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52
aletetuine:
{1) whether lt was bett€r to estbate ep fron S €ural then ? f!onr
P
Qp, o! altrrnatlvel,y to atttrat. Tp !a(0 I |'d tr@
%
(i1) t-he effect of catcho€nt 4175, anal
(ilt) ttle eff,€ct of, trsitrg preallcted rathe! than obBelved Q- o!
T- in tie lntehal reLatiooshlps,
graphs of 9_ predicted against Q^ observed and T- predicted agalnst T-
PPvv
observed were plepaled. these shoited that t-he 13 catchnent equallonE
gave better correlatiotr coefflclents of Preaucled on observ€al values
even l{hen catchnent 41?6 eas lncluded. lhey also shoted tllat predlctlng
Q -oPfroe
S gave ure hlghest corlelation on 9- observed, but ttle low€r
c;rleLatj.on of Tp Pretlicted on Tp obselved' rt itas therefole decid€d
ro predict Tp frJn s by equatlon (6) and 9p froo Tp by equation (5'25) '
Each equatlon givl.nq a corlelatlon
of 0.65 (note tnis is of siBllar
co€f,fic1ent
order to that
of Pledlcted on observed
obca]neil flcm estlDatlng
both O and T
_tnese
frcm s) '
Using eq,.r.tion", unlt hydlog.aPhs \,ete estlDate'l for tfie f,our
t'est catchnenas, anal each of the test events was eldulated' Table 22
gives a suDDary of the objectlve erlor frulctlons' cotoparj'son of these
;esults nith tfre ottrer surface routing nodtels shoes that the urllt
f,ya.oqt.ptt detioil as ilevelopeal here perforned far r,,orse than-any of the
o_th.r-rooaett, partlcuLarly with leqald t'o peak estisatlon' lhls
inalicates soroethlng is wrong itlti the analysts, since botlt th€ the of
.na th€ Nash cascatle modlels ar6 effectlv€Iy uni! hydrograph oodels '
""aw tne if.ne of ently ooalel glving a lectangular unlt hydloqraph and t}le Nash
cascaale givlng a sDooth curveal unlt hyikogtaPh' It t'toul't be-exPecte'l'
aft.r.f..", thit a trrangurar unlt hydloglaph nodel i'ould vield reEufts
lnterroeallate bet{een t}rese othe! tvo. hde€d, lf a trlangula! unlt
frya.ogr.pn Doalel hail been lflcludea ln t]te Package tiis plobably eoutd
tt""" 1."" the case. lloweve!, It l.tae onty aleclded to aPploxlrdale tne
catcbment avelage unit hydloglaPh by a tliangle at a late stage' so the
lriangular unit hydrograph \tas not conslaler€al ea!l'le!' rhe leason ithv
thj.s latter nodel has alone so baallY 16 explalned th€refore by the lalge
nuober of events that had to be rejected fron the catchDent averaglng
process (fo! t}re other riodels each event Produc€d a lesponse even lf tie
itt was not very good), anal atso by the long tlEe lntervat of the ilata
ln relation to unlt hyalrograPh tire to peat - cault1ng very unstable
indi.vldual unit hyilrogralths.
5.Io Non-Ilnearitv of the sulface loutinq procegs
It' nas declateal to lnvestlgate the non-linearliy of the ratnfall-runoff
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