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Flood History 8cc/luseofchannollmproveroonts/lndconstructlonofCherryCreek O:Ilm, many of the flood problems that once loomed large along that stream have been elTmlnated. Runoff from .the upper b/lsln is completely controlled by the dam <lnd flood control releases are limited to tne there was considerable damage upstream from the dam. Prior to the existence of the dam, maJor floods occurred on Cherry Creek Tn 1664, 1876,1885,1912, 1933,and 1935. Nlnemajorfloodshaveoccur'red In the Sand and Toll Gate Creek basins since 1896. No flood dischar'ges are available for floods In 1896,1912,1917,1921, 1933, and 1938. On 30 May 1948 a localized thunderstorm dropped 8 Inches of ralnandhaTI In four' hours on the lo",er basin of S<lnd and Toil G<lteCreeks. Floodlngresulteddo",n- stream of Colfax Avenue. Estlm<lteddischargesonSandCr'eekof 7,720 c.f.s. and 10,500 c.t.s., respectively, at Colfax Avenue and /It the mouth caused overbank stages tr'om 4 to 8 feet deep. Tourist cabins near Colfax Avenue and <In 011 refinery near the mouth were damages, but farms and livestock feed lots In the flood pla1n suf- feredthelOOst. On 8 and 9 May 1957, intense rains occurred over Toll Gate Creok and the middle Sand Creek basin. The rains began about II P.M. on B May and Tal I ~te Creek crested at 3:30 A.M. On 9 May at Colfax Avenue. The estimated peak discharge on Toll Gate Creek was IO,500c.f.S. 211' 6th Avenue, while 25,500c.1.s. was estimated for Sand Creek at Yosemite Street. At 6th Street the f/lst rising flood crest exceeded the cap/lcity of the culverts and overflo"'edtheroadw/lY. Water flowing up to 1.6 fe"t deep washed out the r(Xld oed. Extonslve dOm<lgcs \oIore Inti Tcted on homes, uti I T- tles,andbridgos. A woman and two children were drowned Ineb<lse- mentep<lrtmentbyToIIGateCreekflood",aters. Keavytotorrentlal ralnlall occurred over the Sand <Ind Toll Gate Creek basins on 16 Juno 1965. Rainfall averaged 2 to 4 Inches over the Sand Creek basin. Toll Gate Creek flowwasestlrnated to be 17,000 c.f.s. at 6th Avenue and Sand Cr<lek downstr~m from Tol I Gate Creek was estimated to be 18.900 c.f.s. Nearlv everv bridge crossing the creeks was damaged or destroyed. The flooding caused extensive d<lmages In the Aurora vicinity. The downstream 6 miles of Toll Gate Creek overflowed from 300 to 1,000 feet ",Ide; the down- strea", IOmllesof Sand Creok flooded 5001'0 1,500 feet wide. Obstructions to Flood FlOws Where many bulld1ngs, walls, or other structures exist On the flood plain, the overbank flows during large floods are obstructed and water surfaces are raised. The study reach on Cherry Creek IS highly urbanized; Sand Creek and Toll Gate Creek flood plains are much less so. The degree of development Is discussed elsewhere in thlsrepert. Channel constr'lctions due to or'ldges and drop str'uctures Impede stream flows during large floods. In the Cherry Creek study roach there are 38 street and railroad bridges; on Sand Creek thero are 17 bridges in the study reach; on TOil Gate Creek there are 5 bridges. There are numerous drop structures on all the study reaches, many Installed to control channel eros10n. Toll Gate Creek passes through culver'ts at 6th Street that restrict large floods causing overflow on the stroet. The rel/ltlonshlp of wator surface profiles of large floods to str'uctures on the stream Is shown by the profiles on plates 2 through 7. Plant growth In tho channols at var10us po1nts adds to channel roughness and Impedasflows. Sornaofthechannel retaining walls on Cherry Creek from Goldsmith Gulch to the mouth are being undercut by erosion and could collapse during a major flood and obstruct channel flows. ca~acity of the down~t~ea~ channel. Our!ns the evening and night o' 16 June 1965, the Cherry Creek Reservoir Impounded a flood which had a peak Inflow of 58,000 c.l.s. The flood storod in the reservoTr s<lved an estimated $130 million In flood damages downstr'e<lm fr<:rn tM d/lmon theCherryCr..ek/lnd SOUfhPI<ltteR.Tver flood plains. flowever, 9 10