1991-09-26_REVISION - C1981035 (3)

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r � Table 1. Eastside drainage characteristics. Watershed Parameters for Eastside Drainage Drainage Area = 32.4 acres Length to Divide - 3000 ft Curve Number = 63 Average Slope = 12.8% Lag Time = 15 minutes 100yr-24hr Rainfall Depth = 3.25 in 25yr-24hr Rainfall Depth = 2.90 in 10yr-24hr Rainfall Depth = 2.30 in Table 2. Westside drainage characteristics. Watershed Parameters for Westside Drainage Drainage Area = 24.8 acres Length to Divide - 2500 ft Curve Number = 63 Average Slope = 12.8% Lag Time = 12.6 minutes Mine Yard and Adjoining Areas The portion of the total watershed which will be collected and routed into the sedimentation ponds consists of 11 acres of disturbed yard area and 18.8 acres of undisturbed area. The undisturbed areas were included with the mine yard because of the difficulty in diverting these around the yard. The hydrologic characteristics for this area is shown in table 3. The resulting 10yr-24hr volume needed to size the sedimentation ponds is equal to 1.08 AF for the West Pond and 0.05 AF for the East Pond. The 25yr-24 hour peak flow rate for the West Pond is 8 cfs. This will be used to size the spillway. The peak flow for the East Pond is 1 cfs. Documentation of these results are given in appendix 4. 4. Drainage Structures Pipes and Channel There are 6 sections of pipe in the east and westside drains (labeled as reach 1 through reach 6 on figure 1). The characteristics of each are given in table 4. All pipes were sized using a 4