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. The precipitation values were obtained from the Precipitation Frequency Atlas of <br />the Western United States, Volume 3, Colorado, (NOAA, 1973). <br />Hydrograph Response Shape. A unit hydrograph was chosen for each drainage <br />area or sub-area model to predict the runoff response. The hydrograph <br />responses available in the SEDCAD+ model are slow, medium, and fast. A slow <br />response corresponds to a forested area, or an area with a number of <br />obstructions, whereas a fast response corresponds to an unvegetated or poorly <br />protected area. For each of the areas modeled, the appropriate runoff hydrograph <br />was chosen. <br />The internal convolution increment is 0.05 hours and values are saved at the user <br />specified interval of 0.1 hours or greater. (A convolution increment of 0.1 was <br />specified for all pit areas). It should be noted that a time of concentration less <br />than 0.125 hours bypasses the unit hydrograph technique and instantaneous <br />• runoff is assumed. As explained in the SEDCAD+ User's Manual, page 113, the <br />time of concentration restriction of 0.125 hours is somewhat mandated due to a <br />combination of array size restrictions, minimum internal convolution interval, and <br />the user-specfed time increment for saving convoluted values. <br />Drainage Basin Area. The drainage areas were determined by digitizing directly <br />from a 1°=400' scale map. <br />Time of Concentration, Tc. Time of concentration was calculated by using the <br />SCS Upland Method as presented in Barfield, et al., (1981) page 100. All hydraulic <br />lengths, drainage heights, and slopes were measured directly from 1"=400' scale <br />maps. <br />Curve Number CN. The runoff curve number (CN) is a factor relating the amount <br />of rainfall to the amount of runoff for a given area. It is dependent upon the <br />. infiltration characteristics of soil types and the type and amount of vegetation. <br />3 <br />