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SEDCAD model allows for an estimate of the annual sediment collected in the pond. The <br /> methodology is described on page 64 of the SEDCAD User's Manual, and requires an Annual R <br /> factor (rainfall-erosivity factor). The value of R at 27 can be interpolated from Figure 5.3 <br /> presented in Barfield, Warner and Haan (1981). In addition the total tonnage of sediment from <br /> the modeled storm, in this case 10 year, 24 hour storm, is required. This is obtained from the <br /> SEDCAD output by subtracting from tons flowing into the pond (63.7 tons) the sediment <br /> tonnage into the null below the pond (21.2 tons). <br /> The net 42.5 tons from a single 10 year, 24 hour storm is converted to annual tons via the method <br /> described in the SEDCAD User's Manual to 60.9 tons. This weight is then converted to volume, <br /> using a density of 78 lb/cu ft, to arrive at the projected annual volume collected in the pond of <br /> 0.036 ac-ft. According to the stage-storage curve, there are 2.40 ac ft of available storage <br /> between the pond floor (elevation 5549) and the invert of the twin 6-inch valves on the riser. <br /> Thus, over a period of 10 years approximately 0.36 ac-ft of sediment would be accumulated in <br /> the pond bottom with the watershed in its current revegetated condition. This is small enough to <br /> not significantly affect the trap efficiency of this pond. <br /> The SEDCAD printout shows the 10 year, 24 hour storm flows in Ditch C9 to be 4.65 cfs in the <br /> 10 year storm, and flowing at a velocity of 1.4 fps, well below the allowable velocity of 7 fps for <br /> the grass lined channels at these conditions. <br /> Following establishment of the postmining topography to final grade, an inlet ditch into the pond <br /> will be excavated as shown on Map 2.05.3(3)-32. Details of this inlet channel, along with <br /> dimensions and erosion protection details and other information is also provided for this feature. <br /> REFERENCES <br /> Barfield, Warner, & Haan (1981). "Applied Hydrology and Sedimentology for Disturbed Areas". <br /> Oklahoma Technical Press, Stillwater, OK. <br /> Renard, K.G., G.R. Foster, G.A. Weesies, D.K. McCool, and D.C. Yoder (1996). "Predicting <br /> Soil Erosion by Water: A Guide to Conservation Planning with the Revised Universal Soil <br /> Loss Equation (RUSLE)". Agricultural Handbook No. 703. U.S. Department of <br /> Agriculture. Washington, DC. <br /> Schwab and Warner(1998). "SEDCAD4 Users Manual". Civil Software Design. Lexington, KY. <br /> Soil Conservation Service (1986). "Urban Hydrology for Small Watersheds (TR-SS)". Soil <br /> Conservation Service. Washington, DC. <br /> Striffler and Rhodes (1981). "Hydrologic and Erosional Characteristics of Regraded Surface <br /> Coal Mined Lands in Colorado", Dept. of Earth Resources, Colorado State University, Ft. <br /> Collins, CO. <br /> USDA (January 2009), National Resources Conservation Service, National Engineering <br /> Attachment 2.05.3(3)-32 Revision Date: July 2020 <br /> Page 4 Revision No.: TR-99 <br />