Storm Water Extended Release for Low Impact Development

Storm water detention has been widely used for on-site runoff release control. The required storm water detention volumes are often determined by the pre-selected release rates for various design events. When a low release rate is selected, the basin stores more storm water volume than required and it results in an insufficient base flow for the downstream habitats. When a high release is selected, the prolonged basin operation may cause erosion to downstream stream bed and banks. Balancing the tradeoffs, this paper presents a method by which the required detention volume can be determined by urbanization retrofits. The method considers the change of imperviousness, design rainfall depth, watershed hydrologic losses as the design factors. Although the procedure is simple, it well agrees with the design criteria derived from sophisticated computer simulations.