"EFEIICB Nl28:5C7187
lúlBtn Ot Àttltll PEIIS = I PERIOD o? REc. = 1910'17
ttl¡ PBtf IETS PB¡K IEIA PEIÍ Y¡ÂR PEIÍ
r 9?0 25.3 1971 33.5 1912 21 -3 19''3 l?. 1
t9?¡ 26,7 19?5 ?9.0 1916 64,8 1971 111.8
Íl¡l . 39. 5 STD. DEt, - 2't ' 6 coE?. oP Strt = 1.1{41
¡otts:
1. tSrs sllllol ¡ls rol t¡sED I¡ luB Rlsrortl. lllÀLlsls
BlclttsB ol Drslrlcr 0P¡tRDs cttRYllûnB rÙ 1ÍA
PiOEIBILITÍ PLOÎ, ¡ TREÍD iTBKEDLI DIF'E8EIT TO TEE
RBCTOiTL OlS. r1 tls ûllcll?lr8 lÉETllPR Tñrs l^s ¡
RrlL DIPFEREÍCE, TXD îtrBEEPORE POSSIBLI I¡DICITIVE
ot TEE riPr.ttB¡cE oF lT, Ecloll, on sIiPLr TIR
ttsûLr oP osllc I sroRl RFCoRD-
95

3950't
flrlÀRt R tr îlt¡Ît
;tP RIFEFEICE . Il09:92t805
PlSIoD oP Fle. = 1969-76 stlt 3r801
"ar""r"rn ttrl¡ sQ ßt . 725
tlttt¡ o? trtotl. Pzlks - I
rtlt PEtß ttlR PEIÍ IBTR PETtr TEIB PEIÍ
t969 ¡51 19?0 q90 197 t 9q4 1912 t¡10
l91t 5?8 r97{ 59t 1915 568 1976 114
llll . 593 STD, DEl. = r70 CoEr. oP siEr = t.3ltto
tolt3:
T. ?EI T97I PLOOD PITÍ TI5 TÀilX 15 THF Lf,EGESl
rt iE¡ PErroD 1900-76.
Cl?CElEll l¡El, Sg Íi t 80
IûlBll Ol lllltlt. PBlrs - 12
ttl¡ Pgrf tElR PPIÍ
7962 110.97 1963 16r.09
1966 rf5,7¡ 1961 236,97
t970 203,66 19"1 2tr0.23
llr¡ . 17q.57 sTD. DEv. =
srrE
l¡343-1
cÀlcRiEIT ÀREt, S0 KË =
tolBEA OP ÀIl¡UtL PEÀXS =
YEÀ8 PFTtr
1 970 587
I 9?q 3{0
lEtx = 41?
srrE 43015
TET F
t97t
t9a5
SlD. DEÍ. -
2826
PETT
332
370
cÀlCRlrIT ÀREt. S0 [i = 137
úllllBER oP rñ¡UtL PEÀI(S = 13
IEIR PETK IEI¡ PEÀK
1965 43.9 1966 46.6
1969 25.9 r9"f 55.1
¡973 10,8 r9t0 35.9
1977 55. s
iElf, = q5,2 STD. DtlV. E
F
::t:llT-r_lr_lIII]_::ll
ntP REITREtlcE . ¡10q:0¡3?27
PERIOD 0P lEc. = 1962-13
tFtR PSIß
196q 137.6C
'1968 113.62
1912 141.24
YETP PFTF
r 965 2 69.9 I
rc69 1 33.61
't9?3 78.0c
55.10 COEP. OP SKEI - 1.1907
fllPr ¡ lT tttllttllt
ËlP RETEBE¡CE ' 165:5ó¡¡56
PERIoD oF FEc. ' 1970-77
YE¡N DEIX I'IE ÞI¡f
1972 4t6 f9?3 tS2
1976 576 1977 362
104 coEF. OP SÍEB a 1.2112
lC. IUIAÍTAWATU-RANGITIKEI DATA
c\rcrlrrr t¡rl, so rt -
301
18
lotDtB o? ttttttl. pElfs .
tBr¡ PEtf tEra PEIß
f958 tt25 t959 1t3C
'1962 1360 1963 65r
t956 558 1967 t¡?0
t970 59¡ 1973 991
r9t6 1250 1917 690
lElf . 970 srD, I,EY. =
tolls:
o?lrr I rr rotPtft
ilP lErgBttct 11512119192
PERIOD 0P REc. = 1958-77
IEIR P'Itr IEIP PE¡Í
1960 t0t0 1961 1130
196tt 1 r90 1965 1580
1968 1090 1969 1020
197tt 615 19?5 711
339 COt?. O? sfPl = 0.0865
1. rltu¡¡. tlooD Pstf,s poR tlrE GoRGt srÎE,3t80l, crRE usED
tol lit ÞtRtott 1950-??.
2. 18t t955 pLæD PElf Op 25¡0 C0;ECS lts TrrEi tS ltP
LltGBSl rl ÎfiE PEnIOD 1920-17.
3. lo tr¡oÀL PrtÍs ¡BFE rvrILrBLB roR t971-72.
srtt 32502 itft¡tÎû R l1 FrrzHERBEnl BA
Crlciil¡l lglr, S0 Rl . 3916 ñlP REPERE¡CE x1¡9:115331
IEIEE¡ Ot tflûr'. Petls = 49 PE¡ÎoD oF FEc. = 1929-71
tBt¡ gElf lEli PErß tErR PErt rEln Ptlf
1929 1655 t930 1450 1931 tr50 1932 1795
t933 t 4 t0 1930 1280 1935 1850 1936 2580
t937 755 1938 1625 1939 1850 1940 t280
l9lr 3260 1942 2090 t90l l?t5 190t t2q0
t9¡5 2335 19¡6 1700 1947 2580 19t¡8 2000
t9r9 2'35 1950 2045 195'1 1110 7952 t¡to
1953 r5¡5 t95¡ 1284 1955 1810 t956 3t85
t95? 1565 r95B tq90 1959 1715 t960 950
t96r 2110 1962 950 1963 12¡0 196rt 2580
t965 33¡5 1966 1110 1961 t765 1968 t380
1969 560 1970 1060 19?1 2235 19a2 r33o
t97t 930 t97q 1380 1975 t4t0 1916 2380
1977 1260
cttPtPt I lcl¡otl lolD ll¡l - l7¡8 SÎD. ItEf. = 7¡¡6 COEP. OF SIEÍ = 1.50¡¡2
¡otts:
lltP ¡EltRElcE = tgls 15t820 l. rtt t953 rl(xtD PErf op r¡5rr5 cnãEcs cts TÀfEf ts Tf,E
PEIIoD 0P ¡Ec. ' 1965-77 Lltersl Ir In¿ PBBIOD t88t-1977.
2. t¡t t902 rL(þD PllK ot ttotr cuitcs rts rlrE¡ rs 1ñg
rEÀR PEIÍ rtlR Ptlt stcotD LlteBsr
1967 55.5 t96g
It 181 Pt¡tor, 1881-t977.
31.5 3. llru¡l.
1971 5q. q
?LooD PEtf,s FoE ?f,E
1972 rr.2
¡olflrfE slnEEl SITE
(fo?325801 9ERE oSlD toR TRE
1915 58.5 1976 51.3
pERrOtr 1912-77.
11.2 coFP. oF sßE¡ - -0.1091
srr! 32503 IttlftTrr R À1 IEBES Rotrl
s1îE
r0ql427
CtTCllñPlÎ rREÀ¡ SQ (l =
TOiBER OP TTXf'ÀL PEIKS -
IETR PETI( IEIR
t96q 62. r 1965
1968 58,3 1969
1972 11.A 1973
1976 51. 9 ',1911
iErI -
IAIIGTÍIf,O R TT DTÍLOI IOID
373 ñÀP REPERgIIcE = f8t!22l7tl
'14 PEBIOD 0l AEC. - 196U77
PETÍ tETR PETT
51. 8 1966 6¡. q
Ir1.? 1970 69.0
53,2 197q ¡9.2
65. C
tll¡ Dtlf
196? tl.0
197 I ¡7.3
1975 ót.5
CIlCE¡lfT lRBt¡ SQ Íl * 713 ilP ¡BllREIct = fl50:5?3q91
f0llll ol Àlt0ll EEÀIS . 22 PERIoD Ol REc. . 1955-7?
Ilr¡ PEIK IBI R Etlf ISIR PIIK IEÀ.B PIIÍ
t95s 905 1956 960 1957 ¡95 t958 395
1959 625 1960 255 t96t 560 1962 550
t963 ¡60 196¡ t?5 1965 6t5 1966 530
1967 ¡75 1968 Slao 19?0 225 1971 1015
1912 520 19?3 315 r9?4 ?40 t9?5 320
r9t6 ¡70 1977 4t0
llll - 539 gTD. DlY, = 23¡ coE?. oF sxE¡ = 0.5673
rofts:
1. ¡O lt¡tttl PE¡t ¡rs rtÀILtBLr loR 1969.
srrE 1C03461 lOfEÀRfRO R IT TPPII DI'
3251t¡
OEOTII R ÀT ILIIf,DILE
c¡rcHlBll rAEÀ, S0 Ktl = f7À ¡¡p RB?EREICE - 1112a23672O
llollBFR OP t¡ltt^L PEIÍS . 17 PERIOD Ol RBC. ! 1960-?6
Prtf IEIF PEIT YEII PEri ttll Ertf
198 1951 134 1962 198 t96l 222
350 1965 228 1965 292 19ó? ¡81
1{0 1969 246 1970 260 r97l 252
't32 1973 108 t97¡ 264 1975 224
264
I EÀA
1960
I 964
t 968
1912
1916
IBlt =
241
STD. DEY. = tl cosP, oF s[E¡ - 0.3ó96
cttc¡tttl rtlt, s0 tt =
lplllr Ol llllttl. PBlfs =
tt¡¡ PBrÍ ttrR Pr¡f
t95¡ I t0 1955 155
1958 125 1959 135
1952 t70 t963 225
'1966 190 1967 260
t9?0 215 r97t 220
197a 100 1975 250
ñlll.
lgl STD, DEl. =
293 itP REI'REIICE = f,100:148573
2I PEEToD or PFc. - 1954-77
IEIN PEAT TETR PET¡
1956 32C 195? t45
1960 70 196 r 100
t964 55 re65 325
1969 225 1969 r05
1912 t80 t9?3 135
19?6 17C 1911 r15
89 COEF. oF SKEI . 0.95¡8
srlE
rc43(65
grrfloÍoffr R tT DBsttt lorD
ct?cBiE[Î tRst, s0 ßË = F8 rlÀP RE?ERElcE = t112r221715
¡lliBER Ol t¡rrtÀL PBIÍS - '14 PERToD 0P ¡r:c. . 1962-76 cllc[ll¡Î rlEÀ¡ SQ fl = 266
Iolll¡ Ol llloll PE¡[s = 24
I ttR l,ETÍ TBTR PEII( rErR PnÀÍ tÄn Pllt
t962 46.0 1963 10.2 1965 09.3 1966 37.5 lltl P'If IEÀR PEAK
I 96? 55.1 'to68 ¡r9.9 1969 1973 53.8 19?0 7t0 1955 26.4
39.0
1 95¡
152C
1971 62 5 1972 q6.8
t9?¡ 28.9 I 950 385 1959 1305
1975 53.6 tq?6 63. q 1962 705 1953 685
1 966 580 1961 720
iBli = l¡7.5 STn. ÞPY. . 11.8 COPF. Ot SfSl - -0,5\22 t 9?0 a20 1971 7ss
I 97r 730 1975 600
IOlES !
I. TO ITf,UÀL PETi TTS ÀVAILÀBLE IOR 196I¡.
lllf. 719 SrD. DEr. =
96
srll
t2326
Water & soil technical publication no. 20 (1982)
IÀIIGIEÀO R ÀT BILL¿¡CD
ItlP REI¿REICE lt49:2?0251¡
PE¡IoD Op RÌC. = io54-77
PETÍ YgTR PETÍ
'E¡R 1956 235 1957 620
1960 89C 1961 305
1964 10!C 1965 60n
1968 FlS r96q 6?0
1972 9tC l9t3 110
1976 7U5 1911 ¡¡50
29d coEP. oP srB¡ = o'961R

SIlE 12 5 2!ì frRÀotll R ¡1 tc¡lnt¡r 3270ß RÀIGIITTEf B AT SPRTIGVALE
cÀÎcñlu¡l tR?I, s0 Kr =
xutlEFR 0P À[ilúIL PErxS =
P¡ÀK TEIE
IETR
l95r¡
1 95€
1962
t 966
1 9?0
1 974
ItEIX =
734
PEII
1rr5 1955 310
250 t959 315
160 1q63 195
265 1967 325
295 191'1 350
315 1975 295
262 sTD. DEY. =
IttÞ REP?8EICE . l1¡9:392215
PEIIOD oF ¡Sc. = 195¡-t7
IEÀR PETI ttlR Ptlf
1956 10 1957 155
1960 s5 r961 610
196ra ¡30 't965 335
1968 215 1969 75
1912 t50 1973 2ts
1916 370 1971 310
128 coEF. O? SKEÍ . 0.3?¡8
cltcÍlBllT t[EÀ¡ SQ fl = 583 lllP EEPEREIICE , [123:50?q16
rttBlB oP Àittttl PEtfs = t0 PBEIOD 0P RFc. = 1964-71
IIIR PEIf, TEIR PEIÍ IEIR PEIX YEIR PEIII
t96q 530. r0 1965 30f.0û 1966 382.20 1967 rr3?.31
19ó6 249.2A 1969 203. Í5 1910 30 t. 01 1911 284.66
1972 3r0.58 t97l r9?.33
lBrf = 322.6? stD, DEv. = torr.24 cotP. OP SÍlc = 0.79?¡
srtt 32723
rro¡cÀRrûPr R rf Pont¡t RotI)
2\
rll¡
s Ilr
325f1
ClrCEiE[1 rREÀ' SQ Kl tt52
ùlrlBER oP rxIûll ÞElf,S = 24
IETR PP¡I( YETR PEÀK
1954 Cr¡o 19,

S ITI 29202 RuNttiltcl I ¡t tllEttet
cllcE;!¡I tnEl, S0 fi È 23qC rtP REtERFtCt r t16t:91¡t29
llu;Bl¡ O? lfllttL PEIßS ! 2l PPRIOD OF REC. . lt57-71
IETR PEIÍ IEIN P'TÍ YEÀR Ptf,f tllt ?tlt
195? 630 1958 1025 1959 765 t960 lr0
1961 t050 1962 82C 1961 7¡5 t96t rt!0
t965 1075 1966 tllC 1967 850 t960 r00
1969 .585 1970 t02C 1971 1 r80 1972 97J
1973 6q0 r97q 935 r9?5 980 1976 965
1971 t t60
ñEltl = 896 sTD. DEv. = 211
CorF. OP Sßlr . -0.619¡
2.
stll
BAY OF PITTTY OATA
It6t0
crtcEllt¡Î t¡tÀ, sQ fi l0llDlF ot llloll PE¡fs .
tEl¡ PPtx frt¡
r960 r1.58
1972 18.2r
1976 27,35
iEll. 2C.10
PEtf
1969 13.95
t 973 r 3.85
SrD. Dtl. .
57
9
nllrtlrt ¡ lt s¡5 ¡ttDel
ñtP ¡EttRttcl . 176t71O032
PERIoD Ct l;C. = 196;-76
YglR P;lf rrll ztll
197C 21 .18 1971 23.t2
1974 35. ¡6 t9t3 t3. t¡
7.81 cOtF. O? 3ßlr . 0.r0t6
s rlE
2922r
CtlcEllllÎ rEEl, S0 Íi . 183
XttrBER oP rrlútl PEtrS = 22
IBIR
1 955
'1959
r963
1967
197 1
1975
ñE¡I =
P¡|IK
PIÀÍ
223 'E¡B 1956 81r
?30 1960 42tt
'.37 tq64 ¡71
110 1968 555
42t4 197? 322
400 1976 566
532 STD. DEc. E
srrr 29231
¡troBrtE ¡ ¡1 €otel
lltP REPEnEtcE I161:90?508
PEFIOD Ot REC. . 1955-76
ÍPÀR PBrtr tt¡t Ptlf
1957 156 1958 l9r
1961 ¡¡56 t962 68t
1965 531 1966 7r0
1969 537 t970 r?3
19?3 662 197¡ ¡56
'147 coEP, ot StrEt . 0. 1738
T¡OERO R IT ÎN TIRIIîT
s¡1t l¡6 r¡
ctlciltf? rMr s0 Ít ¡
tüllB¡ Ot ¡ltorl PEIÍS B
tEtB PEtf ttt¡ Pt¡¡
958
21
ftrlllr¡
R rt tl tlttl
ilP ¡trt¡ErcE . t67ttt2¡59
P'BTOD o? tEc, . 1956-76
frl¡ PEtt( ttlt ¡lll
1956 22a 1957 69 t958 t'r 't93' l?a
1960 102 196 r 98 1962 368 1963 77
t96¡ 12 1965 96 1966 86 1967 27O
196e 116 1969 12C 1970 187 19?t r!0
1912 150 19?3 12 r97¡r 122 tyts 96
1975 r r0
lllt - ll9 STD. DEt. È 74 coEl. oF SÍEl . 1.t:mt
toÎts:
l. TtE OüÎttî pBOi Lr[t ¡o10r1l rs 38,8Ri opslrrlr.
CllC8ltfl tllr¿ SQ lf -
r¡t{llr Ot tlloll PIIIS .
tttt Pll¡ IEIR
t9t0 r15.0 191 I
'19?¡t 211.0 1975
.llll ' 156.0
sttr 29212
STD.
PIÀÍ
3?3 llP REItREIIcE = ll62:239578
I PERIoD 0P FEc. - 1910-'11
YETS
203.0 1972
t?t. c 1916
Pttf
41.9
173.0
;trGoREr¡ R rT slúrDtlJ tllt
IETR PE¡I
t973 87.9
19?7 225.0 c¡lcÍill ¡Elr sQ fl ¡ 179 rllP lltlPBlcE . 167r8l6¡ta
¡ltlBtR Ot ltl0ll PE¡fs = 9 PrRfoD or ¡Ec. - 196ç76
ttl¡ PEtf fB¡n PETf tt¡R PEt( rtll Pt¡¡
t969 292,0 1969 86.0 r9?0 t57.0 1971 86.0
1972 10¡.5 19?3 53. 0 r97¡ rç0-0 1975 12t.0
t976 222.0
rll¡tlrtflt R rT iÎ Eo¡,DStORlt llt¡ Ê l¡6.5 sTD. Dtt. ¡
76.7 COll. oP sfll . o.totl
ctlclltfÍ rr!t, S0 fi c 38.8
l0ilE¡ O? ¡lf[rl PSIIS q
=
ttll ?ltf ttlR PEtÍ
ttó? 63.9 '1968 r0.5
r9?1 76.8 1972 t 55.2
t975 173.2
rl¡l .
srtr 292¡f
89.0 Sllr. DlV. r
cllclittT r¡ll, s0 tt .
tltl¡t¡ o? ltfoll. Pr¡3s.
36. 3
9
lt¡t tEtf tttt PBI¡
t968 2t.20 1969 7. {9
1972 2t.80 1973 ?9. 80
19t6 2a.29
Itll . 27.56 srD. D!t. .
itP BIFEREICE = !158:022696
PEI¡OD oP ¡lc. . 1967-75
ttr¡ PEtr YtlR
1969 62.5 t9t0
1913 6¡. t t974
¡3.9 COE'. Ot SÍll -
PETi
84. I
50. 6
1. ¡687
¡f,¡.¡GttEo I tÎ ¡lIRl
l¡P REllEExcE r158:25577lt
PE¡IoD oP aEc, . 1968-76
tEtB Ptlf ll¡R PEltr
1970 25.20 1971 ¡7. ¡0
197¡ 29.60 1975 39.30
11.25 COEP. O! sÍtl. 0.lt6t
5r1l 15008
ctrctlltll rREÀ, sQ fl llg¡
IolBt¡ oP t¡f0tl, PEr[s . 28
IDIR PETi IEII PEII
t9{9 3t.8 t950 19.t
1953 3a,2 195tr 26.0
1957 27.3 r9s8 58,5
r96t 21,0 1962 ¡7.9
1965 63.8 t966 ¡9.0
1969 3C.9 1970 60,9
197! 26.8 19?¡ 36.¡
ñEtl r ¡r.6 SrD, DEt. ..
slrt
r5¡1?
RlrGIlÀ¡f,I ¡ lt tot¡tlt¡
itP tarBBatct
PII¡OD OF REC.
?tlR Pttñ
1951 2r.6
1955 26.8
1959 ¡9.8
1963 3?.5
196? t2r. I
19?t ¡6.5
t975 36.8
¡ tl6: ll!51¡a
. t9l!F76
tllt PItr
1952 ¡9.O
1956 a2.7
t960 29.9
196¡ rO.0
1968 15.6
1912 36.7
r9t6 56.2
20.2 colP. oF srBl. 2.6gla
¡oTts:
l, ÎÍE tq67 TLOOD PEIK r¡s rE! FESULÎ Or CICIO¡E DItl[ ltD
rls TtrBx Às llrF Ltnctsr r¡ î88 pERIoD 19¡0-77.
8[rGIlÀIfI B tî 1r ttto
c¡tclllr? lrll, sg ¡! 89.8
lu¡lll Ot rllull. Pllf3 . 9
ftll Pllr rllt PtlÍ
1968 38r t969 28r
1972 329 1913 15'l
1976 255
Ittf ¡ ?Sa sTD. Dlt. .
rrrr 298 18
tm? R tÎ Í¡r10Ítt
ilP lE?ltgrcl . 1t61r71630?
gIllOD ot ¡lC, . t9ó0-7ó
llln Prtr tät Pt¡[
't9t0 19t r9tt 327
197¡¡ 20r 't975 171
8l COll. ol sfEl ! 0,2¡¡l
H011 R l? ttlctttltt
cllc¡illT rIEt, sQ ll = 2091 ltP EEPEREICE = l7?:2aâ153
¡ltltllR ot ÀIfolL PE¡Ís ! t6 PEsroD oF lEc. . l95t-66
llt¡ PErfr fErR PEIß rDrn Þtrk ttl¡ Dtlt
t95t 309 1952 t9t 1953 33 I 195¡ tt9
1955 t89 1q56 212 1931 370 r95t 3t9
t959 219 1960 t9t 196t 235 1962 37t
1963 190 196¡ 272 1q65 595 19ó6 2t;
Ilrl . 293 SîD. DEl. . tl1 Co!t, or slEs - 1.62¡2
torBs:
l. TÍE 19tq pLOOD pttr op 784 CUiBcs rts Ttfli rs T8r
IIFC'ST tX |!|llB D?RloD 1925-66.
2. T[tS S1¡lrol fls tot rsED Ir TRt 8lcrotÀL rtrLtsls,
BECÀûS! TEERE tnF SIGirPfCtIl ptRrs o? THp crîc[;?tÎ
III BOTII IEÌ: BIT OP PLT¡ÎY IID XOBfB :SLIFD EIST COAS'
RFGIOilc, ttlD !H!: lBEilD rX Tfi! pROSrBtllûy pLoT ¡,lt
lx-EETrEEr TÍOS! PoR ÎñE lfo B'GIOIS.
cllctlltr rlll¡ 30 ri - 027 irP nErlnlrcl t r1ól!52r¡40
l0llll ol ¡ltttll PtIIS ! 6 PB¡¡oD 0? ¡Ec. . l97t-76 slr! 33307
¡llctiol R rr f,EtfrÍllBts
t¡lt Ptlr rlt¡ Pl¡f IEf,f P?l[ rttt Pf,IT
19?t t26 1972 636 197! 329 r97¡ 837
19t5 39r r9t6 636
Crlclllll rllr' S0 ñl - 81.3 llP nl?zRt¡cE - I1l2:0899q0
f0lllt ot lfr0rl PEtrs . 1l PERIOD 0t REC, . 1960-10
rl¡l . lto 51n. Dll. . t3¡ Cott. Ol Sfll - 0.6212 IEI¡ PEÀß I'I¡ PEII YI¡R PIÀi IETR PBTT
tolrl:
1960 ¡6.7 t961 ) 97.5 1962 32,a 1963 2a.2
1. ltt t9¡t ?L(þD Dl¡f ot 1237 cortcs rts llrtr ¡s Ρt l96t ?1.8 t965' t¡2.8' t966 5T.8 196? 69. B
l'llelst It ttr P¡¡loD 19¡0-77. ûrrlrR RnLE fo, I orlt 196t ¡r.9 1969 :16.6 r9t0 21.3
ttrg Dt¡¡ ?o¡ tE¡s sÎll ll3 oslD li lFr BEGrollL Prol. il¡t - 09.7 STD. I'EY. . 22.2 coll, oP SFES É 1.0221
98
Water & soil technical publication no. 20 (1982)

