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I I I I I I I I I I I I I I I I I I I Table 7.1, Summary of Big Johnson Reservoir/Crews Gulch Hydrology from Previous Reports. Repoit Drall13gllArll3 (sq\.i?r~ri\il~s) __ __ __ - - ___ - __,__ _________"',........___"'_ - d_ _".." -'",-',. .".......... ----."' - ..............."..".--........... ,-".""..".."".",...".."."......,-.,-.,-.,---.. --.. --,,--.......-....-..-----.-.--..-....--..-.-..----.--....-.-----'"'-,..'-' ........,.............~~'lllIgBi~J~~....'..........,.........'.... " , 5OO-Y_ri FIS (5-4) BJCGBPS. 5,38 2,37 1,600 1980 3,400 5,000 4,880 14,500 . Big Johnson Reservoir basin was assumed to be hydrologically unconnected to the basins lying below Big Johnson Reservoir, Big Johnson drainage area is 3,07 sq, mi. 7.3. Hydrologic Analysis The Big Johnson Reservoir/Crews Gulch drainage was analyzed using the TR.2Q model (Ref, 1,2). This model was obtained from the Big Johnson Reservoir/Crews Gulch Drainage Basin Planning Study (BJCGDBPS) and modified to estimate runoff from both the l00-year, 24-hour and 2-hour rainfall events, The outflow hydrograph from the combined Security Creek and Windmill Gulch overflow was added to the Crews Gulch hydrograph within the TR,20 model, Table 7.2 summarizes the peak discharges for the key locations shown in Figure 7,1, Because this is a limited detail study, peak discharges are only shown for the 100-year flood, Peak discharges associated with the 24-hour storm were recommended by EI Paso County for use in floodplain analyses in order to remain consistent with drainage basin planning studies, In addition, the 2-hour storm generates higher peak discharges; therefore, it will produce conservative results, The increased inflows from the BJCGDBPS are due to the increases in Security Creek flows resulting from inflow to the basin from Windmill Gulch overflows at Canal #4 and Grand Avenue and from additional inflow west of Grinnell, 7,3 Resource Consultants & Engineers, Inc.