Detention Basin Outlet Structure Modifications

The District has used various approaches to solve stormwater runoff problems experienced by residences and businesses. Typical stormwater problems include overbank flooding from local streams and creeks, flooding along the major river floodplains, street flooding, and erosion along stream and creek corridors as a result of urbanization. In 2000, a Stormwater System Master Improvement Plan (SSMIP) was completed that provided a comprehensive evaluation of the District's policies, procedures, stormwater complaint database, major conveyance systems, streams and creeks, and other watershed characteristics. The SSMIP concluded that the District needed to change the detention standards to not only control peak flow but to also control the volume from runoff events. In addition, the analysis recommended that the detention basins criteria be changed so that the more frequent stormwater runoff events are captured. This recommendation was consistent with citizen comments stating that the existing detention basins within their subdivisions or at a commercial area do not hold any water after a rain event. Thus, the District's regulations were changed for new development but the question remained as to what could be done with detention basins constructed before 1997. A study was undertaken to determine if existing detention basins throughout the District could be retrofitted or modified to accommodate the new standards and mitigate flooding downstream as originally intended.