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Cror,s-soction data and tooogran~ic ma~ninry ~avino a contour interval of 2 feet Cind a seal e of I ,. ~ 400 feet were established by rhoto<yammotriemethods from fliohtsmado in April 1975, Thr:.se dat" were lurniSh<J{j by the Urban Orainaqe "nd Flood Gontrol District, incoo:>eration with the Golora10 Wat'lr Conservation Eloard, DouglasCounty,andllraoahoeCnunty. U, $, Goolo~ical Survey 7.5 minute quadrangle maps with 10 and 20 loot contour intervalsata Scale of 1 inch e'luals Z,OOO teet were also used in the study. Bridge and roadway survey data were pro- vidod by the ColoradO Water Consr:.rvation Board. FACTORS AFFECTING FLOODING AND ITS I~PACT Obstructions to Iloodllows - TherO are seven roadways which cross tho Cherry Creek llood plain described in this rerort. Arapahoe Road and Colorado State Hiqhway 86 present the largest potential for obstructlnq floodtlows. The Cherry Creek basin is located within an area whiCh is prone ro rocoluing v~rv intense rainlal I sometimes 01 cloud- burst magnitude, Floods have resulted Irorn storms covering lar"e areaS receiving heavy general rainfall osweli asfromstorr1S covorin(ls'mll aroa5hutproducingextr~lyinf"nserllinfall. Floods qenercllly occur in th>:! period fro", 'hy thrQu'lh ^"T.Jst, Annual p~ak diSCharq"s in t~e study reach, however, MVll ~",on r"corded trom Februilry throuilh 5ellt"",~"r. M;)nmadeobjects, slIchasbuildings, cars, and fences, as well as trees, brush, and other veqe~ation located on the t lood plain can also cause flow obstructions. These items, while r8~ln- Ing In place, not only tend to create hiqher stages on the llood plain becauso ot reducod Ilow area and flow blocka~ but may also create higher localized velocities as tho II00d waters flow around them, Ifthn I loodf lows are of sullicientmagnitudetodlslodge those flow obstructions, llood staoes may lower in that localized area. The debris may then lodge at locations farther downstream, thus compounding problems, Thisfloatinqaehrlscormmnly lodges against brldqe pIers and bridge decks; the flow area is thon reduced or t~e channe I I s completely blocked. T~e blocbgn can pro{juca sevare stage and valocity increases, often accomoanied hy ~ridqe damage or complete failure. FLOOD SEASON IIND FLOOD CHAR~CTERISTICS The up land ,1r"a5 'n tne Cherry Creek oasi n con I",.n d.~- sectnd topographic r1) I i..f wi th ste"'p Str<:1il'" slcn"~. ~ I <'>Ods are c~~racterizad by rapid rises, hlo~ ~axi~um di5ChargA5, short <luratlons,andcomoaratlvelv lowvolumcsoftofdl runoff, Major flood crests <:Iener;) II y pdS5 Ir"", t~e upstream to the down~trc1ll"l arailswithinJperiodofbetween6t08hours, FloodO<1"ksfrom thundBrstorm~ coverinq smali areas arc raoidly attenuafed by Icoehactsnave, nisrorically,notooon"prOhlemon Cherry Cree~, Ica jams, however, could occur in the future although th1) chance ot occurrence of StiCh a nhAnomP.nan is quite remote, valloystoraqe. Flooddamilgereductionm<!ilsur"s-Thep05sibllltyof luturellooJda"'a<1es in the lIpperChorry Creek area has been ~mn~hat reducod by the construction 0; 32 floo~water retarding structure::>. The Soil Conservation $ervice cnmolcted construction 01 th"s" strucbrC5 In 1065 iI', part of ~n overilll nlan i1S pre- 5"r.tod In two wilt"r,hf\d work Dliln~" TMso nlans wure the " "