sllt 333 2[ i¡[e¡TEPOPO I It rElEltfir 3. ÍIOßTH IsI¡ITD tr¡sT COAST DATA
CÀtCEtElT rBEr, SQ fl = 31
llliBER OF tffttll PEtfS r I
I8¡8 PETf, TE¡R PEIf,
1960 ¡9.79 1961 8{.9q
t96¡ 35.42 r965 29.79
il¡t = ¡1.56 s?D. DEv. =
srlr 33307
itP BEIERltcD = I1122062921
PEBIoD cF FEC. - 1960-67 t54 t0
IETB PE¡Í IBTR PPTI(
1962 21.25 r 963 1 6.50
1966 42.84 1967 51.97
21.63 coPF, OF srEt = 1.0182
¡IIGÀIUT R IT TB POAERE
crfcEiEfT rntt, sQ rt = 28,2 lltÞ SElBlE¡CE - ¡112:087904
l¡tlDlr ol rlfûrl PEÀÍS = 1n PBBIOD oP REC. . t967-?6
rlt¡ PEtr
PEIK
IBIR PEIÍ
1967 5A,O2 'EIR 1968 31.53 1969 26.20 t9?0 11.20
1 971 r0. ¡9 1912 16.01 19?3 r¡9.39 1974 1R-22
t 975 21.6t 1916 29.69
lEtl . 30.86 SrD. DEY. = 14.33 coEP. oP slEr = 0.8759
tE^n PEtß
srtr 43112
clTcFrgtT tBlt, s0 rr = 228 ItP REtEnE¡cl . f,85:r101680
folBl8 Ot ll!ûÀL PEltrs = 16 PEnIoD oP RBc, = l'161-76
rtlt PEtr tElR pElf, IETR PBIX TEIR PBIf IETR
196r t6.2 1962 36.5 1961 11.4 t964 12. 1 I 967
1965 33.5 1966 19.9 1967 1 1,2 1968 17.1 197 t
t9ó9 19.1 1970 L2.7 191 t 21,9 1972 11.2 197 5
t9?3 17.O 1974 26.2 1915 lq.3 1976 15. 6
¡Etf{ =
15.2 CoEF, OF sRE¡ = 2.1165
llll = 2¡.8 sfD. DEv. =
rotts:
1. TEB 1967 PLOOD PPÀr 9ÀS rFE RESÛ¡,Î 0P CICLO¡E DrlÀft À¡D
tÀs Tl[ut Às ?EE LtacEsr rx rtE PEBToD 1940-77.
q48
tl
CIlcllllE¡T lnsl¿ SQ Il =
X0lBß8 OP ltltrlL PBIÍS =
IETR PEI( fE¡R
1953 67.3 195C
1957 r¡9.7 1959
1961 27,t 1962
1965 33C.0 1sC,6
1969 59.7 1970
1973 54.1 19"4
1977 5?.0
IrrorrPr R rr REPoBoÀ srtE 15¡32
srrE t0¡34 19 POf,II¡ñEÙUT R TT PUKEÎIIROÀ
cllc8lltl lf,Er, sQ Ki =
ItlBES 0? ¡ftnÀL PEtÍs =
IEIi PEIß IB¡R PEàK
1951 20.0 t96s 62.3
t968 12.7 1969 11.9
1972 21.8 1973 18.3
1976 33.7
iB¡Í = 27.6 SID. DEV. =
srlE 1003428
--------ï-----
IIIS PBTÍ
1965 3¡.0 'EÀR 1956
1969 31.2 t970
1973 59.0 197tr
CÀTCFÉEII! TRET, SQ RII =
IUIBEF OP r¡fûrl. PE¡KS =
lltP RE¡zREIICE = ¡75:213145
PEEIoD oP REC. = 1964-76
fEÀR
19 66
1 970
19 74
PETf, fÈTA PBÀK
15,2 1967 41.6
24.6 l9?t 32.0
19,3 19?5 \0.7
14.4 COPP. oF sßE¡ = 1.1932
CllCSllrT lEll¡ SQ f{ll = 210 lltP FEPPREIICE = n85:54t802
¡0!BER Ol Àltûrl PEIÍS = 12 PERIoD 0F REc. = 1965-76
NOlES:
1. lHS 1958 FLOOD PE¡Í I'¡S 18E ITRGZST III lFE PI¡IOD
t870-1977. 11 ¡als EICLI'DED PROË TIE Àüf,LtSrS olDt¡
R0Lt ¡o.3. 8tt1 ¡ts rfcLttDED rr r¡B DE¡lvlrro¡ ol
r8E GEIIERILISED COFYE PCR 188 TREA,
2. TRE 1964 FLOOD PEIK tts PROBIELI 1f,8 SECOID LlSCtS? fl
üE¡OR!. IT ¡ÀS lttElr ÀS lnt SECOID LTRGEST l¡Oi 1905
(¡flB[ TBE rtfE RFCORDES ¡ÀS TITSTILLED) TO 1977
If,CLT'SIYE.
53¡
25
¡EIRIrtiI I rr cllt:tl
tlP BETBRI¡C! Ê 186:191C23
PEnIoD 0F RBc. - 195Þt?
PEIÍ TE¡R PEItr ÍITR
64.9 1955 52.6 1936 'III 79.6
211.1 1959 ?r.9 1960 5?.t
113.2 1963 64.8 t96a t33.0
183.1 1961 310.{ 1968 t3t.?
306.9 t97t 1t7.3 1972 66.3
.8ß.4 1975 65.1 .r9t6 tt6.0
ËEt[ s 120.5 STD. DÊy. . 90.9 COEp. Ot S¡!¡ - 1.!rt8
¡rrG¡r¡I¡I I ¡1 ¡ODûlt¡I
CtrcllEf,T lREr. sQ Kll = 2318 irP altl8Efct . a862222A22
NUIBEn oP lf¡ûÀL PEÀI(S = 10 PERIOD 0t lzc. r t96?-?6
PEI (
498
325
147
260
tEtF PSIX
1968 185
1972 112
1976 339
SÎD. DEÎ, =
CÀTctrlllll¡ ÀlEt¡ SQ Kll =
IIU;8ER OP ÀT¡OT.L PEIKS =
I ETR PIIK TDTS
jt
951 262 1952
1 955 272 1 956
1959 283 1q60
1963 1111 1964
1967 !c9 1968
1971 3F6 191?
1 975 450
ctlcBl!|Î ÀRErr sQ Il . 207
llllDll O? tlto¡L P¡lf,S E I
ttl¡ PEIR ttlB PEtr
1969 327 1970 385
1973 62 1970 rs5
illl - 218 STD. DBY. =
YEIR PElf rtlR tt¡l
1969 9t 1970 t95
1913 117 19t¡ 212
148 coEl. oP sflÍ = 0.7157
:11ïl-:_l:_::*:l_1:::
l¡rl0 lÀP nEFEnElcE - ¡?8:17¡076
25 PERIoD oP FEc. = r95t-75
PEÀT IEÀR
219 1953
258 r95?
136 196t
616 1965
289 t969
1tt7 19?3
PETK PII¡
1 rto 'ETN t95¡ 2¡0
160 1958 tt7
3?C 1962 2t2
19c 't 966 76a
"?0
t970 t93
2c¡ t9?4 t2â
TT8O8AÀTTRÀ F TT OEÀXfTRI R'ì IEII = ?Bt STD. DEV. = 234 coEF. oP sflB = 1,50t2
PEII YEIR PFAI( IBII
17.9 1961 F2.5 1968
42.9 19"1 28,C 191?_
ò8.6 1915 30.8 1976
PEIf
35. 0
47. c
54.1
iEIl = q4.9 STD. DAg. = 15. 1 CoEF. oP sXEí '= 1.4881
srrB 1C4345C TOIGIRIRo I l? ltttltcl
112
2C
lilP ¡ElERPfCr . it02:30000¡
PERToD oP REc. = 1937-76
Pll¡
280
1225
3t5
r20
J27
IEIR PEIK ?BTR PEÀf, ÎETR PEIÍ I'I¡
1957 2tt' 1958 1915 1959 245 1960
1961 270 1962 345 1963 300 t96¡
1965 54C 1966 r¡',t0 1967 826 1968
1969 110 1970 457 1971 188 1972
f973 230 1974 386 1975 :113 1976
;BÀII = 497 sTD, DEv. . r¡07 CoEF. oP SklÍ . 2.735a
srlE 1043460 loHclnrEo F rr Pûfll¡lltl
SITI
155tq
8lIÀf,tTtÍE I t1 8ñtr¡?tIF
C¡lClü811 lll¡r S0 Kll = 1557 llÀP nEF¿nEilCE =
¡ltllgl O? ll¡t f,I. PEIKS = 20 PERIOD C! nEc, =
flt¡
I 957
1961
I 965
1 969
197:t
ll78:43619¡¡
't9 5t-76
ÞETf IE¡8 PEAI YEÀR PB IR tElR PStü
638 1958 1166 1959 367 r96C 657
27t 1962 8',r6 1963 r¡90 1964 2110
22\O 1 966 550 1967 r 711 1968 520
620 19t0 2C6A 197t 1 289 1912 642
350 197tt 580 1975 1t5 19?6 7¡0
lEtl = 9¡3 SÎD. DDV. - 639 coEF. oF skrc = 1.2069
sltt 15536
¡¡I;ltrt I tT oGILtIts EnIDca
rlP REFBREIICE = i8?:55r818'
PEIÍOD 0P REC, = 1969-16
PEÀT tIÀR PETR
'BÀI 1971 196 1972 142
r9?5 187 1976 251
101 COEF. OF SKE9 = 0.334¡
CtTCSllE¡î ìRBt, SQ Íll ll95 ttP BgFERBTCE - 1112:31i1910
IUTBPA oP Àxtfttl. PEIßS = 11 PERIoD oP REc. á 1960-t6
YEIR PE¡f
PE¡i IEÀR PTTf, ttl¡ Elll
1960 212 'EIR t96l 181 1962 2g I 1963 21'
t 96{ 869 1965 619 1966 302 1961 ?09
1968 261 196q 272 1970 370 1t71 2a9
1972 3C6 1973 192 1914 3 19 tt?s 260
1976 360
lltf = 353 STD. DE!, - 19q coEP. o? sßlr ' 1.7tlg
lrofES !
r. ÎÍE 196¡ PLOOD PEIÍ f¡S îtßEr lS SECO|D Lrloltt ll lll
p?Rron 1905-77 (SEE tOlPS POR Srft l0r¡3t59t.
CllGllllr llllr SQ ftl =
lûllll ot llt¡llL PEIrS =
ttll Ptrtr tttR
t95t 1068 1959
t9n2 800 1961
1956 555 1961
1970 r î57 r97r
t97l . 660 1975
PEII
256
475
2058
705
617
llll - 920 SrD. DEl. .
6q0 t9
lÀlOERl R tT GoRCE C¡rBLBllr
ItP BtPlFEllcB f?8:7 37921
PERIOD oP RBc. = 1958-t6
tPÀR PETÍ IETR PSIK
1 960 6\2 196't 209
1964 217A 1965 t0t5
1968 5?6 1969 tr26
1972 8r¡3 r9r3 342
1976 920
529 COPP. OF S¡Er = 1.6132
Water & soil technical publication no. 20 (1982)
99

ïI-'_____ ::19:
lt¡IPt0r n À1 i¡¡lÍt¡lrt BF 4. CENTRAL HAWKE'S BAY DATA
c¡lClllll t¡ll, S0 rl =
totll¡ Ol lllotl' Pllfs .
1580 itP sEPlaExcr t89:268623
15 PERIoD oP REc. = 1960-7q
PEItr IEII PETÍ
1750 1963 568
976 196? 11tt
r 1t5 r97t r4¡5
517
llr¡ PElt ttrn PEr( rEtn
1960 28s0 1961 tqts ß62
t96t 550 1965 1820 1966
t968 1100 t969 qt6 l97o
1972 998 1973 t239 197tt
llÀt . 1167 slD. DEv. = 6ql COEF. ot sf,E¡ = 1.2631
¡otts:
l. tt! 1876 ¡tD t9¡8 TLOOD pEtÍs OF 3058 trD 3172 C0iECS,
¡lsPtctltl¿t.rERz ltftf ls lEp 1¡O LlncESr pBtÍs
¡¡ TÍB Pr¡IOD't876-19?7.
SITE
23001
cÀÎc8íEIT tREr, S0 Ktt = 193
lluãBEF OP t¡¡UÀL PETKS = I
IETR PETK fETs PE¡T
1969 n5 1970 298
1973 365 1914 f q I
T0lrBÍ0RI R tÎ ÞrftllPo
llP ¡ETERE;CE . t134:21t367
PEAIOD 0P RBc. = 1969-76
YEÀ8 PU ÀÍ
1971 805
19?5 771
IETR PETÍ
1912 250
1976 811
ItEÀtl = 47 2 STfi. f)Ey, = ?87 coEF. oP srEr = 0.2559
sIll
C¡qcllBft llEl¡ S0 il = 18t
IOltlS or ll¡orl PE¡rS = 12
trl¡ Ptt[ tE¡a PElr(
r955 r9!.29 t966 117.60
1969 95.33 r9?0 rq2.09
1973 1t2.71 r97[ 175.73
rlrt = 'l¡¡.01 STD. DE9. -
r8¡REEOPII R ¡T ÑfLLTR¡EI
llP REFEnEßCE = i97:061529
PARIOD 3P REC. - f965-76
YEAR PET(
I 967 127 . 10
1971 1¡1. c2
1975 t¡3. 1 1
tEta PEti
1968 142,4t
1912 90.38
1976 226.20
38.79 COEF. OF SkEg = 0.7724
SIlE ?3C02 lOT¡EXÛRT I TT REDCLII?E
cllcBlEìtT AnEÀ, S0 fl - 826.1 Ëtp RE?ERElcE ¡t3¡t:255320
ttlBER oP tùtûf,L PETIS = 3t PERIOD f,p FEC, .t92¡-65
=
srtt
t9711
C¡lClllfT tlBr' S0 Íl = 171
lúiDtR Ol tllltll PtlÍS =
IETI PETT TETR PB¡R
1965 335.?? 1966 138.51
1959 103.64 19r0 336.01
l97t tq8.62 1974 4e.22
Í¡IiGIROIIII R TT lBRRTCF
ËÀP aEPEBEICE 'tt [89:325746
PERIoD oF nEc. = 1965-75
IEIB PE¡T IETR PETtr
1967 97. 00 196A 221 .9?.
1971 285.61 1912 125.91
t975 I 9.09
lll¡ - 169.85 STD. DEg. . 1t0.92 COEP. ôp sßF¡ = O.¡q76
218 íì I iontxÀ R tÎ nloPûfel
C¡lCHllBlll tREt, S0 KË = 237î ðtp nEFEFEXCE = ¡tt5:5¡t2895
NCüBnP oF llrutL PEAÍS = 19 pERtoD op FEc. = t95g-?6
YETR PXÀX I?IF PEÀK IETR PEAR IEIR P'Ti
195S 926 1959 ?16 1960 1229 t961 36ß
1ç62 q35 t963 495 1964 450 1965 120
1966 l1¡5 t967 14t9 1968 768 t969 ¡03
1 970 6 t0 1911 163 1972 {01 1973 920
1974 t 397 t9?5 4tO 1916 t¡48
ItEl¡ È 818 STD. Dgs. = 167 coEP. oP sxEr . 0.¡t701
TOTES:
l rBB t93A FLOOD pFÀK rts FS?rrtî8D rT 5371 C0'DCS. r1 t¡s
FICLTIDFD pROt lFp ¡tatLtsrs 0¡tDER Rtt¿E to.3, r;D ?BOtl lir
DERIfIIIOII O! IIIP GEf,E¡II,IsED CITRYE POR T8E T¡lI.
:l:_"______3ll 9:
TIOHTßI E ÀT GLE'?ILLS
cÀîcEÍEIÎ r¡Pr, S0 iñ = 9q7 ñtP nEPEREI¡CB 1114:072775
lUlBFn oP Àf,IûIL PE^¡S = t3 PERIoD oP REC. = 1961-76
PFIK IEI R PEÀT IEIR PPIX lErl Pl¡f
q03 t96 5 tút2 1966 511 1967 6a2
tc0 t 969 t3c 1970 62A 1971 290
tF7 1 971 316 197¡1 606 1975 290
q 34
I ¡t8
1 96¡
t96B
1912
1976
ItBt i =
05 9
22s02
crScHÍEiÎ rREt, s0 Rt -
LûlBF8 oF ttfutl PEtfS =
rEta PEIX t?t¡ Prtß
sTD. DA9. 240 COEr, Or SkBt - 0.7261
25tt
1l
BSr R lr srlPutel trIDet
FIP EE'ERBICB z t124.241523
PE¡iOD oP REc. = t96t-?6
rBrn PErÍ ttlR Pllf
1966 125.21 r967 213.5t
r970 126. 30 1971 372.06
r974 rt99.98 1975 91.72
't96¡r 27.Ctt 1965 2¡2. ¡6
r968 528.90 1969 31. tq
1912 q2. ?1 1973 1?0, ¡8
1976 281.30
lEtl = 215.63 sTD, DEr. E 164.90 cOtF. op sxrr E 0.06t6
IOIES:
l. lEt 1938 pL(þD pEt( ¡ls tSTrñtlED 10 BE tr Erclss o!
1931 Ctrttcs. Iî 9¡s lxcLoDlD FBO! TßÌ tttltsrs ûtD!¡
altlE fo.3, ttD ptot tÍB flERrttTror op tfp GBIEBILTSID
contE ?ot rllP ¡REl.
üEtI = 614 SÎD. DEV.

