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The locations of the culverts are shown on Exhibit 7-19, Postmining P)iainage Control. Appendix C <br />contains the hydraulic calculations for permanent culverts, while Appendix 12-2 contains all <br />original culvert designs. <br />2.0 METHODOLOGIES AND ASSUMPTIONS <br />2.1 SEDCAD+ Hydrologic Computer Model <br />Calculations for the postmine channels and culverts were performed using the SEDCAD+ <br />computer model (Civil Software Design, 1986). <br />SEDCAD+ is a hydrologic, hydraulic and sediment calculation model designed for use on computer <br />systems. The SEDCAD+ hydrologic model calculated run-off volume, and peak flow via a <br />numerical modeling technique based on user inputs of the design storm event (i.e., precipitation <br />frequency data, selection of rainfall distribution, and convolution increment). Hydrographs are <br />developed on a subwatershed basis with the input of azea, time of concentration, SCS curve number <br />and the selection of a hydrograph shape. Routing of hydrographs is accomplished by the <br />Muskingum 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 />• Watershed area <br />• Time of concentration <br />• Muskingum routing parameters <br />• Curve number <br />Input values used in this model are shown in the SEDCAD+ demonstrations presented in <br />Appendix A and aze explained in the 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 Type I and Type II storms. The SCS Tyl>e II storm was used for the <br />Seneca II Mine area. <br />Storm Duration <br /> <br />A storm duration of 24 hours is used to model the watershed for the Seneca II Mine area. <br />TR-41 7-12-2 Revised 03/07 <br />