Laserfiche WebLink
I~ <br />Section 816.46(h) Continued. <br />Sediment will be removed from all sedimentation ponds when the volume <br />of sediment accumulates to not greater than 60 percent of the design <br />sediment storage volume. A staff gage installed in each pond will <br />allow periodic measurements of sediment accumulation. Ponds will be <br />cleaned out when necessary, usually during the late summer months <br />when Lhe water levels are lowest or during the winter when the ground <br />is frozen. The removed sediment will be disposed of in backfill <br />areas. <br />(i) An appropriate combination of principal and emergency spillways shall <br />be provided to safely discharge the runoff from a 25-year, 24-hour <br />precipitation event, or larger event specified by the regulatory <br />authority. The elevation of the crest of the emergency spillway shall be <br />a minimum of 1.0 foot above the crest of the principal spillway. <br />M Emergency spillway grades and allowable velocities shall be approved by <br />the regulatory authority. <br />All ponds have been designed to provide for a minimum 1.0 foot <br />freeboard between the crest of the principal spillway and the crest <br />of the emergency spillway. The crest of the principal spillway is <br />the dewatering elevation of the drain holes in the riser. The crest <br />of the emergency spillway is the dewatering elevation of the weir- <br />~ type spillway or conduit pipe, whichever is used. Emergency spillway <br />design grades and velocities are provided for each pond in Exhibit <br />42, Drainage and Sediment Control Plan. <br />(j) The minimum elevation at the top of-the settled embankment shall be <br />1.0 foot above the water surface in the pond with the emergency spillway - <br />flowing at design depth. For embankments subject to settlement, this <br />816-54R <br />Revised - January, 1991 <br />