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I • <br />Watershed Areas Assessment ~ Control Practice <br />Factor <br />Unsurfaced hard- Assessed as Bare Soil Conditions, Compacted 1.20 <br />stands and roads, bulldozer scraped across slope <br />and vegetated <br />areas subject to <br />disturbance by <br />traffic <br />Graveled road- Gravel areas are assessed as providing 100% cov- 0.05 <br />ways and bench er. <br />or pad surfaces <br />5, DITCHES AND CULVERTS <br />With the exception of ditch D-6, a swale, design input parameters include the standard West Elk <br />design of ditches as triangular, with 2 horizontal to 1 vertical side slopes. Swale D-6 is <br />approximated as triangular in cross-section with 20 horizontal to 1 vertical side slopes. <br />Culverts are made of circular corrugated metal pipe (an "n" value of 0.024). The inlets of the <br />pipe are mitered into the road fill slope (a I{e factor of 0.7). Cover over the culverts is a <br />• minimum of 1.2 times the diameter of the culvert or one foot, whichever is larger. The outlets <br />of the culverts are unrestricted. All culverts are placed at a slope of 2 % and are typically 26 <br />feet long. Culverts are evaluated in this demonstration using nomography from the American <br />Iron and Steel Institute (AISI) Handbook of Steel Drainage & Highway Construction Products, <br />using flow values from the SEDCAD+ demonstrations. <br />6. Limitations of the SEDCAD+ Model and Substitutions <br />The minimum flow that SEDCAD+ program will accept for design of erodible ditches is 0.1 <br />cubic foot per second (cfs). Ditches D-SE (Enclosure 17), and D-SW (Enclosure 14), are not <br />anticipated to collect any runoff from a 10-year, 24-hour event; therefore, these ditches are <br />constructed to design flows of 0.1 cfs. <br />SEDCAD+ does not model vegetative (brush) litter as a filter. These structures were equated <br />to grass filters. The maximum slope of a grass filter is 33 %, which is exceeded by actual <br />conditions. However, flows and velocities are so low that the litter would probably remain <br />stable and in place, or rapidly dam up in collections of debris. The ground cover (vegetative <br />debris) of leaves and sticks, grasses, and oak brush root system of the undisturbed natural <br />vegetation slopes was taken as being equivalent to a grass filter of the following description: <br />"n" = 0.01 {approximately the middle of the allowable range, nearly equivalent to a dense stand <br />of fescue); spacing = 0.2" (The distance is taken as representative as the spacing between <br />• (Lone Pine Gulch SAES Demonstration, 12 October 95, Page 9 of 13) <br />