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hf~ l998 Sw•m pMw+RutMi~ Dnsiwp Conn! • 2 <br />METHODOLOGIES AND ASSUMPTIONS • <br />SEDCAD+ HYDROLOGIC COMPUTER MODEL <br />Calculations For all the channels and arlver6 were perfoaned utilizing the SEDCAD+ computec <br />model developed by Civil Software Design. <br />SEDCAD+ is a hydrologic, hydraulic, and sediment calculation model designed foc ease on computer <br />systems. The SEDC.9D+ hydrologic model calculates run-off volume, and peak Qow via a numerical <br />modeling technique based on user inputs of a design stoan event, (.e., precipiratiott frequenry data, <br />selection of rainfall distribution, and convolution increment). Hydcographs are developed on a <br />subwatershed basis with the input of azea, rime of concentration, SCS curve number, and the <br />selection of a hydrograph shape. Routing of hydrographs is accomplished by the Muskingum <br />Method. <br />Inputs to the hydrology component of the SEDCAD+ computer model include: <br />• Precipintion Distribution <br />• Storm Duration <br />• Retum Period/Pceupitauon <br />• Hydrograph Response Shape <br />• Drainage Basin Area <br />• Time oEConcentration <br />• Muskingum Routing Parameters <br />• Curve Number <br />Input values used in this model, are shown on the SEDCAD+ printouts and aze explained in the <br />following text. <br />Precipira~oo Dictribudoo <br />• <br />A precipicttion distribution is input ro model the runoff hydrograph. SEDG~D+ allows the user to <br />choose between the SCS Type I and Type II Sromu. The 5CS Type R Storm was used Eoc the Seneca II • <br />Mine area. <br />7-12-2 Revised 05/08/98 <br />