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Mr. Forrest Luke • February 2, 1995 Page Two Inputs to the hydrology component of the SEDCAD+ Computer Model include: • Precipitation Distribution • Storm Duration • Return Period/Precipitation • Hydrograph Response Shape • Drainage Basin Area • Time of Concentration • Muskingum Routing Parameters • Curve Number Input values aze shown on the SEDCAD+ printouts and explained in the following sections. Precipitation Distribution A precipitation distribution is input to model the run-0ff hydrograph. SEDCAD+ allows the user to choose between the SCS Type I and Type II Storms. The SCS Type II Storm was input as a standazd representation of Colorado storms. • Storm Duration A storm duration of 24-hours was used for this study. Return Period/Precipitation A precipitation amount is required for the appropriate return period. For the Trapper Mine, the following precipitation amount, supplied by Trapper Mining Company, was used: 25-year, 24-hour storm event: ].8 inches Hvdro¢raph Response Shane A unit hydrograph is chosen for each drainage area or sub-area modeled to predict the run-0ff response. The hydrograph responses available in the SEDCAD+ model are slow, medium, and fast. A slow response corresponds to a forested area or an area with a number of obstructions. A fast response corresponds to an unvegetated or poorly protected area. Fast and medium hydrograph responses were chosen for disturbed and undisturbed areas, respectively. The internal convolution increment is 0.05 hours, and values aze saved at the user specified interval of 0.1 hours or greater. A convolution increment of 0.1 was specified for the Trapper Mine. It should be noted that a time of concentration less than 0.125 hours bypasses the unit hydrograph technique and instantaneous run-0ff is assumed. As explained in the SEDCAD+ User's Manual (Schwab and Warner, 1987, pg. l 13), the time of concentration restriction of 0. l25 • hours is somewhat mandated due to a combination of array size restrictions, minimum internal convolution interval, and the user specified time increment for saving convoluted values.