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A conservation practice of "Permanent Pasture, Rangeland, Idle Land, and Grazed Woodland" was selected as <br />representative of the natural site. Vegetative cover was evaluated as Appreciable Brush, 2 meters tall, 50 % Canopy <br />Cover, 60% Ground Cover. The CP value selected was 0.038. <br />For bare, unprotected soil, a CP of 0.80 (loose to 12 inches, rough) was used. <br />5. INTERCEPTOR DITCH AND POINT DISCHARGES <br />Design input parameters include the standard West Elk triangular ditch design of 2 (horizontal) to 1 (vertical) side <br />slopes. <br />During construction, the erodible fraction of the soil matrix is expected to be rapidly removed, leaving a protective <br />armor (ditch lining) of cobble sized materials in the circumvential ditches. Thus the circumvential ditch material <br />is described as "graded silts - cobbles colloidal ". The maximum allowable velocity of such a protective ditch lining <br />is 5.50 feet per second (fps). <br />6. LIMITATIONS OF THE SEDCAD+ MODEL AND <br />SUBSTITUTIONS <br />SEDCAD+ does not model silt fences or straw bales. No contribution to sediment control or mitigation of affects <br />on water quality was made in this analysis. <br />SEDCAD+ does not model forest (brush) litter as a filter. The litter was equated to a grass filter. Equivalent grass <br />filter input parameters used were: <br />• 1} a slope of 20 %. <br />2) a Mannings "n" value of 0.01 (a very dense grass). <br />3) a spacing of 0.2 inches (between grass stems). <br />4) a height of 2 inches. <br />5) a filter width of 390 feet (the lower perimeter of the pile). <br />6) an infiltration rate of 0.1. <br />7) a stiffness factor of 20. <br />8) a length of 30 feet. <br />7. SEDCAD+ ANALYSIS INFORMATION <br />The Small Area Exemption SEDCAD+ demonstration (Enclosure 3) indicates that the Peak Settleable Concentration <br />of discharges (10 -year, 24 -hour precipitation event) from the vegetative debris filter as 0.00 mill. The 100 -year, <br />24 -hour precipitation event demonstration (Enclosure 4) indicates that the Peak Discharge (flow) in Ditch DWP-W <br />is projected as 0.26 cubic feet per second (cfs), and 0.27 cfs in Ditch D"-E. <br />• (West Elk Lone Pine Gulch Development Waste Pile SAE, 12 October 1995, Page 6 of 7) <br />