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METHODOLOGIES AND ASSUMPTIONS • <br />SEDCAD+ HYDROLOGIC COMUPTER MODEL <br />Calculations for all the channels and culverts were performed utilizing the SEDCAD+ computer <br />model developed by Civi] Software Design. <br />SEDCAD+ is a hydrologic, hydraulic, and sediment ca]culation model designed for use on computer <br />systems. The SEDCAD+ hydrologic model ca]culates run-off volume, and peak flow via a numerical <br />modeling technique based on user inputs of a design storm event, (i.e., precipitation frequency data, <br />selection of rainfall disuibution, and convolution increment). Hydrographs are developed on a <br />subwatershed basis with the input of area, time of concentration, SCS curve number, and the <br />selection of a hydrograph shape. Routing of h}'drographs is accomplished by the Muskingum <br />Method. <br />Inputs to the hydrology component of the SEDCAD+ computer model include: <br />• Precipitation Distribution <br />• Storm Duration <br />• Return Period/Precipitation <br />• Hydrograph Response Shape <br />• Drainage Basin Area <br />• Time of Concentration <br />• Muskingum Routing Parameters <br />• Curve Number <br />Input values used in this model are shown on the SEDCAD+ printouts and are explained in the <br />following text. <br />Precipitation Distribution <br />A precipitation distribution is input to model the run-off hydrograph. SEDCAD+ allows the user to <br />choose between the SCS T}pe I and Type II Storms. The SCS Type II Storm was used for the <br />Seneca II Mine area. <br />• <br />• <br />TR-36 7-12-2 Revised 09/98 <br />