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Ditch designs are summarized in Figure 1, Permanent Ditch Design Summary. <br />Ditch locations are shown on the Postmining Drainage and Sediment Control Map, <br />(Map R-1). <br />Pond 4 <br />The proposed slope reduction activities east of Pond 4 will reduce pond capacity. <br />The new pond configuration will meet all requirements for sediment ponds in <br />accordance with Rules 4.05.6 of the CMLRD Rules and Regulations. The outlet <br />structure has been designed to safely pass the peak discharge from the 25-year, <br />24-hour event while providing at least 1 foot of freeboard. <br />Pond 4 will employ a 30-inch diameter CMP barrel extending through the pond <br />embankment with a 4" gated decant as the primary outlet structure. The gate will <br />remain open until effective runoff control is reestablished for the contributing <br />drainage area. Pond 4 will utilize a riprapped trapezoidal channel with a 5 foot <br />• bottom and 3H:1 V sideslopes as an emergency spillway. The pond design and <br />stage/storage curve are shown on the Pond 4 Design Map (Map R-3). The <br />- stage/storage curve illustrates sediment and runoff storage capacity. The <br />following summarizes the revised Pond 4 design: <br />Three-Year Sediment Yield (ac-ft) 0.35 <br />Elevation Three-Year Sediment (ft) <br />Elevation Gated Decant (primary outlet) , <br />Volume 10-year, 24-Hour Event (ac-ft) <br />Volume Runoff and Sediment (ac-ft) <br />Elevation 10-year, 24-hour Event (ft) <br />Elevation Emergency Spillway Invert (ft) <br />Elevation Maximum Water Level 25-year, 24-hour Event (ft) <br />Elevation Top of Structure (ft) <br />Freeboard (ft) <br />• <br />7539.6 <br />7539.6 <br />2.57 <br />2.92 <br />7547.5 <br />7547.6 - <br />7548.6 <br />7550.00 <br />1.4 <br />7 <br />17 <br />