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• OUTLET MORKS <br />General <br />Riser type outlets were designed for ail five (5) of the proposed ponds. <br />A Type 3 riser constructed of corrugated metal pipe was designed for <br />each of the ponds using a 24-inch vertical riser pipe and an 18-loch <br />conduit. The Type 3 riser has one (1) to three (3) orifices set at the <br />required sedimentation level varying in size for each pond. The <br />orifices serve as the pond's primary outlet, allowing each pond to be <br />dewatered in four (4) to six (6) days. The 24-inch riser invert is set <br />at the crest elevation of the 10-year, 24-hour event plus the <br />groundwater discharge volume. Therefore, there is no discharge through <br />the riser pipe during the 10-year, 24-hour storm. The 24-inch riser <br />pipe serves as the emergency spillway and adequately passes the 25-year, <br />24-hour event maintaining 1.0 foot of dry freeboard between the crest <br />• elevation of the 25-year storm plus groundwater pumping and the design <br />elevation of the pond embankment. An expanded metal trash screen will <br />be installed on each riser pipe and riprap energy dissipators will be <br />provided at the outlet ends of all spillways. The riser configuration <br />is shown on the Proposed Pond and 01tch Design Map. (Map 23-1). This <br />map also contains a pond schedule summarizing the design of the primary <br />and emergency spillways for each pond. <br />Primary Outlet Design <br />The SEDCAD+ computer model utilizes the equation for orifice flow to <br />calculate discharge through the primary outlet as follows: <br /> <br />Where: C' orifice coefficient (0.6) <br />a =cross sectional area of inlet (ft=) <br />g =gravitational constant (32.2 ft/sec=) <br />H =height of water above inlet (ft) <br />23-143 <br />