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I I I I I I I I I I I I I I I I I I I I Dry Creek Basin are similar to those used in this study. This information indicates that Douglas Lake is marginally adequate for dischar"e of the lOO-year, flS;~,~,_e"ent. ~~~~jil-m7}tei'~mha~~.t" .. --,--;_, " '._:~','~- -:-:_,-_'----'--.~ - ."'"J"':::~~_.~%';'I.'i>~___ " _'. ,'_, " ,"_' - _ ~ - _,'~ should be. an:a;lyzed for storage""'t:d-:w:frjjhin .5 foot of the ~6:p . ofE!ffiba;~Rfu'$ht be,fbre a Fliilf6if :ttij,tif11;ci~':$tucJ.y is published based on the attenuated discharge. Douglas Reservoir is considered adequate for purposes of completing this hydrologic analysis for Dry Creek at Fort Collins. The drainage basin below Douglas Lake waw analyzed by the same SCS procedure. The drainage area to the downstream study limit is 21.5 square miles and the curve number is 78. The peak discharge at this location is 3480 cfs. The hydrograph is plotted in the Appendix (Fig. 3). The hydrograph from Douglas Lake was lagged by an estimated channel flow time from the Lake to the study limits. The hydro- graph plot in the Appendix (Fig. 3) shows that outflow from the Lake has no effect on the peak discharge at the study site. Since outflow from the Lake has no effect on the peak flow at Fort Collins, analysis of Reservoir No. 15 was not necessary. Outflow from the Lake was also assumed to have no effect for the la-year and 50-year flood events. Frequency discharges were calculated for the la-year, 50-year and laO-year events at the upstream and downstream limits of the flood insurance study. The SOO-year discharge was extrapolated from this data on log-probability paper. This SOO-year discharge does not reflect the overtopping and possible failure of Douglas Lake Dam during the SOO-year event. The discharges recommended for the Fort Collins Flood Insurance Study are listed in Table II. These discharges are contingent upon a detailed engineering analysis of the structural stability of Douglas Lake dam and consideration -4-