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<br />IIYI>R^lIl.1(' ENCilNEERINO 'I)'"
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<br />2. ~.LOOl)WAV~;ANALYSIS
<br />A detailed OOtId traces investigation and data collection were carried out aHer
<br />the flood. The attempts to reconstruct lhe flood wave ilnd 10 ci.ltcululc the nmxinunll
<br />discharge on the basis ofthc poor dilla remaining aOcr a wrrcnliul flood using dassicill
<br />methods have not given reliable results. As 10 the mentioned river Vlasina Ilood. the
<br />use {;r classical methods for the flood wave n....construction has given a very high ll1axi~
<br />mum discharge with lhe unproportionally small runon' cnp.u..ity_ According In the ob-
<br />tained v.llues. the runolT cocllicicnt has had a value lower than unnualmcan Villuc {II'
<br />the runon' cocllicicnt. The flood wave rcconslnlctiol1 has been pcrlhrmcd using the
<br />l1Iodilicd sYlllhetic unit hydrograph method developed in the Jaroslav Cerni In~tilutc
<br />for the Development of Water Resources. The method has been developed on the ha-
<br />sis of the classical SCS mcthod
<br />OilTerently from the originul, Ihe modified method docs not h,lVe the lag linn-
<br />as a walershcd constant, but the rain duration function. The modi lied fi:Jnnula fill 1 Ill'
<br />maximum wave and discharge calculation of the triangle shape, hus the followlIlg
<br />shape:
<br />O.5(,,"'~I'f!
<br />{!..I.I\ = (kll)~I'o.(uttl ')"11
<br />
<br />( I) where: Q.....~ - maximum discharge (m'/s)
<br />I' - watershed area (km1) 1\, - ellcclivc precipitalion
<br />tk . time of precipitation duration
<br />k- relation betwecn the watershed retardation and concentration
<br />tn - hydrograph increase time is calculated using the ref form
<br />a - watershed shape and sile parameter is determined according
<br />to the nomograph a:=tlF) rer.l.
<br />When using this form, a speciill attention has been paid to the rain which
<br />caused the nood The natural wave lorm is calculated using the filllowing form.
<br />Ot"I{f"Alll()_ (2) where: ,
<br />Q _ compulation lime discharge (t) 0...... - maximum hydrogmph ordmatc
<br />AI- parameter representing the relation between the retllulalion time (T,)
<br />and wave concentration time (T r>. This parameter is determined using the
<br />funclion: A"I\T,rr,)
<br />O. parameter reprcscnling the relation between the time I and T" (o'=fl.trr" ~t).Rcf2
<br />Considering thai the rain duration time, in the case of the Vlasinn river Ilood,
<br />had been recorded by the ohservers at lhe destroyed gauging sla~ions as ~cll ~s hy, the
<br />inhabitants, a mathematical model which divides the whole ram durallon llIue 11110
<br />short periods, has been applied. The design precipitation duration time for each ana-
<br />lyzed watershed has been computed using the model (author Brajkovic) which Ims the
<br />following form:
<br />(ll=.l<.ot" (3) where:
<br />Pt - rainfall of allY duralion Ku . cllaractcristic unit intensity
<br />t - rainfall time (t>O) a - regional parameler (0<(1.< I)
<br />The parameter ex depends on regional climate characteristics and is defined by a stalis-
<br />tical analysis urthe registered precipitation. Fig.2.
<br />The characteristic unit intensity (KlI ) represents the ratio of the tolal rainfall nnd Ihe
<br />total (real) rainfall duration time, i.c.:
<br />K 0 ::; ~ (J) where: Pu - total rainfall
<br />'.
<br />
<br />tu - real rainfall duration time (excluding
<br />Ihe signilicant brakes)
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<br />Y\I(;OSI.AVIA H.OOI~.ANAI.YSIS
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<br />1J..:;ir,lIl"lIi"r.,1I dUfUlil1ll lillII' in 1111'1
<br />. 1"~"...,'I""' _"."",,,,,,,,, . ? ,..,......
<br />..:r VI>..IM""~ ,.".ft."" .. { """'n..~ .~,.II.""""'c.
<br />. !. \"0'''''' ....rh~'~", . ~ "..,"'.~,... ~...~.. ""'0'
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<br />ft.U
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<br />The rainfclll is calculall'tl lIsing thc
<br />giVl'11 formulae for .1IIy duration time,
<br />in one point. Ilowever, in the form
<br />(I) average Ilrecipilatiol1 of a WiI-
<br />lcrshed arc used,The correclion fac-
<br />tor (ell) is delefmil1l'd 011 the bilsis or
<br />sllcciaUy Ilrcpnrcd I!.tllnogn1llhs
<br />cre,lIed in Ihe .I;:noslav ('nni Insti-
<br />tute. 'p~I\F) ReO.
<br />F' ~ Il'ducliunal watershed
<br />area is the sllrl1lce of the circle drawn
<br />around the wiltelshed
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<br />Fig.2. Rainfall Thickncss and durain ratio
<br />The enectivc precipitation (Pe) is delcnnined from the total precipitation (1'1)
<br />by using the known SCS method form:
<br />p/., (I'..02d)' 1(1'.' O.8d) (4) where:
<br />Pr - cnectivc mnolT layer I'\I-Iolal precipitation
<br />d - soil humidity deliciency (mnon" preconditions)
<br />By using the form~ 1-4, the entirc watershed characteristics (main now and the
<br />tributaries network), and the earlier created nomographs. calculated are, the maximum
<br />dischitrge, wave shi1r~ and the characteristic precipitation for all tributaries as well as
<br />their occurrence probability. The enclosed table shows computation results for impor-
<br />tant walershcds.
<br />
<br />The aim of mentioned computations and analyses rcprcsents the
<br />reconstruction of Ihe Ilood genc!\is
<br />along the now and over the wa-
<br />tershed up to the moulh. The com-
<br />putations presented here have
<br />shown much better concordance
<br />with the traces of the flood, meteo-
<br />rological radar data and the real
<br />Ilood discharge duration time (on
<br />the basis or the numerous witness
<br />statements), than lhe computations
<br />performed using classical methods.
<br />}:igurc (.1) shows lhe
<br />waves at the oUllet profiles com-
<br />puted using lhe precipitation data
<br />and reconslmcted using hydraulic
<br />formulae. The dincrenccs arc
<br />obvious.
<br />
<br />l~cconst.ruclcrl nnd recorded
<br />!.!.O{)~ .waves aUE~oJnls_
<br />C I Ylasina (nwd.llJhllwnil.byd.)
<br />- @Lu2nica(mod.$ynlh.unil.hyd.)
<br />-- (i)Y1asina (mod.SJ'nlh.unil.hld.)
<br />. Y1a~ina (mod.llJnlh.unil.hyd,)
<br />, Vlnsinfl (mod.S)'nlh.unil.hJd.)
<br />@Ylasina(dasielreeonslrlJCl.)
<br />.- @)Rr.cordcd nood nve AI. (6)
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<br />Fig.). the waves atlhe outlet prolilcs
<br />The table presenls parallel values of irnllOrlant wave characlcrislics (calculated
<br />using the Plccipitation dall!, the Mallning-Chczy fOl"l11ula and the time IL'COrded hy the
<br />observers.
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