slrt 2¡201
lOf,ITO(T R IT 8ED BRIDGE
ioîûtRt F IT tooDsfocr(
CllcÍlltr rBll¡ SQ Il =
lúlBg¡ Ot rl!ûll. Pll¡s =
tt¡t Pttf tE¡B PEIÍ
1923 l\12 1924 1727
1927 2265 1928 t 161
1912 1tt12 1933 1172
1936 2548 1937 I 161
19¡7 931 19118 1897
1951 þ3q 1952 1076
'1955 1\12 1956 2237
't960 1019 1961 1359
195{ !l¡ 1965 1557
1969 333 1910 1090
r9t3 626 1911 2500
iBll = 1380 sTD. DEv. '
srlE 5690 1
cÀlcfillEllT tREl, S0 fr =
IIÛ;BER OP ¡XÍI'ÀL PEÀKS =
IEÀN PEÀK YEIN
1967 19 1 958
197f ttl 1912
1975 s3 1976
59 SrD. DEY. '
2380 q¡
rÀP !E!EnZÍCE = Ít30:338119
PEBIoD 3F PEc. = 1921-16
IEIR PETT IETR PBIÍ
1925 1112 1926 2432.
1929 291f 1931 178ü
193rt 1133 1935 198?
't 9 38 2e13 19q4 8q9
19q9 2898 19511 2690
1953 1115 t95r¡ 1q16
1957 1218 1959 1415
1962 764 1963 't472
1966 1tt1 1968 1695
1971 2243 1972 5A2
1915 1 585 1916 1244
837 cOEr. oP SIE¡ = 0.ltlll5
tolEs:
t. tttotl Ptl(s mR TEE BLICi BRTDGE SÍTE([O.232i{21 íERR
nsED POA Î[E lEl85 1923-60.
2. TEt rlfûll FLOOD Pgrf,S POR 18S lEtns 1939-46(EXCLllDrllG
191¡{l rtD 1958 ¡EBE f,to¡r rO BE LBSS T¡lt¡ 283 C0iECS
(1OO0O CUSBCS¡ rrD 'EFE
rSSBIED rO BE 255 C0iECS (9000
c[srcsl. TIESE PBlfs IERE 0sED rf, T8E FRBogBrCt tl{lLYSrS
POB lRE SiTE BI'T ¡OT III lII' BEGIOIIII ÞLOT.
3. fo tirûll PEtßs ¡lRE lrtILIBLE FoR 1930 tfD 1967.
t. TRS 1917 PLOOD PPtf, OF 3964 CUüACS lls TÀf,EÙ lS lRE
LIBGBSÎ fr rñE PERTOD 1868-1976.
srlE
232Cq
OTÀI¡E I Iî GLE'DOT
c^TcftiSl¡T AREÀ,5Q (ü = 24.3 ürP nEPEFEÍCE . [141:015921
Nlt;BER OP ÀilUnÀL PEAKS = 12 PEaIOD 0P ¡EC. = 1965-76
YEAR
1 965
1 969
1 973
¡Etil = 1ñ.51 slD.0!Y. =
SrrE
PEÀT YEI R PEÀK ÍFTR PETß
1.19 1966 15.0C 1961 6.89
4. 11 1970 \.51 1971 16.5c
7,86 1974 37,31 1975 7.06
2321î
IEIS PP¡K IEIR PEÀI(
1966 43. t1 1967 r¡1.57
1970 14.75 1911 95.53
1974 115.40 19?5 24.88
ItEtX = 48.71 STD. DEV. =
IEIR PETI
1968 9.68
1972 1.53
1916 8,32
9.qq CoEP. oF srE¡ - 2.3603
crTcfiiEìT ÀREt, 5Q KË 5q.{ rÀP BETEnENCB
llUlBER 0P t¡|flûÀL PEIKs = 1C PEaroD ot REc.
YEÀR PTiÀK
1968 55.83
1912 r9.87
5. SOUTH ISLAND WEST COAST DATA
srrE
s2916
CÀlCfltlEllT IREt, s0 Kl = 5C.8
X0iBEF 0P ÀtlNoÀL PEIKS =
B
IEIN PEÀK ÍEIR PETK
1969 61.7 1970 B3.q
1911 110. 1 1974 15e.0
oËIKERE r lT POSDlf,t
= 1106:'l¡1751
= 1966-75
IEAR P'IR
1969 31.8t
t9?3 t¡.55
t2.71 coEP. OP SKES - 1.2578
coBE B lî TSILOtrlE
lllP REFEREIICE = St3:020¡82
PERÎoD oP R?c. = 196976
reÀR Pfrx IEIE PEIÍ
1911 98.0 1972 94.3
1975 142,5 1976 131. 5
lEÀX = 110.1 SÎD, DEV. = 32. q CoAP, oF SßB¡ = 0. l3lt
ËDt¡
sri¿
s7009
ctTcHl:IT À88À, SQ Kll =
llUltBEn oP ¡.ù[0ÀL PFÀxS =
P EÀÍ
6tt
46
74
ÌETF PEÀK YEIP PEIT
1968 r¡13 t96q 255
1972 392 19?3 112
1976 163
ËBrI =
345 5T¡. D¿V. =
t¡8
tc
163
FrcrKt R lT toss BosB
ItAP REEFRPIIçE = S13:307569
PEnroD oF PBc. = 1961-76
YEAR PEAR
1969 60
1913 19
fttR PEli
1970 6¡
t9?¡ 4¡
21 coEP. oF sFEc = -0.3054
IIOTODKI R If GORGB
irP REF F¡:{CE = 526:288863
PERIoD 0F BEc. = 1968-?6
YEÀR PDÀT ÍEIR PITÍ
1910 16C 1971 ?00
1a"4 95? 1915 233
176 coEF. oP sKE¡ . 1.1262
IOTES :
1. TTIIS STITTOÙIS PSOBÀBiLIFY PLOT DTD ilOT COTFORII 1O TÍE
SOUTH ISLÀND IEST COÀST REGIONÀL ?RPIID. I1 ÍAS O'TITID
PFO| lHE DtRMÎlO¡¡ O? ?UE nEsIOIIL CT RVP lllD lls usaD
INSTFÀD IO IiJEPTil' À ¡IELSON Sf'B-FFGIOI{.
Crlc¡lttr lRElr sQ Kll =
totBt8 0? l¡Í0ll, PEtrs =
t¿t¡ PEtf tttn PEÀr
1969 145 1970 ?99
1973 1054 197t¡ 1 600
lE¡l = l01B sTD. D!Y. =
Srll 57101
17 50
I
CllCElltT ÀRErr SQ Il = 60.7
|UIIBEE OF lt¡lrÀL PEIÍS = l0
PETtr IETB PEÀT
ttl¡
1967
t 971
1 975
96 1968 95
39 1972 toq
29 1976 153
llAP REPEF¡ilcF = s13:21232C
PERIoD 0P REc. = 1969-76
1EÀR
r971
1915
PETK f?Tß PEAI(
?83 1972 1223
n81 1976 1062
288 COEF, 0P Sf,Bt = 1.2661
IOOÎE¡E N ÀT OLD HOÍISE ND.
ilP BEPER!¡CB = s1l¡:37?347
PBRIOD oF RPc. = 196?-76
IE¡R PEÀX YEIR PEIT
1969 9 1970 5.3
1973 5 19711 18
llll ' 68 SID. DEV. = ¡ú6 COEF, oP s[El = 0.2¡45
toîts:
1. r Dri ¡rs cotstRttcTBD oPslnBti oP ÎÍE sTrrrot r[ 1973
801 I1 IS COtS¡DlBtD 10 ntVE FO SrCIrPrC¡ìfr EPFlCl
ol lEB ttrtrt¡' FLooD PEtÍs.
2. IEIS StttloÍis PB0BIBlLIlt PL01 DID lfol ColPoRli 10 Tñt
so018 lsllft ¡Esr eolsT SEcforfÀL TBBnÞ. r! cls o;rTlED
?RO' lEI DEBI'IIIOII OP ÎñE REGIO¡¡L CIIRY9 À[D ¡¡S ÛS?D
I¡SIETD 1O DB?T¡T ¡ IELSOII SOB-REGIOII.
3It! 51502
I'ÀIROI R AT GOBGE
cllctrEr? ltEr¡ sQ rr = ¡6¡¡ ilP SEtERE¡cE S20:¡93149
tl¡tBll Ot lll0¡L PPÀf,s = t5 PERIOD oP REc. = 1962-16
ttr¡ PEIf, rElt PEII IETR PEÀF IUIR PEI¡
195 2 879 1 963 7527 1954 1016 1965 ¡¡t5
I 966 7t3 1961 t002 1968 1 102 1969 720
1970 86t 1971 l¡46 1912 1003 1973 316
197¡ ?00 1975 887 1916 852
llll -
302 COEP. OP SÍEr = 0.2891
srlt
â33 sfD. DEg. =
601 l lt
cltcf,ttlt tREl, sQ K; =
¡ÀIRTO R À1 DIP PLT'
505 iÀP BBFEFE¡CE = S33:29054t
t¡tlltB Ol ¡¡ltll' PE¡f,S = 25 PERfoD 0F REc. = 1952-76
IE¡¡ PET( IEI R PEÀ[ ÍETR PEItr tEtn PrÀK
1952 12,{ 1 953 223 1954 211 1955 320
t956 16S I 957 ¡30 195S 273 1959 280
.t
1 960 60 196',r 270 1962 305 1963 116
I 96¡ 262 1965 190 1966 ',l8f 1967 244
1968 30q 196 9 202 19a0 309 1911 231
1972 237 I 973 248 1914 348 19?5 451
1976 249
llll "
sltt
260 STD. DEV.
'
601 16
CrÎCEtlll rlll¡ SQ f,l =
¡tllll ol rttoll PllRs =
tEl¡ PBt¡ fttÊ
t966 43
1970 62
197¡ 59
illl = 61
rotts:
PEIß
192
11
78 COEP, oF srEI = 0.7396
ctrRlû R lT ltELLs GllÊ
ItP REPERFTCT = s¡0:26535?
PeBIoD 0F REc. = 1966-76
YEIR
f968
1912
1916
sTD. DEV. = ¡EtX = 5tt 9
121 cOE¡. ot sfiE¡ = 0.6130
PEÀ( fEIN PETß
1967 5l
65 1969 {c
'191 1 51
51 1 973 43
1975 100
88
sTD. DEV. = l8 CoBF. OP Sf,Ec = 1.3649
1, 18' I97$ PETT ¡IS TTf,E¡ àS ÎIIE LIRGgST TN ¡88 PERIOD
1951-76.
sltl 15276 sgolovEn R tT Borxlrs PElx
crtcEtlrr t¡lÀ, s0 fü
ioiElE E
OF llfltlt. PElf,s =
10 8S
I
l!ÀP REPEREùCr = S132!589786
PEnIoD oP REc. = tc68-75
tElB PBIÍ IE¡R PETK YETE PBIÍ fEÀR PTÀX
I 968 569.7 t969 60q.0 1970 371.0 1911 291.4
1972 39¡.0 l97l 210.0 19?4 rt58.5 r9?5 508. n
Ittl = q3¡.8 SrD. DEY. = 121.8 CoFF. or s(Bc = 0.039C
S IIE B4f0t
CLEDDTO P 11 fIILIORI)
CtTcStlEllT ¡REÀ, sQ Xr =
ÍUIIBEF OT INIÛIL PEÀKS =
155 tllP RflFEFEllcE = Sr13:908106
11 PE¡IOD OF REC. = 1965-?5
lulR PPA K YEÀR PEIK YEAR PEIf, YEIR PEÂf,
1966 422 1967 1\7
1 965 u23
1958 400
t969 5q0 197C 512 19?r 572 1912 533
197 3 52U 1974 675 19?5 461
Water & soil technical publication no. 20 (1982)
t0l

9100r
GNE? R ¡T DOBSO| s¡18 93207
IXÀllclllltt n ÀT Bl.Àcrs Potli
CllctiEll rREl, SO Xtl - 3830 llÀP RE'EFEIICE :
¡ûllln
crlcñiltr rlEl, S0 [ü 23q I'tÀP
oF lI¡[lL pFÀf,S
S¡¡:8tOO?7
REPFnE[cE s38:340281
= 9 PERIOD 0P RBc. - t96O-?6 lolEER oP tlitÀL ÞEtÍs = 11 PBRIoD oF FEc. = 1965-?5
IEIR PETT IEIE PEÀK tElR
t968
PrtÍ
36s0
tElR IEI¡ PP¡I P8If, fEÀR PPTi
PEÃr
1969 qr13
Pr¡f
1965 272 'E¡8 1966 290 1967 428 'ETR 1968 q34
1972 lt0s0
r9?0 q800 t971 233S
t9?3 3935 1974 1969 579 1970 412 .t9?1
1976
3695 1975 aO38
338
33S0
1912 l8?
1973 498 1974 975 19?5 534
iEtt . 37?8 STD. DFv. = 669 coSP. op SÍEt = -.1.02f7 lB¡l = 073 SID. DEV. = 193 cogp. OF Sl(Et = i.BBrtF
xolEs:
l. TFE iql6 pEil( totts:
or 6660 cuüEcs frs ÎtÍEf ts TnE
rr
Ltnclsr 1. TEE 19?4
TIF
PEIÍ fÀS T¡IEII IS TilB
PE8IOD LrrCESl If
1900-76.
lNE ÞEFIOT)
1
2. TIE lq40 pErx
887- 1976 .
oF 5300 CÛrlECS ¡tS Ρttl¡ Às lEE rErBD
LTPGSSI TT TÍE ST'E PESIOD.
srlB 93209
iIßOIA R TT PILLS
s¡ 1? I 140?
lll:: l_:_11-::::1
cllcflllT
cttCf,iEiT
rBBl, S0 [l . 980
l8rt,
irP RETEFEICE
sQ Kr l¡P
= S32:683596
?90 RE¿'nErcE S¡5:2Ot9Orl ¡otEBa o! tlfttll, PPtf,s
¡û;E?R OF tt¡otr. = 13 PERIoD o! REc.
PBIIS = PllIoD ' r96q-76
9 oP REC. = f96B-76
IEI¡
IIIS
P?IX
PBTß IEIB PPTÍ TEIR
IEIR
PETß fETR PETÍ
PBÀr
1968
YEÀR
1700
PEIÍ
PrT[ 196t g¡7 1965 277 1966 ¡6 r 1967 758
t969 1051
1972
1970 1260 'ETR t971 589 19ó8
lc2q
995 1969 808 1970 10r¡1
1973
1971 6¡?
t{09
t9t6 .r7¡
1974 1039 19?5 t3r6 1972 8¡¡ 1973 685 197¡ 836 1q75 855
1976 667
iEll = 1199 STD. D¡ìy. = 328 cosF. oP sÍpt - -O.aZS2 lgtl s 7¡8 sTD. DBt, - 207 CoE?. OP sf,EI = -0.9q91¡
toTts:
l. lrr t9q0 p,tìtÍ oF 2320 cullDcs cÀs ÎÀKEr ls rEE sBCOtD
L¡RC?ST rf ΡE PPRTOD rEtO_19?6.
srrt 932t1 Ë¡ftßITtÍt R tT ilnD LÀf,F
srTl 9320 l
B0LL!RRrlr!foÍr cllclltlT lttl, s0 fi = 857 irp RErtFtfcE s32:?4r6tl
llllBl¡ O? rfloll Pltfs E 13 PERIOD OP RSc. = 1964-?6
C¡lClllEXT tBEt, 5Q fl
635C ñÀP BEpERUItcE s3t:lAt629 III¡ PI¡f IEIB PEIT ÍEIR PETÍ YETR PETI(
¡oltlll OF ¡¡ù[tL PFIñS = tq PEBIOD O? RDc. =
196tr 843
1963-?5
t965 q48 1966 575 1967 7A1
1968 981 1969 518 1970 1655 1971 1095
IEI¡ PFTI( TET¡ PETK rEÀR PEIR rBlN PrIf 1972 1430 r9?3 818 1974 8Ê4 1975 ttt66
1963 {qol 1964 359C 1965 2150 t9ã6 t976 r 161
1950
1967 ogôC t968 5800 1969 4745 1970 E23O
t97t r¡7-

S ITE 91211 GLEIIROI R 11 ELICÍS
cÀTcfËr¡Î tRPt, 5Q Kll = 198 rlÀP REPBFE¡cE s39:?5335¡ ctlc¡tlll lllt¡ SQ r! '1980 i¡P REPERBICE s54:1r¡2602
llolBER oP tNllg¡.L PErf,S = PERIoD 0P REc. = 1967-77
Itllt¡ O? lllttll' Prlfs = l¡ PEBIoD 0P REc, = 1962-75
IIIR P:[ß YEIR PE¡X TBÀR PEIß TEIR PlIf tll¡ PEIÍ IET¡ PEIÍ IETR PEItr IE¡R PEIT
1961 159 1968 208 1969 1¡16 1970 t96
t962 855 1963 tt?tt 196q 10¡1 t965 633
1911 180 1972 183 1973 131 t9?|[ t¡5 l9ó6 771 !961 1300 1968 19q6 1969 661
1975 197 1976 178 1971 262
t970 1555 t97t 1073 1972 1423 1973 l1 19
I 9?r 1120 1975 1436
lEÀI = 18 1 srD. nEv. = 36 coEF. oP sÍ?¡ = 0.8ó08
lllf - lt5t sTD. DEf. . 365 coEP. oP sKEe = C.512?
tolls:
1. IIB 1968 PLOOD PEIÍ ¡TS lf,fEX IS TEÈ L¡FGFST II¡ îIIE
Pr¡roD 195?-75.
lt
stlt 61602 gÀIln-ÚÍt R 11 ttSBL¿ PT.
S IIE
¡lltÛ-0fft R tT itl.rlcs PÀss
6. SOUTH ISLAND EAST COAST DATA
SIlE 601 08 ¡lfRtn R 11 TtttttRrtÀ
C^lCFxEllT ÀREÀ, S0 Kü = 3431 llÀP REPÞFBI|CE = 522.253077
NúllBER 0P À[t¡UÀL PEIiS = 3¡l PPRIoD 0P RtC. = 193ó-t5
TEIR PEIK IEÀN PEII(
1 935 r 920 1 93? 1754
1940 1 100 1942 209tt
19ft5 125tt 1947 tq24
1 950 1 8?0 1 95 1 2494
1955 3q-1C 1956 20J7
1959 1213 ',1962 3qCC
1 965 1 030 1 966 1412
1969 2 380 1970 354a
1974 2830 1915 436C
¡ElI = 212" sTD. DEV. =
IOTES:
fETR P¡:¡Í ÍEIR PE¡I
t938 2011 t939 3396
19rt3 1330 19¡¡t 1510
1948 208n 1909 2010
1953 t613 t95¡ 3820
'1937 2201 1958 192q
1963 3000 196¡ t800
1967 3113 tq68 3000
1971 192C 1972 25AO
923 coF?. OP Srgr = 0.1919
1. STX ÀIINUIL PEItrS CTl8TN THE IBOVE SFPIES CERE T.PSS lEIi
1000 cuËEcs ìID SESE ÀssÛiED Âs 900 cil¡Ecs. TEE ¡sslttED
PEÀt( VAL0ES rERF 0SED r[ 1ñE FSEoUBICI tìrÀLySIS ?On TnE
STTE BI'T C¡FE ¡¡OT PLOTTFD TÌ DENIYTilG TNÈ RPGIO¡II
CIIRYE.
CAICItIIEII' ÀREÀ, S0 KF = ?t¡4,4
NÛIBEP oP ¡¡¡g¡¿ Pg¡¡5 = 16
fEÀR PEIK YE¡ F PEÀ¡(
t 96 1 250 1962 69-
t965 lt¡l 1966 525
1969 .144 197C 53:
1973 2C3 t97rr 139
ItEÀl¡ = 462 sT9. DEV, =
srlB 6 21 03
srlE 62105
CltC¡lltÎ l¡B¡, S0 ßÍ rl40
t¡¡¡BEl Ol rlIUrL PEIrS = 13
tBti Ptf,; rBlB Psrf
t96¡ 95 1965 126
t968 310 1969 52
1972 r5r 19?3 109
t975 20r¡
lElf = 187 STD. DZ9. =
cÀrfloPrr R tT cRllcloc¡t81
FAP RtÌPFnqùcE S28:99¡865
FERIoD oF RPc. = '1961-76
YEÀR PETK YETR
1q63 395 196¡
196a 707 1 968
1911 214 1q72
1975 8C? 1976
PEAK
3 3t¡
45q
432
531
2C.l colP. oF srEl = 0.2385
ÀcfiEROF n À1 CLtFr:ùCE
clrcñ;BlT tBEt, 50 f,t = 991 IÀP RE?ER!IIC!
54?: :119961
¡0tEzB Ol ll¡otL PEIIS = t8 PERIOD OP R¿C. = 1959-76
IETR PEIK tuÀR PEtÍ ÍEIA PEIK IEIE PEIF
t959 2AO 1960 202 1961 117 1952 236
1963 198 1964 22C 1965 171 1966 308
1967 378 1968 736 1969 321 1970 356
1971 361 1912 365 1973 201 197¡ ¡87
1975 199 1976 26i
lBtr = 33 3 sTD. DEg. = 182 coEP. oP sKEc = 1.5906
sr?r
6430 I
CLÀREIICP R IT JOLLTgS
flP REFEREIICE = s41=265862
PERIoD O! REC. = 19611-76
rEIR
1 966
1970
19?0
PEAK tEÀR PEIX
320 1961 121
150 1971 152
266 1915 166
91 COEP. OP sKE¡ = 0.4401
colr¡Àt R À1 ltfrÍDlLtt
CllCEil¡T lBlr¡ sQ fl ¡6r¡ ttP RBFERE¡cE s55:7166?7
l0lBll Ot ¡tl0rl PEIrS = lt PERIoD oP REc. = 1956-66
ttls Pllf, rElE PEtf YEIR ÞEÀÍ ÍBTB PE¡I(
t956 540 1937 355 1958 210 1959 720
t960 , 670 t96r ssc 1962 122 1963 1300
t96r 58 1965 580 1966 1000
ttll - 555 sTD. DPl. - 373 COEP. oP SIEI - 0.6019
tolts:
l- tEr 1923 rLooD PE¡f Ol 1700 C0IECS ¡ÀS Ttf,Er ¡s r¡B
Lr¡Glsl rr lFE PIIIOD 1A69-1971.
cllc¡lllT ¡¡lt, S0 f,l - 70.6 ltP REPEREÙCP = 540:018154
f0lllf Ot ItlOlL PEIf,S = 10 PIBIOD oP REC. = 1966-15
ITI¡ . PE¡f IE¡R PEIÍ YEÀR PEIß TEÀF PEAÍ
1966 66.5 196? 86.2 1960 11q.0 1969 66.9
t970 98.0 197 1 17 .6 1972 86.7 1973 82.0
t97¡ 93. ¡ 1915 123.7
llll = 89.3 sTD. DEv. = 18.9 CoEP. oF SßEf = 0.5772
slrr 6510¡ E0Rol¡ilr R l? itIDtËfts
Ctlcliltl Àßllr.S0 [Ë = 1070 ;lP BEFERE¡CB = 56l:932u62
l0lBll Ol llttll PEtfS = 19 PEIIoD CP REc. = 1957-75
ttlB Ptlr ItlR PETI IETA PEI¡ IETR PEÀÍ
t95t r1¡5 1958 562 1959 611 1960 r¡47
t96 1 559 1962 192 1963 665 196tr 465
t965 291 1966 241 1967 q60 t968 67|¡
1 969 2¡¡ 1970 858 1971 585 1972 83r
1 973 175 1974 5r1 1975 743
lElt = 500 srD. DE9. 253 COEP. oF sf,EI = 0.¡1991
S ITE
65107
crtcEllElIT ÀREAr SQ Kll = 3tt2
llUltBER oF À¡¡llllÀL PEIKS = 15
tETR PPTK YEì8 PEIK
1937 2t 2 1958 160
1961 ql 1C62 78
1 965 92 1966 56
1 969 12t 1 a7C 235
iErÍ = 138 SîD. DEY. =
SITE 66401
8ûRoFrr: R rT LÀrZ Sotttn
lltP SElEnBllCE = s53:6855¡9
PEBIoD 0F RBc. = 1957-71
ÍETR P'¡R PI¡i
1959 120 'B¡B 1960 122
19 63 1tt 196¡ 135
1961 163 t968 t8?
19?t 176
56 CoEF, OF SÍz¡ . 0.q875
¡Àr¡lxt8t8: F Àr oLD E.t,
cÀtcflllElT rREt, sO Kl 3210 iÀP BE?EREÍCE = 576:020?02
IolBER oP t¡iotl PEt[s = 46 PEBIoD 3P BBC. . 1930-75
PPIK IEIF PETÍ YEIR PEtf tEt¡ Pll[
'EIR 1 930 I 33 t 193 I 2039 1932 1303 1933 2209
1934 1501 1915 1303 1936 3112 1937 2209
1938 2t11 1939 l01q 1900 3738 t9tl 1612
19q2 1699 l9¡l 1076 t9q4 1 303 t9¡5 1¡¡¡
19¡6 1614 19117 2095 1948 1812 t9¡9 t359
1950 3C87 1951 2095 1952 1 218 1953 1303
1950 161¡t 1955 2322 1956 2209 1957 3993
1958 1044 1959 10q8 1960 1 388 t961 963
1962 tl.rr 1963 1214 t96rr 1416 1965 1232
t966 850 1967 2o5lt 1q6S 1Cl8 1969 ',1100
19?0 2501 1971 1190 1912 1676 t973 t000'
1974 1121 1975 1773
iEtl = 1694 sTD. DEY. = 709 coEP. o! SRB! = 1.5790
XOTES:
I. lSE 1957 PI,OOD PE¡Í fIS lTÍE¡ TS lNE LÀRGEST Tf lEB
PERTOD 1¡159-1977.
srlE 661102 rtlñÀf,tRtBr a tr 6('¡61
ctlcftEllT AREÀ, S0 rñ =
xurBER oP lIÍoÀL PEÀKS = 2C
rEIR PBÀÍ IT:TR PDÀf,
1953 1 3Cl 195q 1586
1957 42q7 1958 906
1961 934 1962 1303
1965 12tr6 1966 ll89
1969 16q2 lc?tl 26A5
iElI =
168? ST¡. DEv. =
2r¡ 6C
llP nEFEFEIICE 575:089775
PERIoD o? REc. = 1951-72
ÍEÀ8 PEI( TETB PIIf,
1955 2319 1956 2350
1959 1 557 1960 l¡¡r¡
1963 t303 196¡[ 195¡
1C67 2605 1968 1869
1911 1611 1972 2209
534 COEF. OF s(rl = 0.¡231
TOlES:
1. ?88 1c5? PLOOD PEÀK CrS TrKEh tS T8E ¡,tnGESf lr l¡E
PEnron tg69-1977.
Water & soil technical publication no. 20 (1982)
r03

