System Description Sample Clauses

System Description. The wet detention basin is designed to trap 80% of sediment in runoff and maintain pre-development downstream peak flows. The basin has two forebays (smaller ponds) located at the low end of two grass ▇▇▇▇▇▇. In addition to runoff conveyance, the grass ▇▇▇▇▇▇ also allow infiltration and filtering of pollutants, especially from smaller storms. The forebays are each 4 feet deep. They are connected to the main pool by 18 and 24-inch metal pipes that outlet onto a rock chute. The forebays will trap coarse sediments in runoff, such as road sands, thus reducing maintenance of the main basin. The main pool will trap the finer suspended sediment. To do this, the pond size, water level and outlet structures must be maintained as specified in this Agreement (see Figures 1, 2 and 3). The main basin receives runoff from a 67.1 acre drainage area (41.2 acres within the subdivision and 25.9 acres off- site drainage coming from the east). During high rainfall or snow melt events, the water level will temporarily rise and slowly drain down to the elevation of the control structure. The water level is controlled by a 12-inch concrete pipe extending through the berm in the northwest corner of the basin (see Figures 1 and 3). On the face of the 12- inch pipe, there is metal plate with a 3-inch drilled hole (orifice) with stone in front of it. This orifice controls the water level and causes the pond to temporarily rise during runoff events. Washed stone (1-2” diameter) is placed in front of the orifice to prevent clogging. High flows may enter the grated concrete riser or flow over the rock lined emergency spillway. “As-built” construction drawings of the basin, showing actual dimensions, elevations, outlet structures, etc. will be recorded as an addendum(s) to this agreement within 60 days after Waukesha County accepts verification of construction from the project engineer.