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• <br />As -built erodible channel (below spillway) available freeboard = 0.95 feet <br />Downstream Vegetated Spillway Channel (immediately downstream from <br />Perimeter Drainage Ditches) <br />Vegetated channel (below spillway) velocity = 0.7 fps <br />Vegetated channel (below spillway) limiting velocity = 5.0 fps <br />Vegetated channel (below spillway) maximum discharge = 6.990 cfs <br />Vegetated channel (below spillway) maximum water depth = 0.74 feet <br />As -built vegetated channel (below spillway) available freeboard = 0.46 feet <br />spillway with Erodible <br />Table 3. Summary of Pertinent Pond Depth, Elevation, Area, and Volume Data <br />Depth <br />Elevation <br />Area <br />Water <br />Runoff <br />Comments <br />(feet) <br />(feet) <br />(acres) <br />Storage <br />Volume <br />Capacity <br />(acre -feet) <br />acre -feet <br />-0.04 <br />6,730.52 <br />0.000 <br />0.000 <br />Pond empty w/o <br />sediment <br />0.00 <br />6,730.58 <br />0.050 <br />0.000 <br />Pond with 3 yrs <br />sediment (0.003 ac -ft) <br />1.87 <br />6,732.45 <br />0.382 <br />0.4638 <br />Maximum starting pool <br />elevation with capacity <br />to still contain 10 -yr, <br />24 -hr runoff without <br />spilling <br />2.72 <br />6,733.20 <br />0.442 <br />0.782 <br />0.782 <br />Pond with 3 yrs <br />sediment (0.003 ac -ft) <br />plus 10 -yr, 24 -hr runoff <br />volume (1.0 ft of <br />freeboard remaining to <br />spillway) <br />3.62 <br />6,734.20 <br />0.492 <br />1.246 <br />Spillway invert <br />4.03 <br />6,734.61 <br />0.518 <br />1.449 <br />1.0279 <br />Pond full to top of <br />spillway invert plus 25- <br />yr, 24 -hr runoff volume <br />(maximum spillway <br />entrance depth is 0.41 <br />ft; spillway freeboard is <br />1.08 ft) <br />5.11 <br />6,735.69 <br />0.566 <br />2.036 <br />Top of natural <br />ground /settled pond <br />embankment <br />Rainfall Dewatering <br />During and following any major precipitation runoff event, inflows will first fill any unused sediment and <br />dead storage capacity, and will then begin discharging through the emergency spillway. The pond will <br />dewater to the spillway invert elevation within a relatively short time after runoff ceases. It is anticipated <br />that evaporation will further reduce water levels until the next precipitation event occurs. Even without <br />further dewatering, the pond in its full state will adequately treat the runoff from subsequent or back -to- <br />back 10 -year, 24 -hour events. <br />TCC 6MN Intake Shaft Facility 7 <br />Drainage and Sediment Control System Design <br />Water & Earth Technologies, Inc. <br />April 24, 2009 <br />