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• OUTLET YORKS <br />Primary Outlet Morks <br />Riser type outlets were designed for the ponds to achieve the <br />theoretical detention time required by 30 CFR 816.46(c). A Type 3 riser <br />constructed of corrugated metal pipe was designed for each of the ponds <br />with a 24-inch vertical riser pipe and and 18-inch conduit. The Type 3 <br />riser has one (1) to three (3) orifices set at the required <br />sedimentation level varying in size for each pond. The top of the riser <br />elevation was set at the 10-year, 24-hour flood elevation. Riprap <br />energy dissipators are provided at the outlet ends of all primary outlet <br />works. The riser configuration is illustrated on Sedimentation Ponds - <br />Kerr Coal Mine Map (Plate I). <br />Rating curves for the riser portion of the emergency spillways and an <br />• example of the entire principle spillway rating curve for Pond E are <br />shown on the Sedimentation Ponds - Hydrology and Hydraulics Map (Plate <br />II). <br />Orifices for each pond were designed utilizing the equation for orifice <br />flow: <br /> <br />Mhere C' orifice coefficient (0.6) <br />a ^ cross sectional area of the inlet (ft=) <br />g ^ gravitational constant (32.2 ft/sect) <br />H height of water above inlet (ft) <br />The design size and the number of orifices used for each pond is <br />summarized in the Pond Schedule on the Sedimentation Ponds - Kerr Coal <br />Mine Map (Plate I). The Sedimentation Ponds Hydrology and Hydraulics <br />. Map (Plate II), contains the riser pipe rating curves. <br />23-42 <br />