ENVIRONMENTAL CONNECTION / THIRD QUARTER 2025 / IECA.ORG 15 finer sediment particles to settle. This initial treatment facilitates access for maintenance, which allows sediment to be removed more frequently without the use of heavy machinery. Part Two: Basin (Settling Pond) The preferred shape of a sediment basin is rectangular; however, depending on site conditions and topographic restraints, different shapes may be employed. Designing a basin with a length-to-width ratio of 2:1 or greater will create a longer flow path from the inflow to the outflow of the basin, which gives more time for settling to occur before off-site discharge. As with the inflow channel, stabilization of the inlet and the side slopes will prevent increasing turbidity levels from erosion occurring in the basin. The volume of the basin is split into different zones. At the bottom of the basin is a standing pool, a permanent volume of water designed not to dewater but only to infiltrate or evaporate. This pool serves to detain the water with the highest concentration of sediment for an extended period, which allows for additional sedimentation to occur. This process also serves to slow water as it enters the basin, which reduces turbulence and the risk of resuspension of already-accumulated sediment in the basin. Above the standing pool is the stormwater storage, which is the volume of the basin designed to be dewatered by the primary dewatering device. This volume should be 3600 feet3 (102 m3) per acre of the total drainage area of the site or designed to handle a two-year 24-hour storm, and it extends from the elevation of the primary outlet to the bottom of auxiliary spillway. At the top of the basin is additional storage designed to discharge over the auxiliary spillway when flow rates and/or flow volume are beyond the capacity of the primary dewatering device. This storage should be designed to handle a 10-year 24-hour storm peak flow rate. Lastly, designing some freeboard above the auxiliary spillway volume allows for water to be contained within the basin and not overflow during heavy storms. >> EROSION CONTROL PEER REVIEW Figure 2. A series of three porous baffles configured perpendicularly to flow from the inlet to the outlet.
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