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<br />. <br /> <br />ANAI.YSIS OF TilE CAUSES ANI} T1(IGGEIHNG EVENTS <br />OF mSASTIWUS TORIU:NT 111.001) <br /> <br />by Milivojc IIrajkovic Dipl.Eng.' <br /> <br />Zoran (iavrilovic Dipl.Eng. <br /> <br />AUSTI{ACT <br /> <br />A disastrous torrent Ilood on the Vlasina River of 26 June 1988 was of un. <br />prcccdctUcd inlcnsity in Yugoslavia. The catchment area am...-ctcd by the cal;lstruphc <br />cacd more almn 1000 km~ and the damage was estimated to one billion c..Iollilrs <br />I hl)SC rcsuhs indicated u need to find dillcrcnt anafylkal approach because, besides <br />visible tnlces, the actual records of nood were sparse. Rain gauging stations in the <br />zone alleelcd most seriously were completely destroyed as well as w.ller level <br />gauges. Since the torrent l100d computations on the base of 1100d traces arc nul <br />reliable. Ihe causes of lloud occurrence and dcvclopmcnI or l100d itself had to he <br />reconslrucled. <br /> <br />I. INTROIHICTION <br />The Vlaslna River calchment area is 985 km2 large, al 1300-1700 m a,s,l. Thc <br />t:unflucncc of the Vlasina and Juzna Mon.IVa River is al 250 III iI.S.l. This SlhlW~ Ih:ll <br />Ihe Vlasina and its tributaries flow i1t a sleel) slope which is one uf the basic prercqui- <br />sites of lurn:nl flow. The catchment is of fan-like geomctry which is ChanlClcl istic liu <br />Imrcnt flows 1.\ the atlcrnoon ofthllt day, the upstream pall of the Vlasillil c:uchlllcnl <br />covering JOO luul, was slricken by an intensivc ) hour (ainnlU The movement (If <br />cloudburst was convenient for formation of numerous torrent l1110ds 011 lrihulilril" <br />which jointly limued disastrous WHcnl 11001.1, lirst on large tributaries and lht'n, on lhe <br />Vlasina itself. <br />At the very beginning oflhe lidd investigations, it WilS Ihund dun only Ol1l~ l:lill <br />~auging station existed iii the center of the zone aneCled by cloudburst, which rc- <br />cUliled the precil)italion I'8te 01'220 nun l'Or two hours nfintensive rainfall. The uthel <br />stlltiul\s were destroycd. There werc also several adja~ellt stations but Iheir rccords or <br />noud were nol s3tistactmy so thai radar data on cloudburst movemenl had to he all". <br />lyzed in order to gel real picture of its development 11\ spiu:e and time. (Ref. I.) <br /> <br />~ ~1i-li~~;J~-I~mj~~)Vic l)ipl.l~nt:..lnslitute fur the I)cvcl(lrm~ut of Wall: I' RCSII~rl'l's <br />Jilnl~lilV {crlll ,jilwslava ('CIIUlg KO, 11223 IlcugnuJ(lkh I)llluk) Yugl)slavm <br /> <br />114" <br /> <br />I <br />. <br /> <br />YUGOSI.AVIA FUK)J)- ~^N^I.YSIS <br /> <br />. <br /> <br />11-11 <br /> <br />" In ll~al respect, meteorology - rudar surveys were used for reconslruction of <br />fClll~lilll~ USlIlg lh,esc data, as well as those oblained by lorrent bed survey, by <br />gram, SIZ~ lln:lIysls ,1I1d by dClermination of peak flood on some tributaries and along <br />the river liSCH, the nond could .be analyzed. This flood has been presenled in detail in' <br />olher papers so thai only essential excerpts will be given here (Ref I). <br />F~oods at large rivers with organized monitoring of hydrological siluation and <br />regular discharge measurements arc generated and lasl tor days, while 10rrcllti.11 llows <br />Onods arc generated and p.ISS in few hours. <br />o Such waves are usually formed on small tributaries ofa lurge river now i.e. on <br />~IS subw;:tler~hcds. The tormalion of the Oood wave and the consequences it p;oduees <br />111 the down~lream, part of Ihe main Oow depend on Ihe number of its tributaries <br />(subw;:uersheds) aOected by lhe rains of heavy intcnsity. <br />, Flo~d walers discharge measuring is nOI possible during the peak of a toerell- <br />II~I Oood slIIce, abundant sedimenl is being transported through the water logethcr <br />wlll~ other stull (w?od, parts of destroyed structures, cars. CIC.). The only lcasihle is <br />S~lrl.l~C Willer velOCity measurement but the experts should be al Ihe spot since this liq- <br />lIId Iluxlure could be so ll1usl~y that it is sometimes called Ot "muddy stune flow", These <br />fhet ilrc very oncn neglectcd 111 hydrologic and hydraulic calculations. <br />This is why numerous parameter methods for nood walers calculations under <br />1 ~IC comht iuns of insutlicienl measured and observed values have been develoJled <br />sll1~e tll~ me~ho~ls b~sel~ on, the s.urvf..')' of flood water traces, river bed geomctry and <br />scdllnCIll gnulI size dlSwbutlon ,give unreliable and onen illugical results, <br />Sin<.:e the meh..'Q- <br />rological situalion above <br />the aflcctcd watershcd had <br />been registered and l()I- <br />lowed by meleomlogical <br />radar's, the results confirm <br />(,,' 0 the basic postulates and <br />~ procedures of the devel- <br />oped computing melhods <br />I fCfNIl ~ of applied in Ihis case The <br />... Cil y developed and applied <br />C) ClolldblJrsl shadow melhodology poinls onl <br />Ift\ Poinl where Ihat the one storm could <br />\:1 discharqc arc produce dillerent flood dis- <br />calculolca or meosured charges, all depending on <br />o sC'1o (km) ?o the cloud movement direc- <br />~_==.=---~=-=- I ______~___ tion and its discharge <br />- -- fOcus. <br />Fig I. The Vlasina river w:ilcrshed (siluation on 26.06.1988.) <br /> <br />,'. ., This is whr ~ spe~ial atte~lion has been paid to the precipitalion regime unaly- <br />SIS. .1 he ~haractefl~tlc~ oltorrenllal floods is a large quantity of precipitation. The in- <br />tcnslly oj these rams IS nol unilonn, on the contrary it is extremely ununifonn with <br />mauy brakes. (Fig. I ) <br /> <br /> <br />- <br />