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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)
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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
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Preface Water & soil technical publ
Page 9 and 10:
annual flood Q (the mean of the ann
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Water & soil technical publication
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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: I ++ ++ * E 4.6 Analysis of North l
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
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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
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ét êt REOUCEO VßFIHTE 2. 33 5 l0
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SOLITH I EA l') COAST soUTH CANTERB
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Water & soil technical publication
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