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I • <br /> <br /> <br />Culvert C-4 receives the discharge from Ditch D-10. Ditch D-10 receives the discharge from <br />D-9, and collects runoffs from Watershed 19 (the natural slope above the ditch) and Watershed <br />20 (a road between the Staging Area and Culvert C-4). Ditch D-9 collects runoff from <br />Watershed 17 (the natural slope above the ditch) and Watershed 18 (the eastern portion of the <br />Staging Area}. <br />Runoff from Watershed 21, the fill slope of the Staging Area, flows directly down the slope, <br />through filter fencing, to vegetative debris (filter) along the base of the slope. <br />Best management practices of ditch feather distribution and silt fences or straw bales for energy <br />dissipation, and silt fences to arrest erosion, have been added to the facility to enhance the <br />distribution of sheet runoff into the vegetative debris filters at the toe-of-slopes of the Staging <br />Area fill and the Topsoil Storage Pile. Neither filter fences or straw bales are evaluated as <br />contributing factors in the SAE effluent analysis. <br />Fill slopes are seeded and mulched. Cut slopes are protected with Soil Guard (trade name of <br />sprayed protective duff). In the analyses for runoff quality, fill slopes are considered as bare soil <br />(a "worst case" scenario). <br />The berms located at the front edge of the Fan Bench and the Staging Area are not features of <br />the drainage system. The berms are seeded and mulched. <br />2. SEDCAD+ INPUT PARAMETERS COMMON TO ALL <br />ANALYSES <br />2.1 Storm Type <br />The Stone Type was selected as SCS Type II. The SEDCAD+ model (hydrograph convolution <br />interval) time increment was selected as 0.1 hour. <br />2.2 Soil Type <br />The sites are located within Soil Mapping Unit Number 31 (Permit). The soil type is <br />representative of the Holderness, Morop, Absarokee, and Work Series, among other similar soils <br />(Permit). SEDCAD+ soil input parameters include (Soils of Colorado, Loss Factors and <br />Erodibility Hydrologic Groupings, 1983, Soil Conservation Service) an overall classification as <br />loam (SEDCAD+ classification of ordinary firm loam), K (a measure of susceptibility of soil <br />particles to detachment and transport by rainfall and runoff) soil erodibility = 0.32, and a <br />hydrologic group of C. <br />(Lone Pine Gulch SAES Demonstration, 12 October 95, Page 4 of l3) <br />