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-zF- <br />t <br />2. Criteria for Sizing Settling Ponds and Drainage Plan <br />According to the Surface Mining Control and Reclamation Act (PL95-87), a <br />sediment storage capacity of 0.2 acre-foot per acre disturbed must be provided <br />in addition to sufficient capacity to control runoff from a 10-year, 24-hour <br />storm. However, the 0.2-acre-foot requirement may be reduced, depending on <br />the amount of erosion control upstream from the settlinq ponds. "Credits" are <br />given for such controls as revegetation of slopes and surface drainage control <br />systems. <br />Plate I (100-scale map) shows the drainage plan. The plan involves <br /> <br />realignment of Curtis Creek and diversion of storm runoff from side drainages. <br />This runoff would be collected above the mine area and conveyed underground <br />through 24 and 30-inch currugated metal pipes. <br />The new reach of Curtis Creek will flow through a structural plate pipe <br />arch with sufficient inlet capacity to pass a 25-year, 1-hour storm event <br />1/ <br />(Figure 10) Beyond this capacity, the channel bank and flood-plain configuration <br />in this reach will be adequate to pass the peak runoff from at least a 100-year <br />event as required by OSt9 regulations. <br />a. Predicted Erosion from Kline Site. Because "credits" are allowed for <br />drainage and on-site erosion control, the analysis presented below was made to <br />determine the amount of dead storage capacity that should reasonably be designed <br />into the system. The modified Universal Soil Loss Equation (LISLE) recently <br />developed by Utah State University (1916) was used to estimate potential erosion <br />and to also numerically show to what extent the proposed reclamation program <br />will reduce erosion upstream from the proposed settling ponds. The procedure is <br /> <br />reviewed in some detail in Appendix IV. However, the reader is also encouraged to <br />consult the Utah State (1976) reference for a comprehensive treatment of the <br />suhject. <br />~~Q = 750 c.f.s. CN 75 (Figure 10). <br />