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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />7. BIG JOHNSON RESERVOIR/CREWSGULCH DRAINAGE BASIN <br /> <br />7.1. Watershed Description <br /> <br />The Big Johnson Reservoir/Crews Gulch drainage basin is located in central EI Paso County, <br />north of the City of Fountain, and east of the unincorporated area 01 WJdefield (FIgure 7.1). The basin <br />is bounded by Jimmy Camp Creek basin on the east, Windmill Gulch on the northwest. and the UtUe <br />Johnson/Security Creek basin on the southwest. The total basin area is 8.47 square mnes. <br /> <br />Streamflow in the basin is significantly affected by irrigation faciities. These include two <br />reservoirs: Big Johnson Reservoir located in the portion of the basin and McRae Reservoir which is <br />s~uated in the central portion of the basin, Big Johnson Reservoir has a surface area of approximately <br />300 acres and a storage capacity of approximately 3,950 acre-feet, McRae Reservoir is much smaller <br />w~h a surface area of approximately 14 acres and a significanUy reduce stOlllge capacity due to <br />sedimentation, <br /> <br />The basin contains both urbanized and undeveloped lands. The urbanized area is located <br />primarily downstream of Fountain Boulevard. The remainder of the watershed consists of open space <br />and upland grassland, Soils in the watershed are primanly of hydrologic Type "B" as categorized by <br />the SCS, Type "A" soils are found in the majority of the basin upstream 01 Big Johnson Reservoir and <br />a relatively minor amount of Types "C" and "0" soils are found din the central portion of the basin, <br /> <br />7.2. Previous Studies <br /> <br />Two previous studies were available for review. These were the FrS - EI Paso County, <br />Unincorporated Areas (Ref. 6.1) and the Big Johnson Reservoir/Crews Gulch Drainage Basin Planning <br />Study (Ref, 7,1), The FIS used synthetic un~ hydrographs to develop peak discharges, The Big <br />Johnson Reservoir/Crews Gulch Drainage Basin Planning Study used methods previously specified In <br />Colorado Springs drainage criteria to compute peak discharges. However, this study estimated <br />discharges associated w~h the 1 DO-year, 2-hour stonn duration with AMC III, Current specifications <br />require use of the 24-hour duration stonn w~h AMC II cond~ions, In addition, contribution from Security <br />Creek was not accounted for using consistent stonn methods, <br /> <br />Peak discharges at the confluence w~h Fountain Creek are presented In Table 7.1 for the two <br />studies, <br /> <br />7,1 Resource Consultants & Engineers, lnc, <br />