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r~ L Due to similarity in channel slopes and unit discharges, a single riprap gradation can be utilized to stabilize the channels in every area considered. Gradation criteria for the riprap are as follows: Percent Finer Rock Diameter By Weight (inches) 100 27 50 18 20 9 10 6 • Tables 2 through 8 summarize the important hyoraulic, geometric and riprap criteria applicable to the channels considered. Hydraulic information is also found on Sheets 3 through 7. Granular Bedding Due to the relatively steep slopes and fine-grained nature of the underlying material, a granular filter layer is required beneath the riprap. Generalized criteria for bedding specified in the Urban Storm Drainage Criteria Manual specify either a two layer filter consisting of Type I and Type II bedding meeting specifications given in Table 9, or alternatively a one-foot thick layer of Type II bedding. Estimated Quantities Table 10 provides estimates of the quantities of riprap and granular bedding required to construct the proposed channel improvements. SEDIMENT YIELD CALCULATIONS Soil loss in tons/acre/year and sediment yield in tons/year were estimated for the major drainage channels of the Eckman Park Mine using the Universal Soil Loss Equation (LISLE). Estimates were made for approved and existing drainage ways (Table 11). Soil loss is converted to sediment yield by multiplying by drainage area and by a sediment delivery ratio. The latter is a percentage of the soil eroded which is actually removed from the watershed rather than stored by depositional processes. Sediment delivery ratio was determined using a relationship between drainage area and sediment delivery ratio presented by Wischmeier and Smith (1978). The LISLE predicts soil loss (here expressed in tons/acre/year) on the basis of five factors as follows: 1) rainfall and runoff factor (R); 2) soil erodibility factor (K); 3) topographic factor (LS, incorporating slope-length (L) and slope gradient (S)); 4) cover and