6800 1
sBlrri R tT SrITEC¡,tttS 6Itt 696 r8 oPrñr I ÀBorE Roct¡ooD
Ctlclãlll ll9l¡ SQ [l -
lt itB¡ or tffoll PEtfs .
r ttt
196 t
t 965
| 969
I 97¡
l6¡ t6
i¡P ¡lrERlrcE 3 S7a:3t96t9
PE¡IoD 0F REc, = 196t-76
ÍETR PETi rB¡R PIIÍ
1963 r6r,8 1964 39.5
196? 66.0 1968 ¡8.3
197 I 3?. ¡ 1972 t73.0
1975 79.2 1976 6t. r
PTTT TETF PEIT
r84. 0 1962 37.6
t85,0 1966 12.C
1 r. ¡ 1970 58.8
52.1 197¡ 96.2
;Dtl " 85.11 StD. Dtt. 57.? CoEP. OF srEB - 0.891¡
ClTcÍiE¡1 lREtr SQ ill =
¡lllBEF ot t¡lotl PEIßs ¡
III¡ PPIÍ IDTR PP¡i
t96t t7t t968 9C
19tt 65 1972 167
19t5 ¡5
iEtl . lt8 StD, D¡:V. -
s ttg rt9t 02
tsFEoRlor SlE R tt iT. so;rns
RÀIcIltll R tBot! fLotDt¡r
CltcllllEl? tnsr. SO ft ' l¡cs itp ÀEppFBrcE
lüi0EB 59t:752290
oF tffott. pEtfs - l0 pEETOO oi n¡è. = ßG1_i6
?ttt Plrt tEtt PEt¡ YEIF P¿If
1967 tq29
IE¡R
t96S
DIIi
639 1969 tt15
t97t 3.tt
19?0 t599
1912 517 1973 1201
1975 t 159
r9t¡
1976 75¡
576
lEtl = 959 StD. DEr. = r¡29 CoEF. Op SrEt = 0. f253
toTls:
601 ¡ÀP RE!EnErCE . s8r:820{tt
9 PEnroD 0F FDc. = 1957-75
ÍEIR PFTI( 'EIR
PrI¡
1969 ?9 197A 204
19?-ì 5t tc?¡ 96
58 CoEP. OP St(El = 0.6t80
t. lrt tqSt ploon pttk op 1950 au;Ecs ets ltrEt rs T8!
L|RC!5T tf ?f,t PEFTOD 1936_?7.
cl?c[;Ex? lB!1, sQ fr ¡ ¡12 rrP nEtr8zfcE = Stct:5t2792
IttBtR o? tt¡[t[ PPr¡s : 41 PEIIoD CP ¡tC. - 1936-76
II¡R PETtr TEIR
't9¡6
PETÍ TEIR PEIÃ tE^R PEtf
t41 1937 62 1938 80 1939 33
1910 121 19¡l 126 1942 r03 1943 t19
19¡¡t 120 t9t5 663 1946 ¡3 r9¡7 33
t9r8 39 t9C9 50 1950 50 r95t 562
1952 200 1953 ó¡¡ 1954 69 1955 29
r95ó 69 1957 227 1958 1 19 1959 11
1960 t19 1961 466 1962 ?¡ 1963 28¡
t96¡ ¡0 t965 tt73 1966 t¡t 1967 10t
t968 15¡ 1969 65 t970 1 18 1971 92
1972 162 1973 39 1974 166 1975 t¡8
t976 61
ll¡l = 15¡ sÎD. DEV, È 151 COEP. OP Sf,Et -
lorts:
1. 1¡I PLOOD PETTS P¡¡O¡ TC 1965 ¡ERE DBRIY'D P¡OII OLD
II?EÊ-LE'EL IECORDS. |IO ¡ÍICI I COITRI?ED R¡TI¡G
COT'B CTS ¡PPLIED.
2. T¡t 19t5 rfD 1951 ?r,ooD pE¡is ¡B8E ît[Et tS lnr LlrcEsr
ItD SBCO|D Lt86ES1, RESPBCTTyEL!. It îfl8
1902-76.
pERTOD
s¡tt 69621
ROCtrf COLLT P ¡1 ¡OCiBU¡r
ttlgllu!î t¡El, s0 ¡r . 22.0 i¡p REprBrrce slrc:367601
lolDll O! ¡ttolL PEIIS - r¡ pE¡IoD oF ¡Ec. = 1966-76
Itr¡ PEtr rBtS PEli tu ta PEIÍ tEtS PEtf
19ó6 to.z 1967 tr.l 1968 19.3 t9?O j.2
lltl 7.3 1972 51.6 1973 3.9 r9?q 9.¡
1 975 7,8 1976 9.6
llll | 12.7 STD. Dll. . ltr.q COE!. Ot S¡EC - 2,63¡0
lotls:
1. 1!! 1972 plooD pPttr sts 6.0 ftrEs Tf,r t¿Dltt rttorl,
?LOOD PITT I¡D ¡IS îEB¡ETO¡E
ptollttlM
O;IITED FROi
pLot
l8g
ttDsB noLE ro.2. f,o¡ztER, rT
II3 ITCLIIDED ¡I î!E DENTVIIIOi O' TIE
oltt¡lllstD cÛErE POR 1ñg lREr.
2. to tfltttl pElr gf,s ¡vÀILIBLE ron 1969.
7. SOUTH CANTERBURY DATA
ïï______u:9:
cttclttlr l¡lt, so i; =
tolltt ot Ittrrll 9E¡rs =
l8t¡ Ptl¡ rE¡B
t96¡ tl. 52 1965
r968 32t.53 t969
19?2 296.83 1973
1976 5r.56
PETI
t2 1. 14
63.98
98.16
llll . tl2.?0 sTD. DE . .
srlE 69506 onÀRr n 11 srLvEltot
crlcÍiErT t8Et, SQ fi . 520 lltP REPEnETCE
TO'IE8 O? IIIOIL 591:730081
PE¡ÍS E 15 PtRIoD o? RBc. = 1960-tt sltt 7rrt6
tEli PDil( tÊtn PPri rE^t
1960 r70
PEttr fElr P!¡f,
196 I 4SC 1962 I
1961
lC
l¡0
1963 ¡t95
f965 1tt7 1966
1968
63
2t9
1967
cltcRtrfl t¡!1, s0 rl .
29a
t96ç 5: 197C
1972 ¡t5
317 197i lolllR or tttûll PE¡Ís
98
=
1973 125 '1974 263
tll¡ PEtÍ Ittn
iEl¡ . 26" sTD. DEY, 196¡t tB¡
" 197 COEF. OP SrEt É l..tO?2
1965
t968 1¡5 1969
to?Es:
1972 t86 197 3
l. tfit to¡5 ?Læn ntti op lo0o.cfrtEcs gts llfpf, ts ?nE
L¡¡GEST III THE PERIOD 1871-1976.
llrl = 227 StD. DEl. .
PEIf
234
380
228
899
13
557
12
IllllIlïl-:-11-l:I:l:
iÀP ¡ElEnBict - Sltß:125t12
PB¡IoD ot [Ec. = 196¡t-t6
f 8IR PE¡T P'II
1966 41.21 'Ef,R 1967 65,77
1970 65.20 t971 q8. r0
t97¡¡ r10.0¡ 1975 lOr.06
93.13 COZ'. O? sÍ!¡ . 1.7422
lto¡r¡I R tÎ sottîf lrItDEi
llP IEPEFE|CP = Sl0ß:¡50406
PE¡IOD Ot ¡BC. = 196¡t-?5
fE¡A
1 966
1 970
t97ll
PEIß TEIF PETÍ
259 t967 39¡
262 t971 t05
13? r9?5 208
90 COPI. OP s(Et = 0.8171
sIrE 596 t¡
crTcf,is¡r t¡rt, sQ ft =
lofBEP O? tftutl PElf,s:
rlr¡ PEtf tEtR
¡56
oc
oPoÍt F lDotE stlDlot
lltP RE¡ERn¡C! = s10t:54t902
PEnIOD 9P n!c, r 1917-76
I¡IR PRTß IETR PElT
1939 s0 194C !23
19f¡3 1a2 19¡rt 218
1947 q0 19¡8 216
1951 666 1952 5ó5
1955 111 t956
1959 50
230 1960 124
1963 542 1964 t3
1967 293 1968 It9
1971 175 1912 306
t9?5 30? 1916 147
PEII(
r9l7 25 1938 19ll
l9¡l 36â t9¡2 46(
t9¡5 e¡t t9¡6 91
t9¡9 r90 t960 5q:
r95t ¡00 t95¡ t52
1957 , 666 1958 2(,¡t
196t 36t 1962 69
1965 520 t966 7t
1969 127 197C 321
lgtt ¡5 19t¡ 1¡'
l¡¡f = 270 ST'!. ¡Et, = 2C2 COp.p. Op SiE¡ - t.Ol57
TOT'S:
1. T[9 lqIfs PRIOF T: T965 IERE DERTVEÞ FROIi OT.D
fllEF-LEttL 'LOOD RECORfTS, TO rFrCfl t collRrvEn Rlrrtl6
crttv? fls tPPLIS¡.
2. .ilr l1¡5, t,rst rxD 195t FLOOD pEtKs fpnF lrf,pI ts !8t
7T:?ST, S'COllD tttÞ 1fiIÂfi L¡Rersl pEtf,s. REspEcTIvELt,
Ix .rfF PSR:OD 17C2-16.
71128
IRISIIIX CREEI IT 3ITDT RIDGP
CtlclillT ll¿t, sQ ti = 1tt2 lllP REPERBICB = St00ro92880
tûlllR ol tflûtl PEttS E 9 PEBIOD oF RDC. = 1963-71
tll¡ Pttf rE¡t PEIÍ
1963
IETR P¡ITT
31. t '196¡
PE¡T
18.4
1967
1965 20. 5
79.3
'ETR 1966 11. r
1968 31,2 1969 c6.5
r97t 197C 73.0
t3.3
¡Btl ¡ 36. I srD. DEr. - 25.2 COEP. OF SXE¡ = 0.95rc
srrr 71129
FORßs P I? BILttORTt.
c¡lcnlllT lllt¿ sQ f! = tr0 itP ¡DIERricE = sR9:035017
lÚltll o? ttttttl PP¡rs s tt PESIOD Ol R!c. ' 1965-75
lll¡ Ptrf, tttn P!ÀK .'EIR PEÀÍ
't965 16.7
tslR PEtr
t966 25.q 1961 50. I
1969
t968 19.1
12.6 1970 3¡.0 1971 12.6 1972 22.3
t9t3 20.6 t97¡ 12.0 19?5 r8.5
lE¡l . 2¡.0 STD. Dtt, - lt.z COEP. Ot SrE¡ =
104
Water & soil technical publication no. 20 (1982)
.i.

71t35
JOLLTE R lT 11, coox slllfo¡ SIIE 7850't
clIcElBrT [R?1, SO tr¡ = 139 lllP REIEnFICE = s89:8tl1164 ctICHiEllT tBEr, sQ xí 160
tOiDlR OP ltt0ll PEIÍS E t0 PERIoD oF REc' = 1966-75 t{0llBEF OF tlllûtl PETKS = I
trlE Ptl( fEl¡ PElf tETR PET( YETR PETI( IETR PPIK IEIN PETI
1966 97 1967 106 1968 49 196q g0 1958 r¡l.C 1969 26,6
t9?o 72 1971 31 1972 ¡9 1973 62 1912 55.7 1973 19.8
r9t¡ 30 1915 60
liPttl = 10.0 S1D. DEY. =
rBll = 6¡ SrD. DEf' = 25 COE?. OP SrE¡ s 0.t¡152
8. OTAGO.SOUTHIAND DATA
sltr ?¡337 trlEB0Rll À l1 ll.E'B.
cltcttrrrl llEr, sQ fl =
IÛIEEB Ol t¡ittll, PB¡ÍS =
376
I
ËrP REPERUfcE = sll5:935593
pEBIOD Op EEc. = 1969-?6
rll¡ Pt¡i rElR PEIÍ
t969 13.2 1970 22.6
19t3 23,6 197¡ ll3. ¡
ll¡f . 4t.5 STD. DEv. =
tEÀB PEIK IEIR PETT
1971 79.5 1912 ó4.4
t975 t10.5 1976 62.1
23,2 coE?. or sf,E¡ = 0.1372
srrE 14625
ctTc¡tiEltl ¡nBr, sQ Íl =
I0IBEB OF txiûl¡, PEÀÍS =
rrta PEtf lEtl
1964 21,3 1965
1958 84.5 1 969
1972 65.5 1973
1976 ¡r3.1
lEt¡ = 45.9 sTD.
srlE 78633
PETf
30. I
59. l
25, e
1C9
t3
ctT¡roPtr I tr fPftrfcfot
IIP nEttREllC? = Sl77:4310r¡5
PElIott ol nEc. = 1968-75
IEIS PEIf, I'TB PEIÍ
1970 25,0 r97l 17.1
197r¡ 31.9 1975 22.O
12.8 cogî. oF sit¡ = r.3586
:11::11_l_ll-:"'ll3ll l!:
lÀP BllERPrcE s169:122516
PEnroD 0r ABc, = t96¡-?6
rE¡n P¿lÍ rt¡R Ptlf
1966 30,2 1967 32.O
1970 67.8 t971 t2.ø
1974 34.5 1 975 33.2
18,5 coPP. oP SÍEI = 0.8196
ilÍ¡BBcr B tr l¡EEurl6 lÍs.8.
slll 7t3 r6
I.OGTIBI'8¡ I ¡T PÀERIO cttcfltrfl rBrt' sQ ri 13q0
loiBER ot lfl0l¡. PEIRS = 9
iBlt = 359 sTD. DEY. = 2tl9 coBP. oF sfBt = 2.3010
Cr!CI!E¡T l¡rl, s0 trã r5O rtP AEFSRE¡CE Slq4:624217 IETB PEàf IETS PEIi
rutB!! oF r¡¡sít isrrs = 10 PErroD cP nEc. = 1967-76 1968 ¡t1.0 1969 t7q.7
1972 269.2 1973 tlr6. I
r!18 Pltf rEta PEIÍ rEtR PEIX fE!! PElr
i,at s.r t96s 20.6 le6e 12.2 le?o
1976 248.0
22.e
t9t1 35.5 1912 50.1 1973 21.8 197q 15' 6 rEtI = 216.5 sTD. DEv, =
1975 26.5 1976 15.8
rrll = 22.6 sID. DtY. = 12.7 cog?' oF SiEl = r'0925
srll 75212
POIITHIXT R ÀT BÛNÍES PORTI
CllcÍrErT lRElr SQ Kl 1332
tûrErB oP rlroll PE¡rs = 13
Ílp gEpERt¡cE s,11.1.22t¿r12
PBRIOD o! FEc. = t963-75
tlIT PEII
PEÀÍ f8ÀR PttÍ tLlR Pllß
1963 337 'gIR 1964 8¡ 1965 310 1966 276
1967 ¡66 1968 536 1969 2t9 l97C 255
1971 370 19a2 1068 1973 170 1974 201
't975 318
tolBs:
I. TIB 1972 FLOOD PEÀI( ¡TS ?88 LTREBST IÍ TgE PEEIOÍ)
1958-?5. fT CÀS OirrTED FROü TEB lItLrSfs ttllDlR
BÚLB TO.!, BOT ÍIS IIICLI¡DED 1I¡ lEE OERTYTÎIOX OF
lEE GEXBATLTSED CURVE FO8 lBE IRET.
itP REtEREXct S177:331139
PDSloD o? RUc. = 196C-76
tEÀA PETK IBIE PIIß
1970 168,4 1971 201.2
1974 1:t5, ¡¡ t975 t9¡1. 1
05.1 coEP. o? slBt. 1.605¡
Water & soil technical publication no. 20 (1982)
105

APPENDIX C
Summary of tho data for the
Nelson area
NETSON DATA
srlt 57002
tloÎUErt n l1 8¡10t BIIDOT
c¡IaEllE¡r ¡8Et, sq [ü 164"
¡úiBEA OP trtotL pEtis = iB
ll!! PEIK rErR PErf
!!93 7s7 reso s83
!?18 s83 tese 75c
1963 561 1966 325
!?!? s6r
1973
rsze izt
r 159 197¡1 2622
ItElll = 1078 stD. DFv. = '
lloTES:
lllP SEP9REÍCz . St9:2O33OO
PEAIOD OP REC. r lg5¡-l¡
ïiìt i3|T üi; !¡äT
i¡ï ,¡33 t3:3 iil;
t9?t
t. ¡o-rtrltolL pEtßs ¡aERp tvìrLtBrE poR r956,1960,
1964 tID 1965.
2. olrlt of,E ?¡r¡îÀîM R¡ÎIÙc c089E I5 tvtrf,lB¡,E,
s16 1972 rjes
70t¡ COEP. OF SÍEt = -t.6331
IÀIGTPEÍ¡ N IT SIIIG ERIDGD
c¡1c8llE¡1 rREt, SO Ftt - 373
IU||EPB OP ÂXllftÀL PEIÍS ¿ o
!9!R P¡At( rErR PErf
!9qt 467 1e62 467
1966 q7 196? 3¡0
1970 2â9
lllP REFEREnCE = Slo:072t¡l
PERIOD 3P REC. - 1961-?0
iiåi 'ååi i3åt "åi5
1960 607 re6e iì ¡
ËÈtl¡ = 39¡ STD. DEv. =
l¡oTES:
174 coEP. o? sßFt = -0.24?5
l. io--Àrilut¿ pE¡t( 9ÀS ÀVtILtBL? ro8 1965.
-'. ôtrLr o[E TFrrtrrvE FÀTfrc coav¡: ¡i-ii¡rrrg¡,g,
srtt 57106
slrrLtfBROOR I tî BtErr¡s
cllcãttEÙT ¡RBÀ, SO K[ = 81
¡ollBDR oP Àùt{rrtL PE¡KS = 7
M!
P ¡ÀK rR¡ F FnrÍ
!?10 48,r¡ tq?l c8.s
197tt 96.8 t97q 3n, c
iEt[ = 60,6 sTD. DEV, -
IAP REfpRt:t{cE = St9:2Og2tF
PERIOD 0p FEC, = t97O-76
ïll! PPrr rE¡R PErrl
l?1? 103,6 te73 it. t
ta76 50.0
27.9 COEF. ot sÍEt = 0.9692
106 Water & soil technical publication no. 20 (1982)

24 HOUR Í(AINFALL P OF RETI.R,N PERIOD 2 YEARS AND ITS STANOARD ERROR' E (III4I
NUMB ER
Nur'IBER
-o
ãt
f.
Ø
CL
ñ NÞ
Þ !!m
z I-
x I
É? r-r' a, Âa 8e 12 t2 f{ÄñGnNUl I{ANGOf\¡UI
43950L 34 59 173 t2 r01 1?
HAIHARARA
439201 34 51 l7J 12
87 e r{AiAmi- BnY- 35 2 t-t3 53 999
856 RANGIT IHI 531301 35 6 L7? 2A 9t 1l
KAITAIA AERODRDTTE 530201 35- 4---113 17
triËîmilunr- -- ---si67az-tt
z--îrtr
ìîiiåìä--u u rv'r'-- -nl-zît- :z {'i- -irã-fz-- eo--i 2
ruaffi o r 35 I 173 30
--91-TT
AI{I PARA --sallt¡f -- t5-Tõ-T¡t
5a28ll 35 13 L73 52 L5¿ 15 KÉRI KER.I 532SOt. 3' L4 173 5?
el I
g¡¡g¡1P0LL5328L13513L73?_1--L5¿15KtsKIl\trKL)2L7wLJ¿!-LlJ'l
-¡to
TÃ-rrAN-Gl rdRE-si- - - -542õor ãá-i'ç -i1e 137 t3
--llggl- i: l: ìl: i: ee L5
RUSSELL 542LO1 35 1ó L-t4 q -
108 1 HERÊKINÛ
532202 35 1ó L73 13
EEOIõÍõOD-- ltzzli ;,; i¿ ltz-2T---ca 1ó
- 523502 35 l8 113 33 89 13
-uHnwenr-¡¡o.z
OKAIHAU 53319t --il zl-
TaI- -1-i OPONONI
534402 35 29 173 ?6
KAIKOHE AERODROMI ME
----8151ùI--a-;
5348ii1 35 27 L73 t3 49 l?? 13
ti- Ir14 t6 r35 6
PUH I PUH I
a462A2 35 36 174 150 Zl sANDsTWHANGAREI AREÂ 546411 15 36 l7+ 26 1?0 30
HIKUR ANG I
RUDER9{ OVRE --5767I t-- -$ -17--1ar4l- -- --12õ-"0- -TÍ-EFñCF;¡FANGARÊr. 53óó11 35 38 173 te t2r 13
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36 45 L74 43 100 12
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TffiEFõ.- -- --152-oo-t-- 74zsa3 3? t3 LT4 i4 69 6
3TT5_-TIE--r- ----ÐÃfù --------
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7-4¿6ùI--7Tre
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'Frir{fTsr-riFu rfi sT{isT
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Ti{ANGAPOUA FOREST
ROCKV BAYTI{AIKEKE
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TAIRUA ronesTl,lARA¡TARUA__EQR
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TE KAUI{HATA
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750802
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36 46 L75 36
36 175 4
37 'O 0 L75 5r
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75tBO2 37 t0 175 51
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75t60L a7
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18
ITHAREKAI{^ 751801 t7 9 L75 51 153 20
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-t525tt 37 t4 L75 34 115 24
trEBE?-F,I1I
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74394? 37 ?L t74 54 88 L2
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te rnoxÀ ----------- 755?ol--n z{ 175 43 ñ7-z---äî-rür¡ =ffiftn-ffi
HAITQA _ 756602 ?l 36 L?5 t6 -r_o_ó__ 88 15
ffi-?5ó
ffi
Water & soil technical publication no. 20 (1982)

