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I~ -6- <br />I Pond .A, a 48-inch reinforced concrete pipe (RCP) riser and a 36-inch conduit <br />under the embanivoent were selected. The riser pipe will have six sets of <br />I four 5-inch diameter holes spaced at 1'~-feet along the riser from elevation <br />6930 to 6938.5. For Ponds D, E, F, and G, a Type 2 riser was designed. It <br />I will be constructed of corrugated metal pipe (CHIP) and have sets of four fl- <br />inch diameter holes at two-foot spacing, beginning at specified elevations <br />and extending along the riser height. For the remainder of the ponds, a <br />I Type 3 riser constructed of CMP was designed. The Type 3 riser has only one <br />or two holes whose size and elevation vary for each pond. The risers are <br />I detailed on the LRCWE Plate I, Sedimentation Ponds, Energy Pfines No. 1 and <br />2, and Eckman Park. For Sedimentation Pond A, the riser elevation was set <br />I at one-half foot above the routed 10-year flood elevation. In addition to <br />the riser holes, Pond A is provided with a 12-inch gated outlet at elevation <br />I 6920 feet to allow release of stored irrigation water. For all of the other <br />ponds, the riser crest elevation was set at 0.1 foot above the 10-year flood <br />elevation. <br />J <br />The LRCWE Plate I Sedimentation Ponds, Energy Mines No. 1 and 2, and Eckman <br />Park gives rating curves for the riser portion of the principal spillways <br />for riser Types 1, 2, and 3. It also shows examples of the entire principal <br />spillway rating curves for Ponds D and R which have Type 2 and Type 3 risers, <br />respectively. <br />1 Emergency Spillways <br />I In accordance with 30CFR816.46 (i), the 100-year 24-hour precipitation event <br />was used to size the emergency spillway for each pond whose height (as mea- <br />l sured from upstream toe of embankment to emergency spillway) exceeded 20 <br />feet, or whose storage volume exceeded 20 acre-feet. For those ponds not <br />exceeding this criteria, the 25-year flood was utilized. In all cases, the <br />l emergency spillway crest elevation was set at one-foot above the riser crest <br />elevation. For Pond A, a S-foot diameter RCP was selected as the emergency <br />I spillway because [he planned haul road immediately downstream from the dam <br />would not allow a weir type overflow. For all of [he other ponds, a weir <br />Permit Renewal No. 3 Exhibit 8q 1/IS/00 <br />Page 8 of 22 <br />