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• The sediment storage capacity of each sedimentation pond or impoundment is monitored on an <br />annual basis to ensure that at least one year of sediment storage is available beneath the <br />principal spillway inlet (based on the U.S.L. E. or the equivalent sediment storage of one 10-year, <br />24-hour storm event based on the M.U.S.L.E.). When adequate capacity is no longer <br />available, sediment removal or other corrective actions will be taken to restore adequate <br />sediment storage capacity to the pond. <br />WFC will monitor the sediment storage capacity of each pond with one or a combination of the <br />following methods, as applicable: <br />1. Reference Stake - A reference stake will be set at a predetermined clean-out <br />elevation beneath the principal spillway. When sediment storage reaches this <br />elevation, corrective action would be implemented to restore adequate sediment <br />storage. Reference staking will be utilized in ponds that are normally dry and as an <br />indicator for monitoring personnel as to when a more detailed survey of sediment <br />storage capacity is warranted. <br />2. Cross Sectioning or Grid Method -For the ponds that nonnal{y contain water year <br />round, or where a reference stake could not be detected below the water surface, a <br />survey cross section or grid method will be used to determine sediment volume using <br />• accepted engineering practices. The survey would be performed on an annual basis to <br />determine sediment storage capacity and to determine when corrective action is <br />required to restore adequate pond capacity. <br />3. Aerial Mapping - An alternative method is photogrammetric mapping that would create <br />an accurate 1" = 50' topographic map with 2 ft. contour intervals to determine the <br />remaining storage volume beneath the principal spillway. This method could be used <br />as the sole method for dry ponds or used in conjunction with the surveyed cross <br />section method for ponds partially full of water. Once the topographic map has been <br />generated, accepted engineering methods will be utilized to perform the volumetric <br />calculations. <br />Corrective action required to restore adequate sediment storage capacity may include the <br />following: <br />1. Raise the spillways and redesign the pond in order to restore adequate storage <br />capacity and to comply with the applicable regulations. <br />2. Excavate the ponding area and enlarge the sediment storage capacity. <br />• <br />13-4 <br />