TE PI'NA 766002 37 40 176 4 123 l8 TAURANGA AERODROI{E 16620I I7 4A 1?6 L2 TOO 6
RIVER R0AD _llé!_qz 37 4r t75 LL ----
8e-13-- NGAß-uA--- 7s670l 3-7-ri-r- 175 42 87 )6
KIITITAHI 1575Ot 37 44 L75 ?4 97 l7 I{HAKAHARAT¡IA ?ó7OOl 37 44 17ó 0 L66 27
TAU¡fHARE 757401 3? 45 t75 2? 94 15 DUNROBIN,OKAUTA 757801 37 46 175 51 115 l?
È{AKETU T674OL '7
46 L76 27 I18 21 RUAKURATHAMILTON 7s'ttfJl 37 47 175 le 69 5
RAGLAN 748801 37 48 174 53 e2 l? HORRINSVILLE DAH 758503 11 48 L15 15 96 L7
758ó01 37 48 t't' 4A_____!49 18 -- TE PUKE 7ó8302 37 48 l7ó 19 ll5 L2
758001 31 49 175 5 83
? itaTÂHÀ1Â f,tATAr,tATA 758703 A1 11 49 t't5 L75 46 107 1ó ló
PoNGAKATaA 76840L ?1 19 176 29 L25- 20 RUKUHTA 758301 37 50 I75 l8 69 4
TE PUKE NO.z 7ó8303 37 50 L76 29 135 L2 I¡IANI ÂTUTU 768402 A7 5L t76 2'l r3l 2l
HAIIILTON AÊRODRCIHE 758302 5? T75 20
716203 3? '1 57 t75 L4
85 15
81 13
t{HITEHALL'CAf{ERIDGE 758501 t7 52 115 3+ 93 15
CAHBRIDGË- 75940,4 37 s4 176 29 89 l?
76920t t7 54 17ó tô L53 L2 ROTOEHU FOREST 76e50L 7? 54 t76 ?1 130 9
THORNTON 769601 31 '6
176 52 9' I
74 52 ?5 lt KUIIANUI 76eSO2 t7 5T 176 51 108 l4
EDGECUI,IBE 7tsso3
-¡t =8 -TÈ 48 9E ll I{HAKATANE 166
ROTO-O RANGI
Tiño-EiTF
75e401 37 5e
iÈ ieio HunsEni eoo_gq ?? 4 lI9 1? l3-9 ?l HAIN9I'I{HAKATANE 9?9901 1l =2 IJI =1 llt }g
TAUi{ANA @ 3s T lre ¡o loo 11
KAI'HIA 840801 38 4 L14 49 78 t? NGUTUNUT 850003 38 4 1?5 5 Lze L29 2L 2l
ffi--8-66oéi-'aã-=5- -rTr-2T------RAnEmu --
ffi---Ér4õr-18-1- -ii
ARApUNI pohÉR sTN. 85có01 3g 4 ?8 5 NootrGltnxA 8ó0101 38 4 17ó. 10 132 lô
OpOURIAo s?oocz 3s 5 LT7 o 1?ó 4u LA{E aKATAlx¡- 8ó1401 38 6 1?6 26 l2l l2
ROTORUA AERODROHE 8ó130t 78 , 7 175 le 114 16 LllHFIElQdglfepRU 8518Û1 38 I 175 50 e9 17
8?1003 38 e L77 5 110 e
ÎARAIIERA FOREST 8ó1óOI 38 8 176 39 L49 1ó }IA IHANA
-G[EñERõõR- -Bl7zfi+ 18 f0 175 t2 - ---?5 -t-t---
I,IAIAHINA 8ól7cl 38 l0 -T-zr-- 1l-t6 +7
-wnã(ÃEEx¡ RE¡¡A -_------ 86 12õã- 38 To Tt-r 6- lr0 9
r50 zo HATAHT 8?2102 38 ró rJ? .
re
? rÍ1
r)0
?=r
|TATPAPA PoþrER ffi fB 1?5 41 90 13
s6?4a2 38 18 176 24 lIe 24 0PoKoTUTAR.IRUA 8ó3803 38 18 l?ó 50 L24 23
ROTOIIAHANA
-mmTTOlo --8t3ãõT- as 2o
GRANT RttTKOPURTKI 863!02 38 2L
ã ffi---E4tð01---38 2-
TAIOÎAPU FOREST 8ó3401 38 19 176 25 8l 7 TË KUITI 853104 3g 20 175 s 66 5
176 48 LZ3 24 NGAKURU
só3I02 j8 22 t7ó 10 eo t3
KAINGAR0A_ F_orq9_r 9q1æl 29 2-l 17c 5Z- - -tl -
Water & soil technical e- AT TAI{UR I POWER sTN. 864003 38 24 17ó 1 IO8 I5
r_7_6_ 3_! j publication no. 20 (1982)
\). ?!_ - ___quMEl4!_rProPIo ,=_ 844801 1s-4¡ L-t4 5t tol e

o
NUI,IBER
HHAKAIIARU 854801 38 L7'
EIIITEI-
--T-646s1 '36-25'
48 93 13 OHAKURI POI{ER STN. 8ó4002 38 25 176 5 97 I-E
tT
4t-----r,T8 21- -.- --ùun-uprnÃ
8ó470t ,8 21 l7ó 42 t4l 30
GALATEATNO.2 8ó+704 38 28 t?ó +6 9ó 1ó PUREI]R,A FOR,Ë ST 855501 38 31 1?5 33 195
L-t4 52 91 I llA I RERÉ 855002 t8 ,2
rA¡RAPUKAO FOREST
LT'
8ó5501 38 32 l?ó 34 91 6 TAHORAKUR I
865202 38 14 1?6 L4 e9 ló
PT.INI¡IA¡ ARIA
85500 I ?8 35
-TfmFEI¡F¡nU
t75 0 78 e HAIRAKFIT SOIL.CON.RFSgóó102
-ao6-e-01, tB- 37 Í71-5T - -ttä2_t- --- -nu-aT-- 38 31 17ó 7 97 l4
A
sóóeoz 3¿ 37 17ó 58 -64-6_ 8l
¡IA¡RAKEI POIIER STI-I. 8óó1OI 3838
l4
l?6 ó 8t 1 TAÜHARA FÛREST 8662A1 38 38 176 t3 96 L4
ffi-85E9õT
'
z6- r-irt-ET- -- -E.4 f 5- ---- -- riI-ñõrNuT-FÐ'{ESr 8óó701 38 39 L76 44 887
lAUPO 86ó002 38 4l t76 4 75 ó TAUPO
8ó6001 38 4t 176 5 óó4
IIO{AKAT INO STN,I.IOKAU
ffi__-
847601
86 8001
38
38
43
57
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t76 5 t21
14
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I{AIMIHIA FÛREST 8ó8201 38 50 17ó 1ó 81
ilAPTER ilITD DISTRICÍ
LOTll{ POINT
-IIÃT-ARTU--
IIAUlOTARA
GATE ST ATION
RUTÎORIA
HHAKATANE
-rmmR-EIlü-sTÃT1-oNiloTU'
IAIFASA
-7¡r-ó-0öf
785101 ?1 33 t78 10 tló 15
-3-t-4: -1-?€---E - -T3r -6---
7812A2 37 43 178 14 180 16
-7EE-00r 37-5T--178-5- - -T4r-T0-
78e301 31 54 178 19
tO8 lt
TË ARAROA 78ó301 37 38 178 20 ttz 9
- E-Ã S f-e ÃÞ E- [T-GFTt.|o u_s tr_ 7-s750T--îT- 42 - -TT8-5T -----TT5-T
KATOA,hHAKAANGIANGI 787303 37 43 178 18 150 9
--TíÃRÃEMII-S.CEOEI- T- st ,¿ Lrt 5> llr z,
?8e201 t7 57 178 L2 112 15
TAOROÀ STATION
769eO3 J1 58 L76 57 100 I OPOT
-88trI-0-1-
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IIANGAfUNA I TOLAGA 8AY 88320t 38 te 178 16 1û2 L2 t.IATAT{A I
873501 18 2t t77 32 t03 I
KORANGA STAT¡ON
--RTFõT;ÎE[ãGÃ_B-AY-
PT.tHA
' ñõR-^-IRAU r Þ¡rÄqÂs
IIA IHIRERE, BEC KINGTON
HAERÉNGA O KURI
GISBORNE HARBOUR,
874301 38 25
B$4ãUI- 36 25
874841 38 28
884201 3e 28
815903 38 35.
t77 20
-f7gre--
L11 50
'
l?8- 15
L17 56
87ó801 38 41 l-?7 48
88ó001 38 41 t?8 I
PARIKANAPA 811701 __ 38 _4å_J77__!?_ _-_ .
oNEPOT0TItAIKARET,TOANA 878lOt 38 48 L11 1
PIHANGA 878401 38 48 L77 26
--89---E---
131 2t
586
846
?89
102 7
824
11ó l5
lL4 I
108 l5
I,IOANUI STATION
ðT-ol(E-- -
TË KARAKA
EãsTI{ooD HILL
GI SBORNE AÊRODROI¡IE
IlANUTUKÊ T GI SBORNE
EREPET I
874342 38 25 L77
814-d0Z- 1E-2-7 ---TT?
e74805 3A Z8 L77
8?t701- -38 34 - 171
s76902 38 40 L77
876803 38 4t
9?7301 38 44
TUAI 878102 38 48
Í,IARUMARU 8?95û2 ag 54
36
52
43
59
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L44 2l
90 tl
83 12
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775
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177 48 L3t 25
t77 9 109 14
L77 ?2 L46 23
Water & soil technical publication no. 20 (1982)

8??20! ,3-q-
--E[-LLçB.E-SI-ÂBD-K-EE,|,I- -5Þ !17 r-! I09 1-3 _TARE_!,,A_-
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- 8-?-e-q9? ---33--19- W -+9--.-r-8-6-28
144 ZL rcÀNeAfo¡o siñrtronrnç sleltz 38 57 L77 47 L68 2e
HAUI{GAlAN I}IHA _8þ9-9_L?_ V8 59 L76 es-I2---- FRASERTOHN'IIAIROA 91O4O2 39 O _ L71 24 LL' L5
'4 126 1 HAIHUA VALLEY e7}20t a9 3 L77 14 11ó 15
HAIROAT HA IPUTAPIJTA 9?0301 39 1 1?7 19
HAIRoA __- e70403
-L3-]- -!fl-ZE ---
-93 þ _8AUzuNGÀ --9-?q!q1- !?--.1_'-L-71--8 123 18
ll-2- l?_---=-SLENEAÊE-d!olEt'lÀqBt-lfqg93--- 3e---2 r71 2 L4? lr,.
t16 29 Ll7 24
116 42 ll8 9
L76 ?3 L47 22
!7_6L2_ L38 L3
rE RANGr_[AUxqAHA3VßU9-éoqqL-:-9 BEA6H l-VLz?--_
e?osol 19 5-171 s¿--- is tz BLAcK sTur.tp srATroN eó1401 3e 1Û
'AH'A BAIRNSDALE eó2502 3e t? 1J9 19 --
eó 16
---
ESK FOREST eó27o2 3e 15
TAREHA e(,zsoz ?9-16 L76 i{-- tot zz fË I{ATRERE e62501 39 17
TRELII!X_0_E__- - ?6-?1OL 19-t7 -t-t-e +5 - lr-s -1â -t¡l!golq---- ?óæ-Q-2---39--l-s
çL$'¡qÂBB-Y-SIAf'-I-0-IL
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-]11 2+
82 I4
?l
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¡TA IHITI
9ó4?10 39 22 1-T6 4' t39 24
4301 t9
IÉ HAU
9ó4501 3e t76 34 IOL \?
ESKDALE
9ó4803 ?9 24 L76 t13
RrssIxg-IoN -- -lé4191_--.7-e--21,,11þ -!3-'--115 l7 16
- _-N4P¡E8lE-8qp8eË-E--- I{A IHHARE
e644tl 27 "4 1?ó 29 114 l8
5A
eó4801 '9 3?,-2Q- t?6 52 8L 6
SHERETþEN ____2-þ5Lo-L 3e 39 -Lf-g:9----l-u--1-q ---NA_?I.E&
--9q??91--?e-99- r?ó 55 81 5
*HANAI.HANA e654ot t9 3t-:,:.(, z6--__-104-tã cor-onsri Þooío 39 35 176 30 e0 1ó
x¡ururu qoszgl 3g ¡¡ llg !9 lo3 20 TE KATAÎA eóó3ol 3e 37 L76 23 82 LO
RosE H¡LL s665o? ffi s4 Lt xlsr¡nc,s -
9óó8oL 3q 39 1?ó 5l ó8 o
HAvEL_ocK N_o¡¡Tll_-- -e66soe
3e 40 L16 it 82 I
---- eó6901--3-e-41- l7ó 55 - ?3 5
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r{HA_r(A.!uô_ _ e6!29t ?2 !? }I9 ?-5 eo 11 7e 44 t76 27 83 5
TIHAKARA
Illâl\^ñA tvtLvL ¿' -'
----EI-A!¡-s--Eg-tsËlT-
-?6!!9t
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GHAvAs þlAvå)
cl'tlõt ;
--
::::ll * i3 ,aA Eo o? A
j-rqrq¡N-D- --
jt-r9- ãi s---
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TLL 9ó8410 39 5l L16 22 90 ló S ILL
9ó8802 39 l7ó
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232
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liiirjårñU__' _ ____qqlgf-jg a \16 32--þt--!-
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HOUNT VERNON
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968303 39 5l L76 23 89 l5
s3
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9
969
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rA¡?UKURAU6A5g340c1?633--TIgROTOI|AIóo?o24o0t?ó43e',15
FOROALE
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Pt KERANGT _-_ TTZ-TiffiTATION ó0602 q
KopuA q 11_ __i__z_ _ _TËHpLEts ILAT_- __- _ 60?ró _ aa---5 ---!1Q-iL
t32 le
Water & soil technical publication no. 20 (1982)
-
-

l9
AT
NU¡IB ËR
AR',tËtlANA ÂRAIIOANA
ó1801 40 9 176 50 90 t3 RED OAKSTFLËMTNGTE¡I
1õ
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10 1?ó
l+6 TË rF RE|IUNGA RFí{uNc z 7 69 l0
-arooi 626a2 40 -----

955902 39 32 I75 5T 54 7 MAUNGANUI IVIOAþIHANGO
-TIf_fa'_=9-ã' -T14-1I------¿I-1--6 -- _-- o-FÃFtr----- - e55801 !9 t4 175 5l 578
s+szo-r tT 7'---T74-TZ 64t
955?01 i9 t5 l'75 47 ó0 9 KOHHAI HLSIPUKÉOKAHU
95ó701 3e 40 LT:2 +2
- -5e
eóóoûL 1? -3-7^JLó_=¡.^-- 70 J9,
I HITFI'TAIHAÞE. Þ1636i- '17 -lí---1,75-ÈÕ: - 54 3
HÊSSElTrlAûR0A e5?eot ae 42 L75 55 64 LO
95640L 79 4l L75 25 ó4 10
UTIKU SLIP
e57S10 19 44 1?5 50 óo 6
PAßI},IAÜHAU
957ZOl 39 43 115 14 78 13
Ërltr
947402 39 +5 r74 28 90 L4 UPOKOPOITO s57to2 39 45 1?5 9 78 tl
F.^VZÁ
foqtç EsrArEs
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TAf,UA
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--
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TLoeKHotrsE,BtJLLs-
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6?.¿r'rr LO ?õ 175 24 6
53ó05 40 23 L75 77
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54442 40 26 ]31_ 28 51 TIRITEA NO.2 54604 40 26-_ I75 40 92 L?
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HILL r L If'rTON 54502 4 o
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4 HAITARERE FOREST 55201 40 33 I75 12 ó6 8
775 I.IANGAT{AIRE
t{ANG^t{uTurPAHIATUa-54801 +o zl tts r'c 55?01 +0 3l L75 45 96 1ó
FltlNl'lmulvtr,{n¿¡
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IIANGAHAO UPPËR Sç+O¿-?O 38 -ttS Zg Lz6 tó LEVIN 5ó?02 40 3e 175 tó ó0 ó
Water & soil technical publication no. 20 (1982)
l1
L?

A ON LAT. STATION NA
NUMBER
AHUNA
5ó701 40 19 t75 +
MOUNT BRUCE
7t 01 1õ 46 175 9 532
I{A TRER HURAUA
I(tPÎHANA STN. IIATATKO 612ÚL 40 47 KOPU
ROSEBANK'BIDEFORD 58891 æ 5l 175 51 69 9 AGSHOT STA
PARAPARAUÍTIU AIRPORT 4990I 40 54 174 5e_ 6ó _5 __ HARANGAI STAÍIÛN
TINUI DOI{NS STATIoN 69AC2 40 5+ 17ó 4 102 1
llAIltcAHA'HAS-IFRT0i\|-- 5q6-04--¿¡--5e - r7'-57----6t 5 --
GLADSTONE,TE KOPI I5O?01 41 L L75 42 69 L2
PAEKAKARTKT Hr LL T4o-06T--4L---T-'r71-'6--só t2
IIOODSIDE
L503A2 4t 5 t15 23 --
TITAHI BAY
ffiunñrFloõf
GLADSTONE IARAHURA
KAPTTI ISLAND
LIlIOEN
AYAI¡0Nr LOI{ER HUTT
IIARTINBOROUGH
IfADD¡NGTON
L4L8A2
I 5tó03
LOI'ER HUTTTTAIIIA ST L4?9TZ 41 13 L74
c - +î-r+ -L-74-
PURUITINcA.t'tARTIN30R. L52501 4I 14 1?5
ffi---I4TeTÇ--fi-Io-I?ã
HIKAUERA t526t? 41 16 t75
KARORI RESERVOI fì
-Offi¡ñõÃ-rA-YcLENBUR,NI
TE I{HARAU
IETCON HILL
BAR¡NG HEAD LIGHl.
STATION
NUT'IBER
57501 40 45 175
5780t 40 TÃ
5 8óOt 40 48
587A2 æ ñ
69001 40 54
t75 7'
I
176
35
FI
40
æ
o
t09 t3
8
a2
CASTLEPOINT LIGHT. ó9201 +A 54 17ó 13 69 t0
¡{A TRARAPA CADEI FARI{ t5Gó01 4t o l7s -€--T-I-T'
r5080t 4L 2 tT5 53 959
1502orc
r15
82 t2 GR€YTOhN
150401 . 41 5 t75 2S 61 10 5
41 6 174 51 _q e q!{L_LÅGFTP0NATAHI 151501 4L 6 t75 33 72 t2
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4l r I75 66 I
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t5too4 4t t?5 3 72 e
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43e01 40 51 t74 s6 7t 6 TRENTHAM 15tOO3 4l e tT' 2 - 8? v¿ 15 a¿
f+TEõI---+T-fil--I74 - 76 e ---Iõr'¡oeu-SH ERrñef-Sri,¡. -ffi
r+r"/u) 141905 4L +I II ll rt4 174 56 1þ- 16 5 TAITATLOWER TAITÀ.LOWER HUTT HIJTI 14l9OZ t¿)tqo2 4t tt lL tt I74 Tz¿ 58 qq 93 o", lO rn
- L5t4oz 41 11--T75-e-- aa àr clirvsto¡ L4zsol 4L Lz L74 4e eo t5
-- -!l??07 !!- \2 L't4 51 7_l É I{ATKQUK0U,LONGEUSi{ 1526ü3 4L L2 L15 36 58 s
5+ 18 e hrA¡NuroRU vLY.rNAGATAl526ol +l 13 t7i 4t ?z
--_......:---_
13
,> a+ 9 ËAHAKI t524A4 4l t4 175
306û9
25 57 I
t{AKARA L42143 +L 15 L?4 42 83 9
L4270L 4t 17 174 45
rz3601 4i Ia Í74 tl-
153801 4L le 175 5l
5 s - r 1A-r ¡- -
--fÃTõRmc-õ-,rTT-- r5210r 4r r6 I-75---9
J1 80 14 ¡{AIHOANA TE }II{ARAU L52tO2 4L 1ó t?5 53
9Ce
8C L2
82 13
---TB66T - 4T-26 - T74--5õ ---T a--t-5 -
144891 4t 25 t14 52 78 L7
FAREI'ELL SPIT LIGHT. 35OOI +A 33 N3 L 74 3
-TlITEEnt--- 26401 40 4-I -11-I -z-Ç - 75 -1
tArftA AERODROT4E 28701 40 4q t72 46
lO7 I
ffi - -T2osor-4- T- r - - i-tz-E c- -fr c z s-
llos3 BUSH 120elo 41 3 L72 55 t14 12
Water & soil technical publication no. 20 (1982)
KËLBUTINTWELLINÈTON 142702 4L 17 t?4 46 71 5
noNogr-lr --_ r+aeTe
-a[lg-il{-l! 7l tz
-- ?9 ll
IlÇsEût-H¡ -
__ _ TETLINGTON A¡RPORT 143807 4t 2g L14 +9
8?
EE IZ
ó9ó
CAPE PALLISÉR LIGHT. 156301 41 37 I?5 t8 789
STEPHENS ISLAND LIGHT 4óOOI 40 40
- - aÃlñ¡rIr.r ---r15õt -4O-"6 -
UR,UTHËNUA 29801 40 59
TITIRANGI RAY
RIHAKA VALLÊY
140IOZ +I r 174
L?aeoz 41 3 L72
L74 0 578
t72 3? Leg 25
t72 49 r7l ló
9
55
erTt
133 tó

