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4.4 Control Practice Factor <br />The SEDCAD+ Model considers the sediment loss from an area with a given cover and conservation practice <br />to that of a field in continuous fallow by introduction of a Control Practice (CF) Factor. The CP is a function <br />of Canopy Cover and Percent Ground Cover. A conservation practice of "Permanent Pasture, Rangeland, Idle <br />Land, and Grazed Woodland" was selected as representative of the natural site. Vegetative cover was assumed <br />to be Appreciable Brush, 2 meters tall, 50% Canopy Cover, 60% Ground Cover. The CPs used were <br />(reference the SEDCAD± guide): <br />For the natural site: 0.035. <br />For the cut slope: 0.90 (Bare Soil Conditions, rough, irregular, tracked all directions). <br />For the pad: 0.005 (reference the SEDCAD+ help screens, 100% gravel cover). <br />For the tank: 0. <br />5. INTERCEPTOR DITCH AND POINT DISCHARGES <br />The interceptor ditch is required to handle 0.01 cubic foot per second (cfs). Runoff from the watershed above <br />the tank and the interceptor ditch is 0.02 cfs (see Attachment 2). However, this runoff is split equally towards <br />both sides of the tank (each leg being approximately 56 feet long). It was designed to handle 0.1 cfs (the <br />minimum the SEDCAD+ program will accept. <br />Design input parameters included the standard West Elk design of ditches as triangular, with 2.5 horizontal <br />to 1 vertical side slopes. The channel bottom matrix is described as a noncolloidal silt loam with a Manning's <br />"n" of 0.02. The maximum allowable velocity of water (3 cfs) over the soil was from SEDCAD+. The 0.3 foot <br />of freeboard is required by the Division of Minerals and Geology. <br />The outfall of the interceptor ditch would be tapered (feathered) to flat over a distance of approximately 5 <br />feet to distribute runoff (and to dissipate energy) over the grassland discharge area. Point discharges from the <br />upslope side of the pad and cutslope would be similarly spread out over 8 feet by the use of hay bales. One <br />of these point discharges would be located on the downslope side of the access road. Due to the low flows <br />anticipated, a water bar is recommended to convey the water across the access road in-lieu-of a culvert. <br />6 SEDCAD+ ANALYSIS INFORMATION <br />SEDCAD+ run results are summarized in the following tables: <br />Description I Peak Discharge j Sediment (tons) i Peak Sediment Peak Settleable <br />(cfs) ! Concentration Concentration <br />(mgM i (ml/1) <br />Runoff from the 0.02 i <br />watershed above <br />the interceptor <br />ditch