Traditional stormwater management strategies focused on conveyance and detention. Storm sewers were designed to move stormwater off urban landscapes to detention basins to reduce downstream flooding. The Iowa Stormwater Management Manual provides new stormwater management strategies that compliment the conveyance and flood control efforts of the past. The manual provides information on hydrologic changes with urban development, uniform sizing criteria, low impact development alternatives and design guideline for practices that protect water quality and reduce stream corridor erosion.
Historically, 90 percent of annual rainfall has been from events that are less the 1.25 inches. A primary focus of the manual is to provide design guidelines for practices that infiltrate small runoff events to protect water quality. The manual also provides design guidelines for stream corridor protection, which is important because stream corridor erosion causes up to 70 percent of sediment loading in urban areas. These practices provide significant water quality benefits, and protect pipelines, sanitary sewers and other infrastructure. Adding water quality and channel protection practices to traditional conveyance and flood control practices will make our stormwater management strategies more holistic and effective.