COBB POTIER STATION
ßIIAKA t IIOTUE KA -- rzl-ttrf
ÎH¡'IROTHERS LIGHT. 1414T1
1 2070t
-6- -LïZ 5F--
_-IûI--t Þ-etKo-KiÑ-l- ---TtI963--41--6--TTT-56-TI-ö-T4-
ffi-T4[OoT-
4I
TESIERN L oTFÅ xqvr Ej' i 1_4 e_q_1
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-4-1-
41
5 t12 44 149 ?4 COBB DAH L2l6A2 41 6 L72 41 118 9
6 174 21 69 13
T---T7T-T-_-LTT_N
7L742
41 1ù 112 58 88 e
T4-17- - -- mlrE_ï rurFR-tr--
84
57
ó3
HDTUEKA 131002 4t 1 L73 I 118 1.8
IZ1eO3 4I e L7? 5e
141002 4l 10 L74 2
}.AITARIA 8AY
ïHAHCA¡|OA 2 1315û4 4L 11 t7? 3t t44 ?5 COLLTNS VALLEY 131503 41 rt r73 14
rjffiRTFo_T-22aõr--¿i-rz--_IT2-5o-__T3T2o----__FtanÃKEK-_-13200_T-lT-I'-1?'-_r
TFFIEEY-- ---rrzrol--4Tar-T1a--é----6r--4----TEt-gctr FRo-õRTrr4-F-.-T!2-62ffi
ffi1¡_qKSI4ZOOr
BËNE AG LE
GLENI{AE
SEAVI trll
LZ3 ¿>
L54 24
l3ó 1.5
nAI.vALLEy L32501 41 t4 t7a 35 t41 14 THORPÊ L22802 4L 17 112 5L
6t-
NELSON t7¿¡.o1 41 L7 .173 18 6e 4 r.lA ITAI VALLÊY L323A2 4L t7 173 21 141 26
HAVELOCK l327OL 4L 11 173 46 146 24 LIÀ¡KWATÊR
r32Súl 4l t7 171 52 155 26
çT-TT--TTÇ-T---T0-g-¡¡ Dltv-E-õ-A-LE
---LT'EOT-4-I T8 L12 55 7' 6
CANYASTOT{N t33ó03 4L l8 113 40 127 ZO BATON
123701 4L 19 172 43 9t I
-HÃgËLOCI( SUBTJRBAN
- 13l7OI
-
4I ?a L17 46 114 15 oCÉAN 8AY
143101- 41 2t taL -'6 109 TT-
KOROHIKO 133eÛ1 41 21 173 58 153 2L HOUTËRE HILLS 13300L 4L 22 I?35787
HOUTECE NO.4 133OrO 41 22 113 96 10 HCUTERE N0.5 l330ll 4L 22 1?3 5 e? 11
lrlot TERÉ No.I2 133014 4L 22 t73 5 9Û 11 i'IOUTERF NÛ.14
noOine nlven r3?:-g!__+]_22---L7-3- !!-- --. e6 -- ó r33t1 2 41221735979
- - - -- BRIGHTT{ATE-1--- .-. 1331 02 4t ?t t7t I 9l l4
-taffirELD NoJ r¡+oo+ 4L 24 173 3 e5 ç HANGÂPËKA
r'roluPtKo -L-?+:99L 1L ?L t246AZ 4l 26 1?2 38 83 7
L72 4e 18 L-2 _!ta I toa__G-o R_GË_ N
q, 3_ _ !34qLó 1LZl L73__5 *__l_04__té_
HARSHLA[q_9__-_ -.- !41-0-ql--!I 2-1 l-21---9 -89
T¡BlANs itÄttgy 135501 41 31 L1? 35 105 1-9 ASnqQ{N siltr!lNAt!Ä!uru!34éQL tt Lq
10
-]:D- 4r 12? L5
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-
_BLEf{HEIr't _.__I-3å_?g¿ - 4L 1r r11 51 5> 3 r2590L 4r ?2 L72 56 108 18
---iiI}lIPANGtl
SEYEilOAKS 135802 +L 72 L73 4e 669 GOLDEN DOIINS FoRÉST 125801 41 33 172 5l 774
FAI Ri{A LL _ 135803 4L-31- ,!73 51 ò5
- - 9
t259or
-lyrrEsFrELD-- - 51,]l- -11_?
!\
13ó701 +r z6 173 45
UGBROOKE r46LA3 4r ?1 r71- -þf
136e40 4L 38 1?3 53
ITAIHOPAI POyIER STN. !1óÞif - 41 4A- -L73-34 -
Lt5 28
554
6_
7
I
79t
93 ll
__L]Þ2Aþ 41 35 -1?3
56 192 19
13ó401 4t 31 177 24 73 e
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BIRCH HILL 13ó201 41 39 I13 11 96 L4
sÉD_qoN 14óOO1- 4! EO- -L74 5.- 7t L6
EAPE,çÂi{e_LËL-L__LIÇl!Ir L-+7 9-t -*-L 1! -L1--+-}1
THE LËATHAM
4L 45 r13 L2 106 t1 rnÊ-H-ll-ooNs 13?9ol 4L 45 173 5e - 84 l8
¡ I lg LÊÃ I I r^r I
rAI rrr \1-!9Q-? 41 45 t74 5 9e \3
AOIEA 137802 4L 47 tlt 4c 77 14 I{URCH I SON 128301 41 48 L12 ?A 653
ÃglE^
- LAKE RoTOITI t2asoz 41 48 L72 5L 1? -J_ - ¿U-UIÅE9!- l387ol +L---]2_ L73 46 85 13
Water & soil technical publication no. 20 (1982)
73 13

â
NUI,IBER
Lü{G.E
ON
NU14EER
I,IURCHIS=ON L¿o,v¿ t283OZ 4L +L 50 )u t tl? t1 ?O 2.9 ó[ ó1 s5 HANGLES VALLEY L284ù2 4L 50 172 24
CHAÍ{CET HARD 14glor 4r ¡o - rz¿ 1r
- -84
ls -- --Srx-rriiE - iããaó+ il-m-iffi;
f.f!99I,.lI4TERE VALLEY 13??91 41 54 L73 34 83 15 r,trpoLE HURST 13e4or 41 5e L73 ?7
xoLEs¡{oRTH
---ZidZdL
CHRISTCHURCH I.iWD DI STRICT
¡IESTPORT AÉRODROI,IE
¡NANGAHU_A _ _ _
II{ANGAHUA LANDIN6
L22lOL
It75A2
I18901
1 1eeo I
4L L5 27
4L 44 fZf aS 784
_41 51 _ l7l 57 s3 ó
4L 55 tzt s¡ ror rr
ERTo}I
I{É STPORT
BERL INS
DUI{FR E ITH
746
776
50?
16802 41 41 l7l 53
117óot 4L 45 171 36 8tå
118001 4l 52 171 50 135 al
22020t 42 4 t72 15 89 ô
REEFION 211801 42 7 l7t 52 78 3 _ REEFTON 211802 42 7 l?t 52 8? 11
LE¡rls PASS 22340L 42 ?3 L72 24 102 e GREyr{ot TH ?L420L 42 27 '1?1 L? 108 t2
OOBSON 21430t 42 27 171 t8 109 1l GREYT.IOUTH 21424? 42 2S t?l L2 100 6
w tt5 tl PAROA 2r5ra2 42 31 171 lO 107 t2
KArrlAÏA 215401 42 32. 171 25 108 9 HAUprRr Z159ol 4? 34 lzt 5ó 99 lO
ffi
HOKITIKA SOUTH 20790t 42 +3 170 57 Lag_ ó _ HOKITTKA AERODROilE 2O7eO! +2 43 t7O 5e LOz ó
LAKE KANIERE 218102 42 48 l7l I 1ó6 2l OTTRA SUB STATION 218501 42 50 l?1 34 183 I
Ko¡aHrrIRANGr No.2 z raoor Tr r:-t7r z t51 21 ROSS 20e801 42 54 170 49 t4? 15
HARI HARI 301502 43 I t?0 33 200 27 HARr HARr 30t503 43 9 t?O 33 L75 25
LO¡|ER llHaTARoA 302301 43 Lz L7o 22 L52 20 wHATARoA 7oz?o3 43 tó L7o zz ztt 2.3
FRANZ JOSEF 303lol +3 23 1?O 11 2"2 19 FOX GLACIER 3O4OO1 4t 28 1?O t 184 23
Fox GLACTER 304002 4? 2S 170 L 215 3? I{AHITAHI 3966c,2 43 38 1ó9 3ó 186 28
3-EmI-
BILLY CAHPTHAASÏ 399301 4? ,6 169 tB ?33 32 MCPERSON CAI'IPrHAAST 3g93OZ 43 57 169 19 L9O 27
ffi-tE116T-4:-4;---T6çm_-FAAS.
M zaóóói 42 I t?3 5e rz¡ ?+
NGAIO DOI{NS____ ?392_A?_42__ 4 _L73 57 L27 28 GRANGE ROADTHAPUKU 2t36OL +2 le L73 4L 158 30
SA¡IYERS DOI{NS 233401 42 27 l?3 29 I3A ?1 KAIKOURA 234701
HAI{I{ER FOREST
---2860T- 47-s-t- TtZ m --zã¡Eõi
COiITIAY FLAT 23ó401 42 39 L?-f 27 101 24 t{A }tKS HOOD ?3ó302
RIYERSIDE ?2180t 42 43 t72 53 -IF---E----FERNIEÐ
548 ISLAND HILLS
sP01sH00D 23730L +2 45 L7t 18 I08 24
LAKËS STATION
Water & soil technical publication no. 20 (1982)
?2750L
22720L
42 25 tÌ,- 42 968
42 36 1?3 le
42 3e L73 20
42 45 172 ,7
42 46 L72 ló
r31 2?
t3,ô' 25

CULVERDEN
GME_E¡V---
2218A? 42 46 r72 61 +a 6 LOWRY HI_ILS STa¡_1s¡¡ 43q!-q!-!L-2L- 1?3 ó 75 L2
gÊ . evL
ãisaoi 4T5r 1E Í9- F- iL sÁL-uoRÃL-FoREsT zzï-tol ãis3o-1 Etsr1B i9- - --f 5- it - sÁL-H0RÃL-F0RESí- zzï-to7- 42 52 t r¿ 1> )+ r
PORÎ ROBINSON 2383a2 4? 5?- L73 18 ?8 13 MASON! FLAT zzes}L 42 54 L72 32 48 ó
¿2ô3V¿ -¿ )._ La2 !v
zzç4d1--12--55--T7Z-26---aZ-iT ARTHURS PASS STORE zresvz +z >6 I rr 5r ¿5v ¿5
?3e_Lgr_ 42_56 _r't! -2 ,-
171
T-l-? -ABr!-r-uLLqël-- -z-!22e,t--!41
t4 183 l?
--
SANDHURST PASS 3207a1 43 1 L72 42 ó0 lt
--r.t-otu-tt-¡-u 'hEKA --¡-e-ooor--11- T 173 5 79_ r'
HouHr rüHIrÊ srArIoN 31oeo1 I{A
-SRT_TÃSIN
1? 1 -111 ?9 ---FuTErÉTf
I P ARA
72A7A2 43 3 L1? 45 548
---9ll
3TT-7c'1 47 I 171 4ó f7 I
cRrfo¡eaunrr FoREST 311702 47 s 171 43 78 I !L'll3¡_Ë q4_L -E__ _ a?LZOL 43 9 tTz 12 7r tI
GLENÏHTRN È 311401 43 tl 171 21
nà ¡r-FER-n-TVE R -- -- -- 91 L2
A].IBÊRLEY
3 21701 43 9 l-tz +3 80 t7
Tõð-u-Fs¡--- 3?ø7õ67- 1-3 lZ -t72 2q- -- 1s-t2
-- :-lT4dT- 6-LT-I71|-2 s 7' lo
CKUKU 322!02 43 14 172 23 67 to
TEf,FO-SFSIATION
KTLt{ARNOCK
-
GLENALLEN 22960t 42 'e
l7z 39 51 I
ciËiñ'-- ttolaz- 43--2-a7T-+5--- -62 -6
CASTLÉ HILL 3r27AL 43 L4 171 43658
-FEIK_HIf,t
_=4ilg--f7T TTT4TT rT--_-TZ-T3------m-0-ur¡rTtRaãssE--------3T3-90T--E-5-TE-TirI- 56 a5s
RAN6¡ORA
t23502 47 le 112 34 66 9 I{OODEND ?23602 43 ?A 172 40 73 ló
L.COLERIDGE HOI{ES TEAD3l350T 43 ?I I71 35 óü7 LAKÊ colÉarocl 713502 43 22 l?l 32 ó1 6
TÃL-ËTHT¡RPE
- --3-13-t-07- -45 -Êfln-e
2A- 171-52 74 l0 wÉlu roresr- - 1z-+7ol +{-24 - 7.72-fr-------6T-T
¡IAII{AKARIRI BRIDGÊ 3246CIL 43 25 LlZ 79
ffi õñ- ---TtTTrJ r - -4t ZT
DARFIÉLD
!24IO2 4l 29 - -¡¡--Ça- 12 15 UPPER, LAKF TIFRON 314110 47 26 171 11 77 tO
---?E--e- - --frcV-Fl-¿ID-S--
L72 I 6.5
Ar¡1PORT 3Z+50L 43 29 172 12 51 7
43
SI{IRLEY 3256A3
-Þ-AFÃRIIÃ-TR-rSOñI-FARE - ã25-{OI - -43-tf
43 3ü L12 40 17 18
-
a7-f28
43
Èrpffi_¡R-rsoñr-F¡Rm -ã25-{oI --43-tr -a7-f28 - EREhHON 3058Ü1 31 170 5? e2 L2
iuoSfof e--.. - 5ó- 11 H0'ìE-RATA |.¡ËsT -3f58or 32 171 51 6-3---T
43
CHRISTCI{URCH 3256t1 +3 32 L72 V7 54 3 BRûFILEY
iI5-óoz tzt +r -
r C
+3
iuosrore---- II5-óOZ +z tl l?1 41 75 - r-{RI STCqURCI'{ 325103 3? 172 42 78 14
1 HoR0RÀTA
- 31i90i 13 L7l 54 ó5 '9
43
HORORATA SUB STATION 315e(i3 43 33 l?t 5e 51 5 WI GRAù{ AE RODc'0i'1E ? 25502 ?3 L72 33 544
I12 4a
HIGIJBANK PÛþ¡Ëì S1\¡. 3L57C2 47 35 17I +4
I,IOUNT PLEASANT 3251A4 43 34 T12 4A 53 543
B
172 GOIILEY H:AD LI\;HT. 325801 43 35 L1? 4g
HOR0TANE 3251A5 43 75 r72 42 71 15
.Eß-E. EltÊ-L-E-L D-S-r Lt t-it1С{-(- 3-r-ó7-QL -43 6 T5 18
? --lU- 4L-_ ó8 I
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--
3L6505 +3 76 -.-L7L_--3_-1- - - EÞ- - e-
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stRilHAH SEþlloE PLÂNT 3263AL 43 31 L17 19 55 9
üE-IHV-EN 1!ó6QL
-
- -43 38 -r?l--ae - -.-
7L L2
-Ë-Esg¿Ol¡tltÀ - --- 3.Ûé901-- 43 39- L79 5-4 tt L?
3 !6tù_? _ +? 19 _ Ll L 27-- __gt- r I
r,rouNT Po99E5!!-o¡L-- 3162C11 +3 32 L7-L- ]! -83 18
ST AVE L ËY
326401 47 ?9 172 28 54 ?
cneesloÈ 3lô8ol 4? 3e t'71 4e 86 t7
L INCOLN
puRAU 3?6'192---43 39 l7Z 45 L25 30 336001 43 4A 1?3 0 96 ?l
SPRINGBURN 3ló403 41 +l --
LTTTLE A(ALOA
171 29
EVAN9ALE -1113-03- 43 83 18 TÊ PIRITA TI{ÊAD 3ró901 43 4t 171 59 62 lO
42 rf I 20 _8/+,18 tI LYg¡iK_ 5T-AI I8N 3q_?J!1 43 _!3._ rla 84 13
- Water & soil technical publication no. 20 (1982)
"4
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æ
TATI
¡rouNT sor.tERS 7L740? 43 43 1?1 24
THE HERMITAGE,r1- -c-ooK3o?ro ll¡-++- Ito --- ó
KILLINCHY 3212A2 43 44 t72 L4
EASTHOODTLE FONS 3Ay 33710L 43 45 173 6
SOIfERToN 38992 43 46 tll s5
83 _U______ GRËENPARK__ 3275OL 43 43 L12 3L 453
zag 15 BUCCL EUGH r t¡tT. SOüE R S 317403 43 44 171 29 ?5 t3
5\ -l
TJH I lF RNfìK
3 1710 t 41 45 t?t tô ,A l,
lo0 21 BRAC(LEY, T.IAYFIELD tL73O4 43 +6 171 rrl 25
558
o \ AI-Ë-IÐUVÂUEIJ E l=L E -B¡ Y3eZ9-q!
- 43 46 L'tz 19
56 948
1?_l _35 _ óé _1_r
t{ I NCH tYtOR, S
318803 43 48 171 48 55 I
172 58 t37 27 LOCHA B ÉR
318001 41 5g 171 4 74 tO
171 l5 lI3 ?4 I,IAGNET BAY ___ .128701 43 5l L72 45 65 13
170 28 544 VA LETTA 3L85A2 43 53 171 75 58 I
AKAROA 32890L 4' 49
IrtouNT P EEL 3t5202 43 50
GÛDLEY PEAKSITEKAPO 3O84OI 4! 52
AKARoA HÊAD ____ 728eAZ 4? 57 t7z 59 -___ 8e _2r_ ___!{IDEAI_!!5HAßL __ _L,L?403 !3 54 t7r Z' 78 1?
ASHBURTON 319?01 +3 54 t7L 45 5e j_ __ DEEPBURN 3Oe8Ol 43 56 170 1?O 51_ e8 t5
ORARI GORGE 319206 +3 58 l7l t2 101 T8 BRAEI{AR
309201 43 59 170 12 6? 3
IqJryI- {OHN 30e4or 43 5e r?O 28 +2 4 HrltDs 3te4ot 43 5s 1?l 2ó ó3 7
171 ro sBrr ffi- ;ôó¿õi ¿í-í_jiffi
FORD 410601 44 7L ?6 58 6 HORIIELL s 4007a2 44 2 170 43 Ác å
HIIAST PASS 4eL3A2 44 6 L69 22 t+4
ffiñ+ç-la-
9
LAI4BROO( 4018û1 44 t?O 51 57 4
I t711e óO 7
CûLDSTREAT{ No.3 411503 44 9 l7l 33 ãl ,
.LAKE €IHAU_!_I¡rION +etBfJz +4
s l?l 37 5r t
LO- Lq 49 724 LAKE PUKAKJ NO.z _- 4OI1O2 44 11 17O B 12?
TEHGAIIA I 4O27O2 & 13 l7O t+4 51 7 1ËI,IUKA 4l?204 44 15 171 l? 453¿
iE--
ç9f!=CIEEK'r'lAllARo 403e03 44 l'8 l?0 54 ó8 12 TIIIARU AERoDRot{E 4l31ot 44 lB t?l 14 4? 3
SEADOIIN
RIEBOt{tlü)D __ 493801 44 22 169 51 60 + SilITHFIELD 4lt2o2 ¿* 22 171 15 4' 5
GLENITI RESERVOIR 414104 44 ?4 1.71 ll 51 4 TII{ARU HARBOUR 414202 * 24 171 l5 476
TIñARU 4t4ZOt 44 25 l?t 15 51 t ADAIR 4r4rol 44 26 fm
HAKA ITAKA uuhrNs DOIJNS 5lAlluN STATTON r+(xlóol 404óOl +4 44 26 r70 170 40 +9 3 r{ouNT NIt{RoD 4o4got 44 26 170 53 75 12
oTEXATATA 1062q3 +4 36 1?0 L2 38 3 __IIOANAROA 416101 ¿+4 36 l7t ó 78 l?
¡rA¡KORA 40ó?01 t4 40 l?o 41 ó6 6644 LAKE I{AITAKI
}|A¡HATE SADD-LE ¿07t-t-
40ô401 * 41 t7l) 170 2,
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47 I
1+ Ií7A
70 59 -----ã- 7 HArrrrATE
FORD HILLS 407?01 44 45
--- nzoói ++ +¿---Îtrt 57
70
46
Water & soil technical publication no. 20 (1982)

