Regenerative Stormwater Conveyance Provides Needed Treatment for Runoff Volume, Peak Discharge, and Quality Control for New Development or Retrofitting Underserved Watersheds

摘要

Stormwater conveyance practices are grounded in industrial design that neglects integration withrnsystem processes, economics, and aesthetics. As a result, the greater volume of runoff from imperviousrnsurfaces, coupled with smooth and hardened conveyance systems (e.g., pipes and trapezoidal concreternchannels), magnifies and transfers energies to the discharge or outfall. Conventional stormwaterrnoutfalls cause erosion, conveyance structures fail, receiving stream channels are degraded, in-streamrnsedimentation increases the influence of localized erosion upstream and downstream of the outfall, andrnan increasing spiral of degradation results. Local governments are forced to spend scare public funds onrnremediation measures. Alternatively, using stream restoration techniques to create a dependable openrnchannel conveyance with pools and riffle grade controls is a regenerative design since the use of thesernelements result in a system of physical features, chemical processes, and biological mechanisms that canrnhave dramatic positive feedback effects on the ecology of a drainage area. This approach results in therndelivery of low energy storm water discharge, potential volume loss through infiltration and seepage,rnincreased time of concentration as a result of increased roughness and storage along the flowpath,rnincreased temporary water storage, restoration of lowered groundwater, increases in vernal poolrnwetland area, improved water quality treatment, improvements in local micro-habitat diversity, andrnprovides a significant aesthetic value. These projects are generally a win-win-win arrangement, asrnconventional construction practices and materials are more expensive, conventional conveyancernprovides no environmental benefits and are more difficult to permit, and people generally enjoy thernaesthetics associated with a well vegetated channel form when compared to the conventionalrnconveyance alternative. This approach has been adopted in Maryland’s draft NPDES guidancerndocument (Maryland Department of the Environment 2011)