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<br />Table 1 <br />Safety-Related Maintenance Cherry Creek Lake <br /> <br />Item <br /> <br />Cost <br /> <br />Year <br /> <br />Construct pilot channel in outlet channel <br />to improve drainage and expose relief <br />well outfall <br /> <br />$ 21,000 <br /> <br />1983 <br /> <br />Remove consolidated sediment from intake <br />structure by dredging <br /> <br />182,000 <br /> <br />1984 <br /> <br />Installation of emergency gates in intakE! <br />structure <br /> <br />329,700 <br /> <br />1984 <br /> <br />TreE! removal from spillway <br /> <br />84,300 <br /> <br />1983 <br /> <br />Install low flow gates <br /> <br />69,600 <br /> <br />1988 <br /> <br />RUNOFF CHARACTERISTICS <br /> <br />Major floods in the Cherry Creek basin are usually caused by shClrt periods <br /> <br />of intense rainfall occurring over a small portion of the basin. NinE!ty percent <br /> <br /> <br />of the floods on Cherry Creek have occurred during the period of May to <br /> <br /> <br />September. The steep slopes in the basin caUSE! rapid concentration of runoff and <br /> <br />peak discharges are experienced at the Cherry Creek Dam within 3 to 4 hours after <br /> <br /> <br />l:he beginning of runoff producing rainfall. <br /> <br />UNIT HYDROGRAPH <br /> <br />The unit hydrograph for the area upstream of Cherry Creek Dam WElS based on <br /> <br />l:he unit hydro graph developed from the flClod of June 1965, <br /> <br />In order to <br /> <br />acconunodate alternatives involving Castlewood .Darn, a supplemental reservoir <br /> <br /> <br />upstream from Cherry Creek Dam, the unit hyclrograph at ChE!rry Creek Dam was <br /> <br /> <br />subdi vided by developing uni t hydro graphs for the 17 5 - square -mile area upstream <br /> <br />of the Castlewood Dam site and the 210-square"mile are~i between the Castlewood <br /> <br /> <br />Dam site and Cherry Creek Dam. Snyder's constants used in the individual unit <br /> <br /> <br />hydrographs were Ct - 0.51 and 640 Cp '. 537. The routing param,eters were <br /> <br /> <br />determined by trial and error using a lag-average procedure. The goal was to <br /> <br />IS <br />