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, Dbstructions to floodfla~ The eff~ct af obstru~tio~~ dua to bridges and their appro~ch fills h~s been described in previous peregr~phs. In the vicinity of the Lo~all Avenue bridge, brush and other debris dU~P6d in th~ floadway would obstr~ct the cha~nel locally ~~d, during ~ major flood, ~auld seriously clog bridge wate:way op~n~ ing" downstream of this area, th~reby sub5tanti~11y Increesing flood depths. The sanitary fill in tha vicinity of 18th 5tr~et is ~n ob9t:u~tion th~t would also increase the depth of flo~. Addition~lly. landfill that hae been pl~csd downstrse~ of the Denver end Rio Gr~nde Western R~ilroad bridge perti~lly blecks ths west ends of the 11th Street bridge ~nd the Denver and Rio Gr~nde Railroad bridge. In effeot, this blookage contributes to the depth of flo~ or heed loss of the fututs flood. as shown on the ~ater surface profiles by reducing the flood-carrying oapaoity cf the channel. i Da~ show th~t the ~ost sev~re flood-prod~cing .torms havs ooourred during the late s~ring or su~msr ~onths. Much of the tot~l precip- itation at the higher elevaticns is in the form of snow. R~noff fro~ this sno~ often aug~ented by general precipitation. is ct a ~axim~m in the late spring and eariy su~mer months. In ths plains region, most of the precipitation is in ths fo.m of rainfall ~hich occurs during violent thunderstor~s at irregular intervals. These storms and the phy3ical features of the ~atershed Can produoe the rapid concentration cf runoff that characterizes fla.h fLoods of high peak flo~3, small volumes, and short durations. v"tOCit1M Along the Wild Hor~s-Dry Creek study reach, velocities ~uring th~ JUf'B 1921 flood evereg~d 12.8 feet p~r eecond (8.7 mil~s per hour) aocording to the USGS WDter-Supply Paper 487, "The Arkaneas .~iver Flood of June 3_5. 1921." Flood Records There are no record~ of stream stages or di~charges available for Wild Horse-Dry Crsek ~hich derive froD gaging 3teHons maintained on the str!la~ channel. '~ithout ,""eh duto. tha rate of riae and duretion of past floods cannot be accurately , , , , fiooded Are~e. Fiood Profilee. and Cross Sections Pl~tes J through 5 sho~ the approximete arees along Wi.d Horse_Dry Creek th~t would be inundated by the Standard Project flonn end the lntp.rmedtete Regional flood. The actu~l iimite of these overflow eraas on the ground may vary .lightly fro~ tho~e shown on the map becauas the lO-foot oontour intervai and , , , i deter<oined. Information on past floods in the sree, ~s available in ns~sp8par fila3 and other historic~l document~. is al~ost ox- clusively concerned ",ith th.. l"rger espect~ of flooding on tho Arkene"s River Or fountoin Creek. The flood profiles and flooded from tha reeulte of previous studios, o~~!e cf t~~ m~ ~o not permit ~te~ise plotting of the flOOded fi..ld mape were d~velopod investigations, and ar.."boundories. Platse 8 and 9 show the high water profiles for the St~ndard Project and Tntermediate Regional floods. Accurate eS- timates of '~at<n surface clavations ''''Y bc o..hined fr"", the"e areas office computetions. pletee. flood Ocourrences Analy~ls of cli~atologicel data and revle~ of the flood history for the Arkansss Ri~"r subbasin above John Martin Plale 12 5ho~s two orOoe .sction. that a.e t~ical of the 10 ssctions obtained on Wild Koree-Dry Cr,,~k in tho roa~h investigated. The locations of ell gection~ are eho~n on t~e above tef~r"nced plates, ae ~"l. aa the Bl~vation8 and ~.t~nt of overflow of the ~t~ndard Project flood ~nd lntsr",adi"t~ P.agi<.",d flood. 2D a