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<br /> <br />CONCLUSION <br /> <br />Flood peaks developed during 1979 for North Clear Creek, Gregory Gulch, and Chase <br />Gulch for the City of Black Hawk were reconstituted using the SCS TR20 computer <br />model. Similar to the 1979 analysis, the TR20 model uses a SCS "Type IA" distribution <br />for North Clear Creek and a SCS "Type II" precipitation distribution for Gregory and <br />Chase Gulch. Assuming Hydrologic Soil Group "B" soils, an ARC (AMC) of II, and <br />1979 land use, an average Curve Number of 79 was calculated for the study area. The <br />curve number was used to calibrate the TR20 model to 1979 flood peak calculations, and <br />the calibration resulted in a slight lowering of the average Curve Number in the study <br />area to 75.5, The Curve Number of 75.5 is within the range of curve numbers used for <br />other studies in the catchment which, ignoring the unrealistically low curve number of 55 <br />used by Futura, ranged from 69 to 85. <br /> <br />The construction of reservoirs within Chase and Gregory Gulch watersheds reduce the <br />magnitude of flood peaks downstream of the reservoirs. Chase Gulch Reservoir reduces <br />the magnitude of historic I DO-year flood peaks by approximately 50 per cent at the outlet <br />of Chase Gulch. Dorothy Lee Reservoir has only a minor effect on the magnitude of <br />100-year flood peaks at the outlet of Gregory Gulch. At the downstream limit of the <br />study area along North Clear Creek, 100-year flood peaks are reduced by approximately <br />200 cfs. <br /> <br /> <br />-14- <br /> <br /> <br />