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<br />I <br /> <br />I <br />I <br />I <br />I <br />I <br />[ <br />I <br /> <br />'-5 <br /> <br />prOfiles <br />Profiles <br /> <br />O~age Estimates. Damage estimates were made for the 10-year, 50-year awl <br />lOO-year storms d'isuming ultimate flow conditions and existing channel and <br />floodplain configurations. Thes!' diUllage estimates provide the tlaseline <br />a<:jainst whiCh to evaluate thp.benefits associated with alterndtiveflood <br />improvement plans. In evaluating damages, the following general criteria <br />should be observed: <br /> <br />Floodplain Dl!terminations. Io'at!!rsurface <br />Corps of Englneers HEC-2 c{)IIlputerrnodel. <br />following criteria: <br /> <br />calculated <br />determined <br /> <br />using <br />using <br /> <br />'" <br />the <br /> <br />are <br />'" <br /> <br />a) Peak discharges as noted should be used to determine water surfac e <br />profiles. <br /> <br />b) The (loodw<ly in Denver should be determined assuming equal en_ <br />croaChment int~ the exBting floodplain which rl!sults in a 1 foot <br />rise in the energy grade line elevations. <br /> <br />a) Residential andcorrmercial damages are to be based on actual pro- <br />pertyvalues and curves developed by the Flood Insurance Adminis_ <br />tration and the Corps of Engineers. <br /> <br />c) Friction between cross sections ShOUld be calculated hy averaging <br />the friction slopes at each section. <br /> <br />b) Agricultural damages are to be based on informationobhined from <br />Soil Conservation Service. <br /> <br />d} <br /> <br />c) Other damage estimates will be based on the total reconstruction <br />cost. <br /> <br />A contraction coefficient of O.1<1ndexpansioncoefficientofO.3 <br />should be used unless special factors warrant modification, such <br />as defined in the HEG-2 Users Manual. <br /> <br />Bridge Freeboard. All proposed bridges crossing the South Platte River <br />shOUld maintain a minimum two-foot freeboard between the lowest elevation <br /><)f the bridge, or attaChed utl1itypipes, and the lOO-yNr f100d "ater sur- <br />face elevation. <br /> <br />p) <br /> <br />Thl' HEC-? "red al h,. ;rlgp rout i ne ~hn"l 0 bp IJwcI for ~ 1 1 bri ogps. <br /> <br />'} <br /> <br />A factor of 1.65 should be used for total loss calculations in the <br />HFC.?'llOof'l. This is theeq1Jivalent of c = O.R in the orifice <br />flo..equation. <br /> <br />Channel Des ign: Sand Creek to Basel i n~ Road. For pl anni ng and ~e~ ign of <br />thf' Snuth Pl atte River in Ada'll; County (Sand Creek to Ba~e 1 i ne Road) the <br />following channel :k'iign criteria shall be used: <br /> <br />g) A coefficient of 2.6 should be used for typical ..eir calculations. <br /> <br />h} <br /> <br />Design Parameter <br />Bottom width <br />Normal depth <br />Channel depth <br />Manning's n <br />Slo~ slnpp of hdnk~ <br />Slope of river herls <br />bet..eenrlrop<; <br /> <br />7 feet per mile <br /> <br />The br;dqe opening Should be ha~ed on th~ proj~cted area normal to <br />the flow direction. <br /> <br />l04YearEvent <br />750 fef't <br />R.1 feet <br />9 feet <br />0.035 <br />4:1 <br /> <br />, <br />" <br /> <br />No debris blockage of bridges ac~oss the South Platte River is <br />aSSlY'leO,hecau5eofTri-Lakes. <br />