Slide 36 of 43
Notes:
The design approach for sizing filter strips is based on temporarily storing the WQv within a shallow ponding area. This methodology also utilizes a volume based sizing criteria for the WQv.
The size of the filter strip is determined by the required treatment volume, however the minimum length must be 25 feet. The width of the filter strip is equal to the width of the area draining to it. The maximum slope should be no more than 6.0% and the minimum slope should be no less than 2.0%. Steeper slopes will increase velocities and lead to concentration of runoff and likelihood for erosion. In addition, as the slope increases, the treatment volume per cross sectional area decreases. The maximum drainage area to filter strips is limited by the overland flow limits of 150 feet for pervious surfaces and 75 feet for impervious surfaces.