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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