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-11- • For Pond A, flow will be conveyed down the haul road embankment from the 60-inch RCP emergency spillway. It will be conveyed down the emban'~cment in a riprap lined channel which is shown in cross-section on LRCWE Figure 4, Sedimentation Pond A, Emergency Spillway Channel. An adequate energy dis- sipator should be installed at the toe of the slope. REQUIRED SEDIMENTATION VOLUMES 30CFR816.46 (b) provides two methods for computing required sedimentation volumes. The first is the product of 0.1 acre-feet per acre and the total number of disturbed acres during the mining and reclamation activities. For the 10 pond sites, this method was used to determine an approximation of the sedimentation volume. For those sites which required greater than 20 feet or greater than 20 acre-feet to contain the sum of the required sedimentation volume and the 10-year inflow flood, the required sedimentation volume was computed using the alternate technique. The alternate technique utilizes the • Universal Soil Loss Equation (LISLE), gully erosion rates, and sediment del- ivery ratios. The total of eroded material which would accumulate from three years of average erosion was converted to a sediment volume using appropriate sediment density data. Tie form of the LISLE used in this analysis is A = R(K) (LS) (VM), which is the more applicable form of the equation for surface coal mining and reclamation activities. It is described in an art- icle titled "Highway Erosion Control Systems- an Evaluation Based on the Uni- versal Soil Loss Equation" which was published in Soil Erosion: Prediction and Control, published and copywrited in 1976 by the Soil Conservation Society of America. The VM factor accounts for the effects of all erosion control measures which may be applied to any given site, including planting vegetation, physical changes, and application of chemicals. The factors R, K, and LS are defined in Technical Release Number 51, published by the Soil Conservation Service in 1977. Erosion control measures which will be undertaken as part of the mining and reclamation plans are more fully described in Section 780.21 of the application. The most critical year from the point of view of generation of sediment was determined for each site. For this analysis, a VM • factor ranging from 1.0 for all disturbed areas with nv ground cover, to a value of 0.05 for all areas permanently seeded after 12 months was used. The Leonard Rice Consulting Water Engineers. Inc.