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Appendix B <br />East Yard Pond <br />The information on the preceding pages B-35 through B-39 presents <br />the required capacity of the east yard pond. According to the <br />calculations on page B-38, the 25-year, 24-hour precipitation <br />event produces 10,236.67 cubic feet of run-off volume. The soil <br />loss calculation presented on page B-39 produces a 3 year <br />sediment storage volume of 2000.28 cubic feet. <br />Drawing E8-3404 shows the current size and proposed spillway <br />configuration of the east yard pond. The drawing shows ttie pond <br />will contain the 25-year, 24-hour precipitation event plus the 3 <br />year sediment storage volume. Ttie pond staging chart shows the <br />pond will store the combined water and sediment volume below the <br />level of the primary spillway. <br />The emergency spillway was sized using the computer program Storm <br />ver 6.21. The area and curve number data presented at the bottom <br />of page B-38 was used in the computer program which generated the <br />following results: <br />Watershed Data <br />Curve Number = 74.1 <br />Area = 5.2 acres <br />Hydraulic Length = 1100 feet <br />Elevation Change = 10 feet <br />Concentration Time = 0.32 hours <br />Concentration Time Type = SCS Upland Curves <br />Unit Hydrograph Type = Disturbed <br />Storm Data <br />Total Precipitation = 2.4 inches <br />Storm Type = SCS Type 2,. 25 Yr 24 Hr Storm <br />Peak Discharge = 1.97 cfs <br />Discharge volume = 0.24 acre-feet <br />12" CMP Capacity (no head) = 2.1 cfs <br />The emergency spillway for the east yard pond will be upgraded to <br />a 12" CMP. <br />• B-39a <br />New: 07-06-95 <br />