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• distinct hydrologic region of the watershed, using the values in Table <br />2. An overall curve number for the subwatershed was derived by <br />calculating a subwatershed weighted average based on the relative <br />acreage of each distinct hydrologic region. The runoff was then routed <br />into the sediment structure (see Table I). <br />Precipitation and Storm Type <br />Precipitation depths for the 10-year, and 25-year storms were developed <br />using procedures and data published in the Soil Conservation Service <br />publication "Procedures for Determining Peak Flows in Colorado". A <br />standard SCS Type II storm was utilized for each analysis. <br />Unit Hydrograph and Surface Condition <br />The SEDIMOT II computer program provides three unit hydrograph shapes to <br />choose from in determining the runoff characteristics of a subwatershed. <br />In general, the agricultural hydrograph (No. 2) was used for <br />agricultural and undisturbed areas. The disturbed hydrograph (No. I) <br />• was used for disturbed and reclaimed areas. <br />Travel Time <br />The travel times from subwatershed to structure were determined <br />utilizing the Manning Equation. In using this method, the flow velocity <br />is determined by flow rate and channel characteristics. The travel time <br />will be the result of dividing the channel length by the velocity. <br />Time of Concentration <br />The time of concentration for each subwatershed was determined using the <br />SCS Upland Method. In using this method, the longest flow path in each <br />subwatershed is divided into segments of uniform flow characteristics. <br />Within each segment, the travel time is estimated by dividing the flow <br />length by the velocity. The time of concentration is the sum of these <br />travel times. <br /> <br />4 <br />