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ffi ,F----4ezz6z-44-Tr-rETt---18ç--ç---------tîrñÃmr-Eãy--
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TúEEñsfirFr s-õiioiffi----tr-i-ffi---Eirini
G¡BBSTO¡{ 5gggot 4, L68 57 51 7 CROI'IHELL 59O2Ol 45 2 L69 12 39 t
-mTÃK-ANút---- 5to5õ-1 +'s i " l_¿q-¡r-- - 5l -a - o¡¡r-n:: - E-çreor--€-T-a6r-?F------æ-T
--a --raE- 45_- - --4T-l - -RAN-Fu-RTf 50rt01 4, I 170 6 30t
-FTE-TFEER-
581?õi
tfAlPIAlA 501102 45 r01709?83
TË ANAU ÐOHNS 571802 45 ll 1ó7 50
59130r 45Tf-T-6e-TE 365 -- -_x¡T-æR
45
5oró01 45 11 1?0 4l t07 25 -t1ó02
11 l6e
GALLOHAY
59249L 45 13 ló9 79
28
HERBERT FOREsT
IIANORBURN DAlt
-TROTTEFS CRE'EK
TE AtìlAU
45
5-e25A2- 45 L1 T6E-2A- ---24-¿ w-Ãril¡Àîf
- -
- l6zÍdT' -85- r4--f To--E ,32
W ró915 59 ó
ËoRyEN HILLS 4eó501 44 a9 1ó9 30 58 I HILFORD SOUND 47ó901 44 4A L67 55 235 16
T[mm-FosT-EFFr-r-E---4-çzTõrîïEz-:toç:i---6=-7-=E
TTinRE----
-----ZõEE-oI - -44-TE -Fto ¡-o-- 4? -a----TARRAS--- 4e8401 44 ,o lóe 26 ,79
GLEìIORCHY 488301 44 5l ló8 23 78 15 DUNTROON 408601 44 52 170 4l 19 I
49930L 44 54 ló9 19 5ó 10 AL-AßSTONE HILL ¿r999ol ¿l+ )ö ló9 55 40+
TEX'õTGO_-
489801 44 51 169 50 49 3 KNOÐS FLAT _____489001 44 ló8 2 e07
IRROHTOIdN
'8 t?l 5 56 lO
Tf,YD-
KAURUTTHE DASHËR
-mFFSgCC-usF-
5T¿-762 --45 I5-- 1-7O 46 -' -9T-21
30 z
593601 45 22 169 76 t2 1 GLENDALE STATION 503401 45 22 L70 ?7 óo t3
5 03 EOZ - -4T -ZT-TZo--49---' -Tt - 11 ffiD--
574801 45 ?4 1ô7 53 öO E
5141$t 45 25 167 44 5t 5 TE ANAUr(A(APO RD 574802 45
- óî --6
25 ló? 4S 59 ?
-p-ÃEFÄII- --5o490T- -45-25 --L-ô,-e -17 - - RoxtuRdi{- Po-WER
-Sïñ;
-ss43õ-I--4-52Tl6119----=0-T-
-EYFF-CR-EF-K-
-5e546-1 4l3T- L-e,s zl - - 5-t--ó
G-R
-ÊÃ1 -rq
oS 5 -S w-A r'1Þ- - - 5958 0- t - 4-t-3-T--I69-49 ++,
GARTHIIYL?tlIDDLEt¡IARCH 5û5102 45 al 170 I 385 CFNTREWOOü 505?Ol 45 31 170 4ó 619
-5-E toT' -41-TT-Tæ-I9-_---- 1{-7- ---Hf LtTõ-Þ'' RorSnRcF-- '--595-405-aÆ- 33 169 24
ROXEURGH EAST
FlAflÃru\,^L TIANAPOURI
' --' ---__-
575601 4' 34 L67 36 51 5 MID I)OMÉ
585502 45 34 1ó8 30
-ëx-Ë-nn-v=rA-R-F;Þ-u¡Err1¡r -EOó-6Õz 11 1r -iz6 T'Ì- --tI -
6- LÕHÍHËR- 5-ft6401, -15-41- 16{21 42 3
-DEíp-TTRË¡EI-O;Z-_- 45 4r -I:ÇE 5e --- ]3
ruNROBIN '.q69Ú2 587101 45 44 168 7 5e
R f LÞEñ r\Io .I 5 912tL 45 4t I ¿i9 r 2 Lg
HINDON 1:ARM 5012itL 45 45 17û 12 62
I{ENDONSIDE 5877Ü1 45 46 158 4+ 41
9
7
êt
9
(,
Water & soil technical publication no. 20 (1982)
MUR{AV CRËEK
T? rl
3t
2Ö
I
3
4rc
5612OL - 45 42-- L6{TT------37--ThATKAIA
58?8ol 45 44 168 51 57 t2
pt,rt'w;¡o -
5o12t2 45 44 170 15 69 14-
ELAC(t{tLJiìi STATITJN 57871Û 45 +6 16? 4Û ?0 I
MüA trLAT' 5972ú? 45 46 1ó9 t7 41 3
5l
ât

N)
o
STATIoN NAr{gmLfï3---ffij
NUIIE ER
f.{ONOtlA I 5 7760 1
IAIAROA HEAD 5077Û1_-
ST PATRTCKS,DUNEOIN 588503
tÞ_
45
45
IULLIYAN__AAH 5_Q,95_o__3
INVERI{AYITAIERI 5083i1
41
45
47 L(r'| a7
-
4't tza 44 . _,
4e t68 32
1_9 _L7A _31__
51 1?0 22
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-NAf--TTrrlo¡¡
NUI{B ER
LAT. S LONG.E
55 5 L:: ËLAT 50?001 45 47 t7O Z 4L j
---19 -J. - -B4F-s- -J-!rN-EI-r-ç¡¡,t--._ ._ sea90l__.t.Js Jþ2__4_ 44 6
46 7 I{HARÊ FLAÎ 5í}84ùa i{ +ç tiO zd -1rr 2r
?? L6 _SAbI_YËRS 84Y 29góq1 45 !e_ IIO 3ó er 15
51 ó Rsss cRÊ=K roe¡oi ¿t 5a i70- 30 - 8-Ìi4
s B¡,rúo,r¡Lr eurnÃu 5alzo:- 45- il - Iio-It-- óo t2
BEAUIIONT
5eß402 45 52 foÞ ls
DUNEDTN BTL. GAR,pENS 5085C2 45 52 t10 3L 61 4
I{AHINERANGI DAII 59åi9ol 45 53
_-_ LTNHOPE
l¿ì9
__ 5S841O 45 53 L68 ?7
58 576
tE:M,t= I{ËTHER
I4r_ HI LL __ _____51 ee 0 l_ _!5__ 5 4 _ _ f_61 _ 57
souTH RSRVR.,DUNEÐIN 50 e4g2- -4t 54-- L-lc- i - X? --5 --3!8I[SI-DErQU|!ED-IN -- -- 5-qe1g1- +t-54 L7o 21
111 Zt r.tussÊL3uR6Hrt-lui,tÊtllN 509504 45 54.1?O 31 3t
LAITRENCE 5ee60t -1E ss - r¿s +1 si tZ--
KAHEKU 589óOt 45 tl tóg 40 4? 6
5ee2o1 -ã-ffiö-ä--r-ä-
LTNHUTE __ 5EB4IO 45 53 lóg 2Z 5g 6
CAPE SAUNDERS LIGHT. 5A8702 45Ñ
DUNEDIN A IRPORT
5úe2AL 4' 56 l?O ¡.2- 42
59eOt 7 16q
RANKLEBURN '
FOREST 599401 45
EtslE_eu._B_u_sll_
HENLEY _ 57_27ar
5oetot--tt -tC -_iro 58 169 26
_ qg, 5_9
to i{ n
_L67 46 46 5
Lf LLBURN
ô70óol 46 0 L67 40
-ttÃttOEvll-f-E--
546
680801 aeoßor -i* +6 0 n -r^o-Zó lo8 4e +ã couof a-nir-r--- ozo¿or-aó__l -
LOßA. STATION I
ó8050. ó80501 16? _ 4ó I tó8 33
n 627
6û 9
_ HA
REABY
rHOLA
DOI{NS jggo_a__4é ___Þ
6&0701 46 __
Z
l_r_?q 63 14
768 46 39 4 TUAPEKA f.IOUTH ó9Ü5OI 46 2 169
:ll5pF+icH'ra_L____ g!+!az_!q
73
3 Lþ7t3_
395
_2_c_ 8-
EAST L-oqL_Sc_tlqpL
GOR,5 6ß0903 46 __ _ __ó8qj_!_o_ 9þ _-4 I óg
5
29
1ó8
457
57 t7 t TA IER I f,4OUÎH ó00201 +6 5 170 L2 486
GoRE --
457
6E tO
503
¿sieor- ãe o--ioelð- ---E-T
__-_681701 46 Ióß_ 45 43 4
ó91e01 46 7 169 58 4g ?
ts z
gtQ!NS'UI-NI-0-N--
--_---é,-q!!10-- 4é---e-
PUYSEGUR POINT LIGHT.óó1601 46 i-_1ó6 --!6s 3?- 27 - 81 4
HTNTON oarãoã ?¿ -ó---r-oe 20- - -lo -l
3 orrrihli
OT AUTAU 681002 -ro +o tót-õ---- 40 2
P:åIE!=STCCK,T{An{ËRA s.6e¡5gl _19 !o róe 31 34 5 r{rNToN
IIII9I^
-Ð-_Ë_-ffi
é!¡æl-tå. rI
ó82810 46 ll -!é-8-2-g-----_{r
ü¡-ïÂuRA
1ó8 52 38 -¿
3
þ_ 68280l þ.1gllL _.rô _t_? L6g 52
cHRYSTALLS eEÁcH -9I?F4óìr-rãa
ó02101 + -:? 46 +-3- 12 -170 =!_ég -¿
Þe__. _ 3? _ E _ c_LrNroN _
37'
þ?¿?ez _1þ- 12 LqeL?-- 4? 6_
POURAKINO VALLEY 672elo 46 13 167 55 56 6
HEOGEHOPE 682501 46 t3 1ó8 a? 4L5
OlA}IUTI 6BZTOT- 4ó l4 l6s--to 36
B A LC LUTHA
44 4_._._PÊBBLY HILLS
45 7 OREPUK I
HOKONUI FI}RE ST
68250? 46 t3 168 35 392
6e27A2 46 t4 L69 45 --3t
2
68l6LZ tú I ó
6727û2 46 1?
683701 46 19 168 47
INCHCLUIHA _i!!_.3 óe38o2 jL6___rB __f_Þ? 50 _ 52 ?.. _- - _E_D_rN-qaL_E
333
Water & soil technical publication no. 20 (1982)

pAHIA 6?3801 46 Zú t61. 42- 54 5 SLOPËDOI{N -- , 693ZLA 46 20 ló9 LZ 42 4
rfËx-r-^rDÊR-_6ç4orõ-__=4;-7>-içÇ-ï- -- îi--1- - - _-
GNNtrrãrï¡r
- aal4ta- 4621--t6e n ----1î-t
INVERCARGILL AIRpoRT ôB43cp" 46 25 ré,q 2Cj- 36 2 !l\yËÀc,A3GI!!- ó843Û2 25 168 Z? 7e 3
ffi---6ñEdr--:4îæ-i;-¡t--Í.T'rr
--=õ4iEi- 46ffi
!,NA\,l Y ALLL I
LÊ A A
t¡tATAuRA I5LANDS óg4?10 46 z't lóg 45 4û 5 ot{AKA ó94{5û1 46 ?7 169 39 65 13
-{qr¡¡r
lluiqEl PgINI_ Lt9tlI: _ 6_?4?91_ 4þ_ CËNTRE ISLANIÌ LIGHT. ó74801 +6 28 ló7 51 45 5
-ÃI{ÀRUA-
?7 L69 49 ?)4
685301 46 3r
.ã¡¡äii-ilil-r-s---- ¿s5oof +e zz t6e 3 ---66
168 22 373
LT
BUCKINGHAM RESERVE 695ZIO 46 33 16e l? 7C r?
-oõ-e-fSf ¡Ho -nenf-t8ó4sr +a
-
-zs'
oan,r¡rsre¡lET--isLAND oeçror 46 54 1ó8 I 50 2
168 25 155
Water & soil technical publication no. 20 (1982)

APPENDIX E
Compadson of Regional Flood
Estimation Method with TM61
comparison because all catchments used here also were used
in deriving the regional method.
References
mates on average by 4t/0,
Table E'1 comparison of or estimatos with rM61 €stimates ($l and regional flood estimation estimates (efl.
Region
Number of
Catchments
Return
Period
T
roi/q)
Mean Std Max Min
Dev
(o+/q)
Mean Std Max Min
Dev
Canterbury/
Waitaki Basin 17 20t1, 2.11 1.19 6,01 1.10 1.06 0.36 1.A7 0.59
Westland
Northland
2011, 0.76 0.1 5 0.89 0.52 0.96 0.22 1.32 0.68
512) 0.56 0.18 0.88 0.38 o.94 0.23 1.16 0.60
Note: (1) Estimates of elo and Ozo from Ogle (1g7gl.
l2l Esrimates of Oi from Waugh fi 973).
122
Water & soil technical publication no. 20 (1982)

Appendix F
Flood frequency analysis for Otago and
Southland
F.1 lntroduction
At the time of developing the flood frequency curves for
the eight regions covering New Zealand, there were only six
relatively short flood records available for the
Otago/Southland region. This region's flood frequency
curve was therefore treated as provisional and was only extended
to the 100-year return period; for the other regions
the curves were drawn up to 200 years. The tentative nature
of the analysis is best illustrated by the fact that one of the
records used was for the Pomahaka River at Burkes Ford
(Station 75232) for the period 1963-1975. The flood peak
for 1972 of 1088 mtls was omitted because it appeared to
be an extreme outlier, yet this peak has been exceeded three
times over the period 1978-1980.
The number of notably large floods in the area in the
period 1978-1980, and the availability of substantially more
data, suggested that reassessment of flood frequencies in
this area was appropriate. This appendix gives the results
of the reassessment, which has been completed just in time
to be published as a supplement to the main study.
F.2 Data collection
With assistance of staff of the Otago and Southland Catchment
Boards, annual maximum flows for stations with at
least l0 years of reliable flow record were extracted. The
catchments are listed in Table F.l and their locations are
indicated in Figure F.l. The flood peak data are given in
Table F.2.
Additional historical data were sought. These data took
two forms. The first was estimates of large floods which
occurred before recording commenced and which were the
largest for a known period. For example, the estimated
p"it of 220 m3/s in tÈe Leith on 19-20 March 192í is the
largest known in this area since settlement, which is taken
as dating from 1850. The second form was when the largest
recorded flood was also the largest known peak in a
preceding interval. For example, the peak of 505 m',/s
recorded on the Makarewa River on 15 October 1978 is
known not to have been exceeded since 1895.
Sources of historical information are "Hydrology Annuals"
No. 3 No. 17 published by the Ministry of Works
(1955-1969), and
-
"Floods in New Zealand (1920-1953)"
published by the Soil Conservaton and Rivers Control
Council (1957), supplemented by information from catchment
boa¡ds and some early newspaper reports. As early
historical estimates are of uncertain accuracy, only data
considered to be reliable were used.
Annual maximum l2-hr duration lake inflows calculated
from records of levels and outflows (Gilbert 1978) for
Hawea, Wanaka, Wakatipu and Te Anau were used. Local
inflows to Manapouri were not used because they are
calculated as Manapouri outflow, minus inflow from Te
Anau, minus change in lake storage, and since inflow from
Te Anau is 6690 of Manapouri outflow the residual local
inflow is subject to large errors. Although the l2-hr maxima
inflows are less than instantaneous maxima, the
reasonable assumption that the instantaneous maxima are
a constant ratio (say 1.2) of the l2-hr maxima suggests
these data can usefully supplement the maxima recorded on
rivers for frequency analysis purposes.
Flow records were also derived for two contributing
areas in large catchments by subtracting, from downstream
flows, the upstream flows lagged to allow for time of
travel, Records of annual maxima were thus derived for the
Waiau River between Tuatapere and the Mararoa confluence,
and the Clutha River between Clyde and the
Shotover and the three lakes. Because these data are derived
by differencing hydrographs, after making assumptions
about the travel times of the upstream hydrograph, the errors
in the estimated peaks are significantly greater than for
other records. They were therefore not used in deriving the
regional curves; however, they provide a useful independent
check on the curves derived from the other data.
Table F.1 L¡st of catchments.
Number of
Stat¡on
Catchment number
in Fig. 1
Name of River and Recording Station
Year
Record
starts
Catchment
atea
(km2l
1
2
3
4
5
6
7
I I
10
11
12
13
14
15
16
17
18
19
20
21
22
73501
74308
74310
74314
74346
75259
75232
77504
77505
7A502
78607
78625
78633
78803
78906
75276
75253
23
24 84701
Water of Le¡th at University Footbridge
Taieri at Outram
Taier¡ at Sutton
Taieri at Patearoa-Paerau Bridge
Loganburn at Paerau
Fraser at Old Man Range
Pomahaka at Burkes Ford
Mataura at Gore
Mataura at Parawa
Waihopai at Kennington
Oreti at Lumsden
Otap¡ri at McBridges Bridge
Makarewa at Freezing Works Bridge
Middle Creek at Otahuti
Aparima at Dunrobin
Lake Wakatipu inflow
Lake Wanaka inflow
Lake Hawea inflow
Lake Te Anau inflow
Shotover at Bowens Peak
Manuherikia at Ophir
1 964
1 955
1 961
1 968
1 967
1 969
1 962
1 957
1 956
1 958
1 957
1 963
1 955
1 970
1 963
1927
1 930
1 931
1 926
1 968
197 1
Clutha tributaries above Clyde, and below
Shotover and the lake outflows (see McKerchar,
1981. Table 4.1) 1963
Waiau tributa¡ies above Tuatapere and below
Mararoa. {see McKerchar, 1981, Table 4.1} 1969
Cleddau at M¡lford 1964
45
4 705
3 066
738
150
122
1 924
3 465
766
152
1 160
108
1 040
27
215
3 133
2 624
1 384
3 124
1 088
2 036
3 839
2 336
155
Water & soil technical publication no. 20 (1982)
t23

