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• TABLE 7-6e-7 <br />Seneca II Mine <br />Design Storage Capacity Summary <br />Sediment Pond 008 <br /> Capacity <br />Elevation Stage (Ac-ft) Description <br />7002.0 0 0 Bottom of Pond <br />7011.0 9 5.04 Elevation of Principal Spillway <br /> and 100% Sediment Storage <br />7013.6 11.6 9.61 10-year, 24-hour Peak Stage <br />7015.0 13 12.46 Elevation of Emergency Spillway <br />7016.6 14.6 16.42 25-year, 24-hour Peak Stage <br />7017.4 15.4 18.39 100-year, 24-hour Peak Stage <br />7020.0 18.0 Top of Embankment Elevation <br />• Peabody does not anticipate any pit pumpage or other flow into the pond at <br />this time. <br />5 illwa <br />Sediment Pond 008 provides for a combination of principal-emergency <br />spillway to safely discharge the runoff from a 25-year, 24-hour storm. <br />The principal spillway inlet will also be used as the nonclogging <br />dewatering device and is located at an elevation higher than the maximum <br />sediment storage volume. The principal spillway inlet is located in a <br />position on the embankment so as to prevent short-circuiting as much as <br />possible. The stage-discharge relationship of the emergency spillway li <br />inlet was calculated using SEDIMOT II, while the stage-discharge <br />relationship of the principal spillway inlet was calculated using the <br />orifice flow equation. <br />Q = C Ao 2~ <br />where: C = 0.6 (constant) <br />• Ao = 0.196 ft.z (6" dia.) <br />g = 32.2 ft/sec.z <br />H = 0 to 8 ft. (above the opening) <br />7-6e-11 <br />