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TABLE 13-3-4 Storage Capacity Summary Pond 010 Capacity Elevation Stage (AC.-Ft.l Descrl pt Son 6779.00 0 0 Bottom of Pond Excavation 6785.10 6.10 10.31 Elevation of Principal Spillway d 1008 sediment storage 6788.47 8.q7 19.57 10-Y r, 24-Hr. Peak Stage 6788.50 9.50 19.64 Crest of Emergency Spillway 6790.57 11.57 26.52 25-Y r., 24-Hr. Peak Stage 6791.08 12.08 28.34 100-Yr., 24 -H r. Peak Stage 6795.00 16.00 44.59 Top of Embankment Peabody does not anticipate any other inflow to the pond at [his time. The principal spillway will be nonclogging and will automatically dewater the ponding area to maintain the design capacity for [he runoff volume for a 10-year, 24-hour storm event. Spillways This sediment pond has two separate spillways; a principal and an emergency. Please see Exhibit 13-4 for location of spillways. The principal spillway consists of a 6-inch diameter dewatering orifice cut into a 36-inch CMP riser which drops into the 24-loch CMP barrel. This pipe will keep the pond level at the 6785.1 elevation. Maximum estlmat ed elevation Ipeak stage) above the principal spillway with the passage at the 10-year, 24- hour event will be 6788.47, this leaves 0.03 feet to the emergency spillway (elevation 6788.5). The embankment portion of the emergency spillway consists of a trapezoidal channel as shown on Exhibit 13-4. Assuming the principal spillway was plugged, the trapezoidal channel could safely pass the runoff volume from the 25-year and 100-year, 29-hour storm. The emergency spillway outflow channel consists of an erosion control mat and grass mixture trape zo itlal channel Isee Addendum 13-3-D for specifications). Peak estimated stage elevation with the passage of the 100-year storm is 6791.08. This leaves 3.9 feet of freeboard to the top of embankment. Please refer to Addendums 13-3-A, 13-3-B, and 13-3-C for capacities of both spillways • 13-3-8 Revised 09/08/95