Table F.2 Flood peak data.
NEW OTAGO DATA
NEW SOUTHTAND DATA
3I TE 73501
I.EI18 TT UTI9EESÍTY POOIBNIDG? sITE 15232
POitñtKÀ À1 Do¡t(zs ¡oBD
crrcHtBtT t8Et, 5Q Kü =
tollBER oP ÀXtltÀL PEÀKS =
IEIB PEÀI( IB¡I P¿TK
CÀrCllAIl IREÀ¡ 5Q Klt = 47A5
!0;8EF OF IIXûÀL PE¡ñS = 25
IEI! PETK IEÀE
45 ¡Àp RBFpREì¡cE = s16q:i63?2s
17 P¡iFIoD 0P REc, = 196q-e0
YETR PBTK YEÀR PET T
1964 4.7 1965 6. t 1966 1,\ 196? 5.2
1968 r 13 1969 8.5 1911. 39.6 1971 95. 6
1972 65. I 1973 8.5 1974 51.8 tq?5 ta?, 9
t976 46.7 1971 28.7 1978 49.4 19?9 23.5
t9B0 1 30
lBtf = 41.16 STD. DEv. = 39.9€ coEF. Op sKEs = 1.01Â
tolBs:
1. rflE t929 pElK, ESIltttTED tÎ 220 CUiECS, rtS THE LtRcESl
ST¡CE SETTLEI'EIIT À¡TD TÀKET IS ÎIIE LÀRGÈsT Tll TfE PERIOD
ts50-1980.
sIîB 7¡308
1955 10S5 1957
'1960 181 ¡961
1964 37.6 1965
1968 845 1969
1972 832 1973
I 9?6 t 43 1977
1980 2600
Pr¡[
2009
12't0
119
152
151
326
1ÀI8RI À1 OIITRÀñ
llÀP REPEREIICE = S163:9337q(¡
PERIoD 0P 8Ec. = 1955-F0
YEÂR PBÀK TEÀR PEÀI(
1958 425 1959 21Ã
1962 205 1963 368
1966 300 1961 19(
1970 266 t97t 43f
1914 864 19?5 J34
1978 1133 1919 r¡Oo
;!Àt = 593.2 STD. DEg. = 62t¡.5 Copp, Op SÍEc = 1.965
tolE5:
1. T_8!'l?qo-g_Err, rRE r868 pE¡t (Bslrt!llED À1 2179 coiEcsl
rfD ÎE?.1957 PEÀi ¡ERE IIKEI rS ÎIIE 1ÍRN8 L¡RGEST rìI
TI¡E PIRIOD 1858-1980.
5I1E 7q3 10
cllcfliliT À¡Er, sQ K; 3366
xltllBtg OP ¡¡[0ÀL pEÄis = t8
I'IR PgTf TEÀR PETK
1961 06¡t 1962 108
t966 56.6 1968 3OO
1971 115 1972 207
1975 96.2 1976 156
1979 96-2 1980 800
TIIERI tÎ S0110tl
lllP EEPEnEICE - s15¡t:939092
PeÂIOD oP REc, = t96l-90
TPÀR PETi t¿ÀR PEÀX
1963 t30 1e65 66.5
1969 59.4 r97o 76. !
1973 113 1974 311
1911 67,9 19?8 ¿ü?
t8¡¡ = 204.0 sTD, DEt. = 196.3 coEp. op siE3 = r.986
tolEs:
l. PB¡Ís, irssl¡c FoR 1964 rxD 196?.
cÀTCHllELT tREA, S0 Klt = 1924 ilP REPEREItCg 5711.221472
llullBEF oP Àf,tlûÀL PEI(S = tq PEnIoD oF R¡)c. = 1962-S0
IETR PEÀK fEÀR PETI( IEÀR PETß PI¡f
1962 1?6 1963 337 1964 96. I 'E¡¡ 1965 3lo
1966 216 1967 467 t968 516 1969 2¡9
't 970 2s5 1971 369 1972 t08? 1973 170
t 97q 206 1975 32A 1916 201 1917 375
t 978 1217 1979 352 1980 1210
ÍEltl = 435,2 STD. DEV. = 353.6 COPF. op SiE¡ = 1.?tO
ltotEs:
1. Tfir 1978, 1980 ÀXD t972 pEtKS íERE TlFEL tS TEE Î[tBr
LTRGPST TI THE PERTOD 1920-1980.
s rlE 17504 tlTl0Sl lT coRt
c^TcHiEtT rt8l, s0 ¡ü =
llUllBER OP IUtaUÀL PEÀRs =
IEIE PRIK
1 957 1 047
1962 586
1966 352
1970 252
197r¡ 21O
1 978 22f5
TETE PE¡(
1959 6CS
1963 tt33
1e61 656
19?1 443
t9?5 51C
1979 52t)
3q 65
23
766
25
llP REtEnutc? st70:013¡t3
PERIoD oP EEc. = 1957-S0
tEtR PEtß tzl¡ Pllf
1960 tt52 1961 35t
1964 260 1965 292
1968 1290 t969 62a
1912 121A 1973 2O1
1916 453 1971 1300
1980 1625
ËEtl¡ = 6c2.3 stD. DEI. = 520.3 coEp. op sf,B¡ = t.59o
ùtoTEs:
1. rflE 1978, 19t3 (1700 cu;Ecsl rrD t98o pErxs tB¡E î¡ßE¡
ls îfl¡ L^RGESÎ fIf TflE pFRTOD t870-1980,
srlE 77505
ctIcHllEN? ttEr, sQ ßÍ =
llUllEER 0P rXXuÀL PEÀKS =
PEIX IEIA
YDT R
1956
1950
t 961¡
t 960
197 2
1916
1 980
PETK
68 1957 !2\
rc,t 1961 92
117 1965 103
276 1969 259
214 1973 1 lC
165 1977 266
215
rrT¡str Àr P¡llt¡
ËtP REPEEE¡CE st5t:¡9t058
PEDIoD 0P REc. = 1956-80
IEIR PEÀÌ fBTÂ PIT¡
t95S rq3 1959 2tt5
1962 103 1963 55
1 966 106 1967 292
19 70 84 197t 2t¡
197tt 93 1e75 136
1978 590 t979 29t
iEtü = 190.¡ STD. DEV. = "124,0 CoEp. o¡ srEt = 1.638
SIlE 78501 ¡TIROPÀI TT ¡ETIII6IOI
SIÍI ?131¡ 1ÀIEtr tÎ PtTEtROI-P¡lt¡u cÀrcflllFl¡T ÀREt, SO till = 152 nlP REFERE¡cr
NUIBER O? = sl773t3t0¡5
ÀTI'OÀL PEÀKS = 19 PERIoD 0P REc, - t95B-77
c¡lcElt¡î rRElr SQ fr 738 iÀP BEPEfiEICI
tUiBEn OF À¡lott. pEtÍS = St45:675374
= l3 PEBIoD oP
IEIR
nEC.
PFTK TE¡ R PEÀß
= 1968-S0
IETR Pttf( tEtR
1958 Pttt
tt.6 1959 26,6 1961 2q.1 1962
IIIB PETf,
1953 31.3
2¡. t
IEIß PEÀi
t964
1t68 PEII
25.tt
61.0 '1969
IEIR PETI
196
IBAB
5 39,1
196? 1966 26.A
56,0 19?0
23. I 1968 t¡1,3
65. 6
1972
30.9 1971
1969 26.1 1970 25. O
¡02.r¡ 1913 q6.0
1971 17.7 7912 55. R
197¡a
1976
55,3
191
1975
3
68.5
19.8 1974 31. ó
39.0 1971 69,9
19?5
't
21.8 t9?6 30.7
51.
1980
978 t 37. 5
1917 ql.6
1979 I
205
Ëxlt{ = 28.93 SrD, DEc. = 1C.û2 COEP, op S(Et = 0.9960
iEl¡ = 76.07 SfD. DEt. = 47.67 COEP. oP SrEs = 1.98F
sITe 7860" OF¡:îI T1 LOËSDEI
s¡ ÎE 743¡6 LOGIXBoÀX tÎ PtERto
CÀTCflll¡ll1 àRP^¡ SQ ßñ = 116C FÃp fiEpFRENCE = SrSO:lBr¡g62
c¡lc8llrT rSEr¡ sQ l(r ùU;BEF = t50 llP REPERBICE
OP lIilûAL ÞEIKS = 22 PERIOD OF RDC. = 1957-80
¡0lBB¡ OF ¡lIÛÀL PBIÍS
= Stqtt:62¡t217
= t3 PEBIOD 0p nEc, = 1967-79 YEAR PfAK IFÀ8 PEÀK ÍNTR PRÀI( TEÀR PEI
II¡g ÞE¡Í IE¡8 PE¡R IEAR PEÀX TEÀR 666 1e58
f
1957
334
ÞIÀt(
1959 378 1960 271
t957 5.48 t968 20.7
't95|
t969 12.2 19?O 352 1962 352
22.9
1963 183 1964 211
19?r 35,5 1972 50.0 1973
196 5
21.7
-lc
197¡t 1 1q66 232
15.6
tc67 416 1968 352
t975 26.4 19?6 1s,7 1977
t969
20.3 t97B 211 l97C 21C
58.s
19'11 t69 1912 139
7yr9 1 8. 9
1 975 765 1976 453 '1917 871 1978 1171
197C 131 1980 I 10c
lBlf . 24.91 STD. DEt. = trt.92 COEp. oF SßEr = 1.2ge ñE¡tl È 454. I 51r\. DRv. = 29Ê. I coFF. oF s(Ft = t.27tt
Ìorts :
1. TBE 1980 pEti oF 365 CUTECS
NOTES 3
tÀS OñIÎTED FFOil TltE
ITTLISTS: I1 9Ts IT BITRETE oOT¡,IER 1. lIIF
ÀIID T¡tE IYÀrLIEL!
1C-8 ÀNTJ 198C PEIKS Y¡]FII ÌÀKE¡r ÀS lHf L¡RGEST I¡
LpxGTft ot ¡EcoRD ¡rs fùstrFFlcrEilT TO Rltt¡L8
THE PPFIOD
REÀLISTIC
1879-198i.
TETIIEI¡ PEBIOD 1O BB ISS¡GIIBD 10 Iî.
^ srtt 7a625 OlTÞIRT ÀT iCBRfDES BRIDGI
PRÀZEF
:l::__--- _ t::::
IT OLD ItTN R¡IIGF
c¡tc¡rrir tBEt, s0 [t = 180 ItP AEFEREIICE = S169:|t22516
c¡fcfitBlT rREr, SQ Kü !ûIBEB
= llÀP
ol
REF¡ll?Eilcr
¡IlûrL PEÀIS 5143:03't485
= 1B
122
PEAIOD OP REC. = 1963-80
XUÚBER OP TT¡Of,L PEÀKS = 12 PERIoD 0r 8EC. = 1969-80 r'¡¡ PEIf, TET¡ PEÀK IETS PPÀK fEtS PEIX
IE¡R PEÀT YEÀK PRTß 1965 31.2 1
TETR 1963 tt2.3 196¡
PEÀÍ
29.1
966
YEIF
30. 3
PEI f,
1969 23.4 1970 1911 t967
19,3
52,5 1968 85.5
11,9 1969 60.0 1970 70.3
1912
'19t3 22.3
1975 1971 43.5 1972 65.8
16.2 1973
1976
25.9
1
31. rl t974 tq.2
974
12.7
34.7
1971 11.9 1919 1915
1?,0 3q,2 1976 rt3.9
t978 88.
1977 90.2 1978 198
O
t980 26. 0
1979' 52.8 1980 r15
¡E¡i = 26.29 sTD. DEY. = 20,29 COFP, OF SÍF:C = 2,911 tE¡x = 61.3r¡ sÎD. DEÍ. = 41.93 COEP. oF SIEc = 2.28A
tu
Water & soil technical publication no. 20 (1982)
a

786 33
!lll::l- 1I-::TÏÏ-i:Î::
cltcElExl lRBl, sQ fl = tOlO rrP nBFEREtrcE : s1?7:331130
¡trlBB¡ oP lllûll. PEIRS = 24 PERIOD OP R¡c. = 195'80
tEA¡ P¡Àf fSÀB PEÀT tEÀR PETK IETR PBIÍ
1955 2rl 1957 175 1959 111 1960 216
1961 156 1962 169 1963 201 1964 90.6
1965 201 t965 81 1967 156 1968 395
1969 r78 19t0 170 1911 200 1912 263
1973 1l¡5 1974 136 19?5 195 1916 2\2
1977 318 1978 505 1919 287 1980 434
rr¡l = 223.0 sTD. DEv. = 103.0 coEF' ot sfEl = t'326
lolBs ¡
I. Tf,E 1978 T¡D'1980 PB¡TS CEIE TÀÍET ¡S lNE TUO LÀRGISÍ
III lEE PE¡IOD 1895.1980.
srrr 78803
:I:3ï-::::I-"-ilÏ1I
cttcErtrl tElr' sQ rl 27.4 ËÀP 8E?BR!¡cr s176:192268
llttDE¡ or rflÛrl. PE¡[s = 10 PER¡oD o! REc. = 1970-79
rllr Pltf tE¡B pBl[ IEIB PSTÍ IEI! PEÀT
1970 3.16 1971 9.51 '1972 13.41 1973 l.?3
19?¡ 1.55 1975 2.74 t9?6 3.60 1977 5. 1?
197ø 1.82 1919 9.40
;Elr = 5.ll STD. DEV. =
tl.O2 COE!. o! srEÍ = 1.170
¡PtEttt
lT D0¡RoBlll
IEIR PEÀI( IEIR PB¡K rElB PEIÍ ftlB Dltt
1930 1037 1931 1832 1932 1210 1933 t588
1934 1 106 1935 15rt0 193ó 1716 1937 llrt
1 938 952 1939 1080 1940 1293 19t1 17t2
1942 1889 t9¡t3 19rt3 t944 9¡r8 19t5 t93¡
't9q6 2265 19q7 1 160 1948 3227 19¡9 2l7t
1950 2867 l95t 975 1952 t¡459 t953 t5ó0
1954 1261 1955 1700 1956 960 1957 :¡11ó
t958 2022 1959 1255 't960 1 458 t961 1279
1962 2004 1963 A27 196¡ r 163 1963 1936
1966 1337 1967 30lr 196S 1854 1969 325a
t970 1512 197 1 1 t5C 1972 1127 1973 1706
1970 791,, 1975 2419 1976 t 104 1971 1169
t9?8 3991 1919 3¡23
ttEltl = 1829 sTD. DEV, = 841.9 coEt. Ol SiE¡ - 1.316
IOl9S:
1. TÍF II'PLOCS TERE DERTgED FÂOË [Àf¿ LEÍIL IID OOT'I.OI
BECORDS USrilc r l2-800R rrtE rtrEBVlL.
5ITE 9 I ?O LrÍE FtrEl rttlo¡
CÀTcllllELT à88Àr S0 fl = r38q nlP ¡Elgnzlcr =
ùUtlBER 0F l¡il0ll PEIKS = lt8 PEBIoD 0t nEc. .
IETE P?TK
193t 187
1935 653
I 93e 606
19q¡ 599
t 947 !rt2
1951 502
t955 619
1959 367
196:t 338
1967 903
1971 325
1915 q6 t
fETR
1932
193 6
19¡t0
t 9ll¡
19C8
1952
t 956
1960
196¡r
1968
1912
197 C
PB¡K
593
503
599
332
845
157
371
561¡
453
¡r08
552
365
IE¡ R
1 933
19 3?
l94t
1945
1949
't9 53
1937
19 61
1 965
1959
1 973
1917
l93l-78
PEtß rBtt p;lf
539 193¡t 717
l¡23 1936 60¡
585 l9e2 62t
540 19¡ó 926
665 1950 7¡¡
605 195¡ 373
700 1958 556
$15 1962 839
ø23 t966 631
1 r 36 1970 650
cl?CElBIÎ rlsr, SQ Ír 215 llP rErrBBtc! s159:119827
rulBlB O? I¡IU¡L Ptrfs = t8 PEEIoD ol ¡Ec. = 1963-80
162 197¡t {36
rB¡¡ PEIÍ IET¡ PEIf, IEIB PETf, tEtn Pllf
t23 19?8 ltl¡
1963 15.2 1964 1îs 1965 t43 1966 81
1967 l7q 1968 131 1969 6 t. 6 t 970 10.2 ËEtù = 596.5 srD. DEv. = 197.5 coEP. oF sßP9 ' 0.7392
1 971 6 1, 6 1972 8l¡.5 1973 11 1970 68
t975 135 1976 t03 1977 169 rs76 53q ¡OTES :
19?9 119 1980 196
T. TflE IIPLOflS 3ENE DERIYED FßOI LTßE LEVFL IID OTîILO¡
NECORDS USTf,G À 12-HO¡IR 1I'IE IIITESYTL.
rEtI = 126.5 STD. DEt' = 113.7 CO!F. oP SKEI = 2.895
fotlS !
srlE 957C
LÀr(E îE t¡lt lltlot
1. tEE '1978 PttÍ CÀS Ttf,E[ tS tllE LlnCEsr rx rtlE PEFToD
1914-1980.
CtrCtËEf,T tREl, SO K¡ 3124 ülP BEFEREICE =
l¡UliBEF OP ¡[iÛll PEÀxs = 5q PERIOD OP REc. = 1926-19
NEW SOUTH ISLAND WEST COAST
YEÀR PEIK
PEÀK
PEÀf, YEIR P'Tf
1926 1q20 'EÀF 1921 1737 'EAR 1928 20 r6 1929 1500
srlB
9 1 l0
Llt(E fltrlllP0 IftloS 1930 1500 1931 1285 1932 2511 1933 2604
193ft 2365 1935 1609 1936 2608 193? 1¡20
1938 l8lq 1939 260'Ì 1940 3499 194'1 2294
cÀTCBllFxT ÀREt' sQ KË = 3133 llÀP REPERE¡CE =
1942 1362 l9rrl 1935 194r¡ 20 rB 1905 2540
NUiBER OF ¡xNUlL PEÀKS = 53 PEBIoD oF FEC' '
1946 3C6l 'l9tt1 221 ''
t9rr8 3¡a59 19¡9 1948
1927-79 1950 2167 1951 2671 1952 lt4r¡ 1953 2865
YEIR PEIK Y¡ÃF PEÀ¡( TDIR PETR f!I¡'B PEIT 195¡1 2942 1955 2C6C 1956 210U 1957 3512
1927 1¡¡9t 192A 1855 1929 1?9lr 1930
r 958 31105 1959 2¡t88 1960 2818 1961 1937
75¡
1931 1250 1932 929
t962 tB80 1963 1166 1
1933 792 193¡ l26t
964 1723 1965 227e
1935 199 1936 736 1937 648 1938 r061 1966 l6rrl 1967 3715 1968 2381 1969 2552
1919 512 1940 1q90 19¡.1 1635 1942
1970 226A 1971 2202 1912 2220 r9?3 1495
10tt6
1943 939 1944 669
1974 19¡¡4 lq15 2426 19?6 20 19
1945 1332 t9¡6 2799
191't 2009
1907 1288 l9q8 2118 1949 1866 1950 1463 1978 4839 19fs 4r¡38
1 95f 1 094 1952 26qA 1953 11r¡5 19511 10?3
1955 1C26 1956 759 19 57 2933 1958 20r5 ËElN = 2561.8 sÎD. DFv' = ?68. O COEF. OP sKE¡ = 0.9820
1959 890 1960 1181 t961 1700 1962 It98
1961 585 1964 t057 '1965 963 1966 t t¡2 l¡0TEs:
1961 2CUi 1968 1869 1969 2254 1970 88r I. T8E INFI,O9S TE¡T DERI9ED ¡ROII LIÍE LPVgL AIID OOTPLOT
r9?1 780 1912 1\29 1973 812 197¡ loTt
RECOFDS ÛSIIIG À 12-IIOUR TIIIE I¡lERVAL.
1975 2006 1916 1 138 1917 1 469 l97S 2¡60
1979 26J2
;Eltl = 1382 sTD. DEY. = 609.2 coBP. oF s(E¡ = 0.88{9 sIrD 75276
saofoÍE8 tT BosElrs ÞErl
l¡oTEs - I
i. rue rt¡Lots IBRE DERTSED FRoË LÀiE rtYEL ¡lD ooTrlo¡ C¡lCErErT tREf,' SQ ß; = lC88 irp ¡EPlBEfcE = s132:589786
RECOBDS OSII¡G T 12-HOUR TIIE IXIENYTL.
TUTBER O! llf,tttl, PEIIS = 12 PERIOD oF REC. = 1968-?9
IETB PEÀK IEIB PETK IETR PETI tEÀR PEÀÍ
639
srtB 9150
LltrE Clllfl I¡FLOI 1968 l¡51 1969
1970 369 191 1 328
1972 00r¡ 1973 277 197¡a 528 1915 56c
1976 r¡? 1 1911 508 1978 c18 1979 tt81
cllcflüE¡Î ÀnEl, S0 Kll
I'IP RE?EREf,CE =
PERIOD OP REC. =
167.5 COEP. O? SKEi = l.l¡06
IOIBER O! I¡IIUÀL = 2624
PEIÍS =50 r93O-?9 rEl¡ = 4C5.C SrD. DEY. r
Water & soil technical publication no. 20 (1982)
125

F.3 Analysis and results
tatively placed with
Region on the basis
the hydrograph for
to the Taieri River
Paerau and Loganburn at Paerau (Figure F. l0)
Southland rivers (Figure F.9).
-
than the
(see section 3.1.6). Plots with similar shape were overlaid to
form combined plots.
Flood frequency data thus plotted were found to lie in
three groups:
(a) peak lake inflows and Shotover floods;
(b) Southland floods and the pomahaka floods;
(c) East Otago floods.
Group (a) closely resembled the South Island West Coast
data
Canterbury data
(see
these two groups
were
I plots of the data
they
Support for the differentiation of the lake inflows and
Shotover from the other sites studied is also given by the
hydrographs (Figure F.8). These show that floods are frequent
and occur at the same time for each catchment. Since
the floods result from the same storms, it is an argument
for each catchment having a similar shape in its flo;d frequency
curve and for grouping them together. Also shown
in Figure F.8 is the hydrograph for Cieddau at Milford.
Finally,
-
the hydrographs (Figures F.8, F.9 F.lO) show
that the majority of large floods in the decade l97l-19g0
o-ccurred in the years 1978-1980. Figures for F.g, F.9, F.l0
also show the wide extent of the October l97g flood which
was the largest of the decade for many of the records.
F.4 Gonclusion
and the Manuherikia at Ophir (1971-1980) wirh rhe
regional clrves (Figure F.7) shows the difficulty in determining
which curve is appropriate. Central Otágo is ten_
graphs (Figures F.8, F.9, F.l0)
because the frequency of minor
ach region but not across region
ïable F.3 Co-ordinates fiom regional frequency curves.
O2.33/O
o5/o
olo/o
ozdo
o5o/o
orodo
ozoo/o
S.l. West
Coast
1.OO
1.24
1.45
1.64
1.89
2.O8
2.27
Southland
1.03
1.46
1.82
2.16
2.61
2.94
3.27
sth
Canterbury-
Otago
0.97
1.51
1.99
2.48
3.17
3.73
4.33
Acknowledgements
D. McMillan in compiling the
Miss K. Vollebregt in anatysing
owledged.
References
Fitzharris, B.B.; Stewart, D; Harrison, W. l9g0: Contribution
of snowmelt to the October l97g flood of the
Pomahaka and Fraser Rivers, Otago. Journal o!
Hydrologlt (NZ) I9(2): 84-93.
Gilbert, D.J. 1978: Calculating lake inflow. Journal o!
Hydrologlt (NZ) I 7(I): 3943.
Ministry of Works: Hydrology Annual. (No. 3, 1955 ...
No. 17, 1969). Ministry of Works, Wellington.
t2Á Water & soil technical publication no. 20 (1982)

c o
E
an^in
o
\'
f¡l
U)
o
oô
^' s' r-
: ô¡
f¡¡
o _ L \-zi
,-l"-l'X
\/'\
þ
-:
t!
.E .c,
o
F
.=
Itoø
= o6
at,
| ; -r'-9-\-/
-l¿-ì
.'
^,2
.t ì.---.'{ ---
t!--/
\-'
-r'---\-,-.
" --b-.^,
r\- -ti
ffi r
:' =

ét
êt
REOUCEO VßFIHTE
2. 33 5 l0 ?0 50 t00 ?Do
NETURN
PEFIOD (TERRSI
Fþurc F.2 Plot of normalised flood frequency data for lake inflows and Shotover River superimposed on the Wost Coast data given in
Figure 3.13' (Circled points are lake inflows and Shotover floods with plotting position retuin peiiod greãt€rthan 20 years.l
o
o
REDUCEO
VNBIHTE I
?.33 5 ¡0 20 s0 too 20D
RETUB}'I PEBIOO (YEflRS)
Fþure F.3 Plot of normal¡sed flood frequency data for the Pomahaka River and the southland R¡vers.
t?ß
Water & soil technical publication no. 20 (1982)

ct
ct
o
ê
o
.25
ñEDUCEO VRBIFTE
2.33 5 t0 20 50
RETUBN PERIOD (YERRSI
100 200
Figuo F.4 Plot of normalised flood frequency data for East Otago rivers (Taieri catchment and Leith) superimposed on the South Canterbury
data given in Figure 3.1 5. (Circled points are Taier¡ catchment and Leith floods with plotting pos¡tion retum period of greater than 20
years.)
Qr/Q
\q
\þ)
X
y'x*
o
0 r.011 2.33 5 ]0 20 50 100 200
RETURN PERIOD 1 (yrS)
Frgurc F.5 Average points from Figures F,2 (ol, Figure F.3 {x) and Figure F.4 ( +). The fitred curves ars for (a} West Coast, (b) Southland,
(cl Sor¡th Canteôury-Otago.
Water & soil technical publication no. 20 (1982)
t29

SOLITH
I
EA
l')
COAST
soUTH CANTERBURY/oreco
SOUTHLAND r l00km .
E$r. F.6 Regions inferod from dots of flood frequency data.
130
Water & soil technical publication no. 20 (1982)

RETURN PERIOD T (Yrs)
20
Figure F.7 Frequency analysis of annual maxima derived for Clutha river tributar¡es above Clyde and below Shotover and the lakes, (x)
1963-198O, Manuherikia (ol 1971-80, and Waiau Riv6r tr¡butar¡es above Tuatapere and below Mararoa (tr) 1969-1980. Regional frequency
curves are also shown.
I
sHotovtx . uuxtils PK i3/5
t
cLE00Êu o Ë¡LFoRo sÛuNo il3/s
LÊfiE HNKÂÍIPO INFLOH Í3lS
Figurc F.8 Hydrographs of shotover, cleddau and l¡ke wakatipu inflow, 1 971 - 1 979.
Water & soil technical publication no. 20 (1982)
t3l

0tiftflt a itÉitut5 ü¡. il/5
tg?t
t9?¿
l9 ?J
i¡fÊ¡Erâ nI FflEEZtrc lis 88. ff3/5
¡l
f
Flgure F.9 Hydrographs of two stations ¡n ü€ Soúhland region, l97l-l9gO.
lfflti¡ Hr f(ltHH0H-PHtffHU iJ/5
I
l06PxBU8N nr PFESFU ¡3/S
,å
P-
t8{uHE8lÍtF Êt oPttfi t9/5
t
lt?r lr?{ tE?! ¡9?6 ¡9?7 t¡76
Fþure F.1O Hydrographs of three Orago stations, I9Zl-I9gO.
a,
\* 1; lr' P. D. llulbe¡¡ CoUu¡at Prlala, Wcllia¡oo, Nd ?Fl.d-lSll
Water & soil technical publication no. 20 (1982)
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