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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)
Page 1 and 2: WATER & SOIL TECHNICAL PUBLICATION
Page 3 and 4: Regional flood est¡mat¡on in New
Page 5 and 6: Tables 1.1 Risk ofexceedence for sp
Page 7 and 8: Preface Water & soil technical publ
Page 9: annual flood Q (the mean of the ann
Page 13 and 14: Doto ovoiloble on TIDEDA Figure 2'1
Page 15 and 16: P=45 O= 15 x4 (l) '= o o t.25 2'.O
Page 17 and 18: Êv2 ( ko) Reduced Voriote y I'O t1
Page 19 and 20: turn period. A plotting position fo
Page 21 and 22: 'o ,l\, I zl l- I Water & soil tech
Page 23 and 24: Table 3.2 Flow stat¡ons used. SITE
Page 25 and 26: e process of examining the simtrend
Page 27 and 28: Iì_ t_ I I I I I I I t-. I I tñ I
Page 29 and 30: Þ I"IEST COFST 0 o I E 6o o o 25 3
Page 31 and 32: SOUTHEBN REDUCEO Y VRBIßTE NETURN
Page 33 and 34: SOUTH ISLFND HEST COFST I]ÊTR èo
Page 35 and 36: SOUTH CÊNTERBURY DRTÊ NEOUCEO Y V
Page 37 and 38: COMB I NED ,,IE5T CORST DRTR o rt
Page 39 and 40: BÊY OF PLENTY DRTF o o o NEOUCEO Y
Page 41 and 42: NOBTH ISLRND ßEGIONÊL CUBVES 1.50
Page 43 and 44: data for this area are required bef
Page 45 and 46: NELSON REGIONFL CURVE BEOUCEO Y VRR
Page 47 and 48: 46 EÊSTEFìN NEI,,I ZEFLÊND DÊTI
Page 49 and 50: Table 3.9 The grouping and the grou
Page 51 and 52: allowing curves rather than just st
Page 53 and 54: 3.5.5 Extension method The NERC (19
Page 55 and 56: Table 4.1 South lsland catchment ch
Page 57 and 58: I 2 t l¡ 5 5 7 I 9 l0 t1 ,12 I5 1{
Page 59 and 60: decided instead to use estimates of
Page 61 and 62:
\Í l{ I t, ìj( Fþurc 4.4 Distrib
Page 63 and 64:
62 Fþurc 4,6 Logarithmic rcsidual
Page 65 and 66:
Table 4.6 Final equations for South
Page 67 and 68:
I ++ ++ * E 4.6 Analysis of North l
Page 69 and 70:
Non Pumice = õ = 3-24xto'6 AREA'7
Page 71 and 72:
Northlond f C"ro^ondel f Eost Cope
Page 73 and 74:
Table 4.11 Comparable equations for
Page 75 and 76:
Poo led cv Pooled o.40 F¡guro 4.12
Page 77 and 78:
mates of Cp typically range between
Page 79 and 80:
-J æ 'll o Eo !¡ Assemble llood p
Page 81 and 82:
Year 1958 1959 1960 l96r t962 1963
Page 83 and 84:
The estimate of Q from the regional
Page 85 and 86:
Water & soil technical publication
Page 87 and 88:
Maguiness, J.A.; Blackwood, P.L.; B
Page 89 and 90:
The liequency factor K is a functio
Page 91 and 92:
e.9., Linsley et ol. (1915); lrish
Page 93 and 94:
Maguiness, J.A.; Blackwood, P.L.; B
Page 95 and 96:
sltt 930 t [rûltRÀict ¡ l? s;¡t
Page 97 and 98:
3950't flrlÀRt R tr îlt¡Ît ;tP
Page 99 and 100:
S ITI 29202 RuNttiltcl I ¡t tllEtt
Page 101 and 102:
ïI-'_____ ::19: lt¡IPt0r n À1 i
Page 103 and 104:
9100r GNE? R ¡T DOBSO| s¡18 93207
Page 105 and 106:
6800 1 sBlrri R tT SrITEC¡,tttS 6I
Page 107 and 108:
APPENDIX C Summary of tho data for
Page 109 and 110:
oæ ON LAT. STATION NA ATION LAT. N
Page 111 and 112:
o NUI,IBER HHAKAIIARU 854801 38 L7'
Page 113 and 114:
l9 AT NU¡IB ËR AR',tËtlANA ÂRAI
Page 115 and 116:
A ON LAT. STATION NA NUMBER AHUNA 5
Page 117 and 118:
â NUI,IBER Lü{G.E ON NU14EER I,IU
Page 119 and 120:
æ TATI ¡rouNT sor.tERS 7L740? 43
Page 121 and 122:
N) o STATIoN NAr{gmLfï3---ffij NUI
Page 123 and 124:
APPENDIX E Compadson of Regional Fl
Page 125 and 126:
Table F.2 Flood peak data. NEW OTAG
Page 127 and 128:
F.3 Analysis and results tatively p
Page 129 and 130:
ét êt REOUCEO VßFIHTE 2. 33 5 l0
Page 131 and 132:
SOLITH I EA l') COAST soUTH CANTERB
Page 133 and 134:
0tiftflt a itÉitut5 ü¡. il/5 tg?
Page 135:
Water & soil technical publication
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