CCP 02-10-1992 - Laserfiche WebLink

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I .. The wetland preservation area currently acts as a storm water detention I 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 I year 24 hour storm. Therefore. an overflow must be provided to prevent the I pond level from increasing to an elevation of approximately 973.0 which is the level at which the water floods the surrounding property. I The outlet from the pond serving the drainage area. which is approximately I 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 I feet per second (cfs). to the pond designated as pond A-7a. By installing a I 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 I develop full flow in the pipe. I A baffled weir is required by the Rice Creek Watershed District to treat the I 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 I water into the 24" RCP pipe. The baffled wier forces the debris, leaves and I other suspended solids to settle into the pond. thereby cleaning the runoff before discharge. The baffled weir for the wetland preservation area is I 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 weir through the rock creating a pond that will be relatively dry. I I