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Model paraEete! C tras r:egressed on three catchnent characleris tics , slope, length and area, for aLl the fourteen catchnent_s useil for paraneter optimlaation. The regression analyslg showed tiat sLope ls the &ost lDpoltan! factor, and th.t the corlelalton with tengt_h tras Bore signlficant than rlth area. ttre best equatton based on foulteen catchDents ls: c = o.o75 staPE- '297 rENc.rB'176 (s.18) where SLOPE ls the average slope(C) average length (b) of the catcbnent. of the catchbent, and LENGTH is the The dultiple correLalion coefflclent for the equatlon is O.69 (nultiple determinatXon coefficlent 0.46). F19u!e 22 deDonstrates t]re foro of tiis relatlonship. Independent catchnents Equation {5,18) was useil for predictlng the lDodel-Palameter c for the four lndependent catchnents. ttre c_values tius obtafuted nay be sumarised as follcllrs: Catch4ent 301 2052 4276 4471 Predi"cted c ,i2 .o77 .094 t f' t' I I t t t Slope (c) Length {!r) I o.5 2.O 3.3 t.9 30. o 8.6 ro.1 I ttle resufts of these slDulations are 'lealt with ln Section 5'8' t 5.7 Moalel 5: Tj'De of Entry cene"dl desc?iPtiorl The tlme of entry nodel is represente'l by Figure 23' Essentialfy' -it is a tine-area !;uting net-trod in lthich the increase in area l'ith tilie is ltnear, anit the tine for the full alea to contribute is denoted tne ttltre of entrY (1E). To alerive the iolet hydlograph the rainfalf excess is appffea t3 tle ttroe atea aliaglam. rf, as is assume'l he!e' the tlne .r"u'il.gt* ls llnea!, the eff,ect i5 t}le sane as a noving avetage of the ratnfall- excess trtien over t{me 1E. Such a nodel is very sfu0ple to use anal 1s lncorpolateal In several exLstlng design plocedures with perhaps t-he best knoun belng the TRRL !'tet-hod {watkins' 1962)' I t I I I I I I
I I I I I I I I I t I I I I t I t I I t I roo I t a : SenBitivit! of aodel pat@rete" ?E FIGURE 23 RepreseFtrtlon of time of entry nodel As r{1th t}re ot}t€r nodelE, t.lr6 flrat inv€atlqation coocahed the eerBltlvlty of th€ p!;aneter(s) - ln this listance, Tt. slnce the tloe of entry rnodel 1s a one PAratleter Bodel, the values of the obJective functlons can be plotted allrectly agalnat tE. Ftgure 24 shoss the plot of tJle obJectlve functlons ISE and PEAK for EIx coEblneit errents on catchDetrt 2061.. It is apparent that altfiough the PEIX functlon ls [o!e 6.ns1tlv6 thln the ISE functlon, both Bhor{ a Dlnlduro value at th€ aase tE valua. th16 ia an encouraglng slgn th.t the best valu€ of IE ha5 bacn obtrlneal, trEtlcularly aLnce the sdt'e aesult {as obtaltreal for the t:rro otJrer catcho€nta testad (3Il rnal 4177). 16 15 >r3 ro c.tchmGnr 2o€1 ro tt t2 TE(.nin) Figule 24 EugEeBt€ that the rbestr value of fE ls of the orde! of 1l-12 Dlnut€a, a Duch high6! value than the 2-4 olDutea usually aalopt€d ln tleEl,gn practlc6. Trble L5 thors t}le tE values obtaineal fo! optlnizatlon on i.ndlvldual ev€neB for. all of the test catchEents. Again the ,best' valueg of lE ale quLte latge, Doat belng ln t}€ ranqe 7-l.O El.aut€s. Ot}Iei polnta to not€ fId the tabl6 ale that t-h€ co€fflclent of varlatlon of lE irith ev€nta 1s leaaonably 1on, {nd thrt catchlent 4175 again'ploalucea an rnoualous lesult. t3 / / t5 t6 FIGI]RT 24 Sensitivity of time of entry paraneter
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