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sediment from the SEDCAD model needs to be increased by a factor of 2.24 to determine <br />the annual amount. <br />Controlling Runoff using Dozer Basins <br />Controlling sediment from lands with recent reclamation is of primary concern to the mine <br />in order to minimize repair and maintenance costs associated with the check dams and <br />other downstream structures as a result of deposition. <br />While not required by any regulatory requirement, the recommended method of <br />controlling runoff from recently reclaimed lands is to construct a sufficient number of dozer <br />basins to completely contain all runoff from all lands with a curve number of 83. This is <br />based on an assumption that the worst case condition is 50% of the area recently <br />"topsoiled and seeded" and 50% with one year reclamation. Under this design basis, the <br />amount of sediment the storm produces is not relevant as the entire amount of sediment <br />is retained in the dozer basin and does not report downstream. When combined with the <br />previously described methods for the number of check dams, and by not considering the <br />small storage provided by the check dams relative to dozer basins, this guideline provides <br />for some level of "over -design" and maintenance minimization. <br />Using the hydrology and sedimentology data provided in Appendix H and as presented <br />in Table 2, it is possible to summarize the results graphically. Figure 9 provides a graph <br />of Total Runoff Volume versus Drainage Area. Notice that this graph is independent of <br />the watershed slope. This Figure provides the basis for determining the number of Dozer <br />Basins recommended for newly reclaimed lands. As noted by the recommended design <br />basis stated above, Curve Number 83 results in 0.0214 acre-feet of storage needed for <br />every acre of watershed. <br />Following is an example calculation of how this would be used with the factors shown on <br />Figure 9. For an upstream watershed with mixed amounts of reclamation consisting of <br />30 acres of lands with curve number 83, 40 acres of lands with curve number 80, and 25 <br />acres of lands with a curve number of 78, the recommended storage capacity in acre-feet <br />is: <br />30(0.0214) + 40(0.0158) + 25(0.0127) = 1.59 acre-feet storage required. <br />Typically, the Trapper Mine uses dozer basins to contain sediment in areas near recently <br />reclaimed lands. These structures are always less than 2.0 acre feet in capacity and are <br />excavated (subgrade). Figure 8 shows one method of construction, where a large <br />excavator simply digs out in an arc pattern as far as practical. Interior basin sideslopes <br />are built at 3H:1 V or less. Excavated depths are generally 7 to 10 feet. The storage <br />capacity can be expanded from the amount shown in this example by relocating the <br />excavator and creating a more rectangular shape. The location and capacity of dozer <br />basins is largely dependent of the surrounding topography and the flatter areas are much <br />more conducive to achieving adequate capacity. <br />10 <br />