CCP 01-13-1992 - Laserfiche WebLink

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. The wetland preservation area currently acts as a storm water detention basin. It was not designed for the purpose of storing runoff, because this area is not sized adequately to detain 1.8 acre feet of runoff from the 100 year 24 hour storm. Therefore, an overflow must be provided to prevent the pond level from increasing to an elevation of approximately 973.0 which is the level at which the water floods the surrounding property. The outlet from the pond serving the drainage area, which is approximately '- 6.8 acres, will be a 24 inch diameter reinforced concrete pipe. This pipe will convey the peak flow from a 100 year 24 hour storm, equal to 22 cubic feet per second (cfs), to the pond designated as pond A-7a. By installing a 24" pipe, the pond elevation will not rise above 972.80 while discharging the peak flow. The size of the wetland preservation area is not a factor in . sizing the pipe and determining the elevation of the pond. The 24" RCP storm sewer requires 3.2 feet of water above the invert of the pipe to develop full flow in the pipe. A baffled weir is required by the Rice Creek Watershed District to treat the increased volume of runoff from a 1 year 24 hour storm that is directed into the wetland preservation area by removing the solids before outletting the water into the 24" RCP pipe. The baffled wier forces the debris, leaves and other suspended solids to settle into the pond, thereby cleaning the runoff before discharge. The baffled weir for the wetland preservation area is shown on page 4 of the plans. The baffled weir design will begin to treat the water in the pond when it rises to elevation 970.2, therefore ponding 0.7 feet of water. This water level Will eventually drain under the baffled c. weir through the rock creating a pond that will be relatively dry. , . ~ .