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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)
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WATER & SOIL TECHNICAL PUBLICATION
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Regional flood est¡mat¡on in New
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Tables 1.1 Risk ofexceedence for sp
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Preface Water & soil technical publ
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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
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P=45 O= 15 x4 (l) '= o o t.25 2'.O
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Table 3.2 Flow stat¡ons used. SITE
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e process of examining the simtrend
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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: Year 1958 1959 1960 l96r t962 1963
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
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