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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />RAIN STORM <br />MONTROSE <br /> <br />Downtown Montrose waS <br />virtually turned into a <br />river Tucsd~y nt 3:30 <br />p.m. ~'hcn a hea\>)' rain <br />andhnilstormstruck <br />without warning...water <br />wasronningoownthe <br />streets, overflowing <br />eurhsandrushingdown <br />the lower part of Main <br />Street. <br />South Townsend Avenue <br />looked like the Uncompo.h- <br />gre River for a time as <br />runoffwaterrusheddow'Tl <br />the full length of the <br />str~et and then rushod <br />west down ~!ain St reeL.. <br />Catchbasins at the east <br />sideoftheintersc<.:tion <br />of Main and Uncompahgre <br />wore clogged with trash, <br />causingujaketoform <br />acr-.JSS theoati,c street <br />after the storm. <br /> <br />I <br />I <br /> <br />SLASHES <br />AREA <br /> <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />_ 17 _ <br /> <br />HYDROLOGY <br /> <br />Pea.kDisCharqeS <br />Flood discharges for the I1l<ljor drainageways in this report were obtained <br />from a report CampI cted in April. 1979 by Hydro-Triad, ltd" (R~f~rence 1). <br /> <br />The Uncompahgre Valley <br />Water U$er~ A~sociation <br />reported precipitation a~ <br />I. 06 illche~. This appeared <br />to bl' the heavie~t amount <br />of 11lOistLlre in one day in <br />June for over 46 years... <br />The storm sl'emed to cOme <br />in from the ~'I'st or south- <br />west and head cast and <br />cil"cll' nrolmd to the north. <br />The Loutsenhizer Canal <br />which runs in back of Flat <br />Top had broken, and water <br />carriedaboutafootof,ilt <br />over one 12 acre plot of <br />sugarheets and ruined the <br />~'~ole fi"ld. <br /> <br />As a part of that previous study, runoff hydrographs were devploped using <br />the Soil Conservation Service procedure for the sub-Oasins. The hydro graphs <br />were then combined using Muskingum routing to yield discharges for Montrose <br />Arroyo, Cedar Creek and Dry Cedar Creek. <br />Ditch crossings in the study basin, with the exception of the South <br />Canal,wereanalyzed by assuming them to be flowing full at times of flood <br />such that tributary runoff would flow across unimpeded. The South Canal, <br />because of its 1arge capacity and safe operating record was assumed to <br />collect runoff draining directly into it and convey it out of the basin. <br />The impact of snowmelt runoff was evaluated and determined to be <br />significant only for thehi~~erfrequenc.y events. The discMrges in Table <br />5 include the effects of rainfall and snowmelt runoff. <br /> <br />6-2).67 <br /> <br />Urb~drology <br />As part of the previous study, peak discharges were determined for <br />each of the local urban Sub-basins. These discharges were calculated <br /> <br />using the rational formula and rainfall data kept by the National Weather <br /> <br />Service. (Reference 3) and the Uncompahgre Valley ~ater Users Association, <br /> <br />{Reference4}. <br />The peak discharges cal culat~d for the 10c<l1 urbdn ar~<lS w~re routed <br />and combined by Gingery Associates to determine the effect of urba ndrain- <br />age on thestlJdy streams. The individual urban sub-basins were combined <br />by lagging the hydro graphs of upper basins to account for travel time to <br />the lower areas, then adding the hydrographs. The results are su~arized <br />in Table 6. It should be noted that the urban rlJnoff isof short duration <br /> <br />andwi11 have subsided before the upstream peak flows reach the city. <br /> <br />-16- <br />