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• <br />Diversion Design and Preliminary EMP Pond Design <br />EMP007 was previously constructed as two ponds performing in series to provide a <br />total volume of about 8.4 acre feet. The proposed MLE will result in more runoff reporting to <br />EMP007 than was planned in Amendment No. 8. That is because EMP008 and EMP009 as <br />approved in the Amendment No. 8 were to be located in terrain that is steep where <br />construction would be may difficult. Under the proposed MLE, these ponds can be made <br />smaller by diverting more water to EMP007. <br />The current size of EMP007 is adequate for a single 10-year/24-hour storm with <br />some extra capacity (6.2 AF fora 10-yr storm vs. existing capacity of 8.4 AF). As part of the <br />MLE, EMP007 will be enlarged by approximately 50% to meet the criteria of 2 times the 10- <br />yearstorm or a total capacity of 12.4 AF. <br />The SEDCAD4 algorithms were used to size the diversion channels. Riprap <br />armoring of the channels was generally assumed to be required for channels steeper than <br />approximately 2 percent, which excludes the bench ditches along the overburden storage <br />area terraces. Those ditches have been designed at a slope of only one percent and may be <br />constructed as grass-lined waterways with no special riprap armoring. The expected velocity <br />will be approximately 3 feet per second ("fps") during the 100-year runoff and mixed grasses <br />will typically sustain velocities of up to 4 fps [Barfield Table 3-4 "Permissible Velocities for <br />Vegetated Channels"., after Ree 1949)]' <br />SEDCAD4 allows the selection of two methods for riprap design in steeper channels. <br />The Simon and Senturk method presented in Chapter 3 of Barfield (1983) may be used for <br />low to moderate sloping channels. That method tends to be overly conservative for steeper <br />channels where the PADER method is more appropriate. The Simon method was generally <br />used to model channels for the lower magnitude 10-year/24-hour? storm event. The riprap <br />size was verified by the PADER method to be appropriate for the higher magnitude, but less <br />frequently occurring, 100-year/24-hour? storm. The riprap size that would satisfy both criteria <br />is shown on the table of Drawing CCVA9-SA-1. <br />Barfield, B.J., R.C. Warner, and C.T. Haan, `Applied Hydrology and Sedimentology for <br />Disturbed Areas'; U. of Kentucky, 1983. <br />Client:CC8~V Gold Mining Co. 4/11/08 <br />Title: Storm Water Management, MLE Page 12 <br />