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Multimetric Evaluation of Detention Basin Retrofit to Reduce Hydrologic Alteration of Urbanization and Restore Stream Stability
Citation:
Hawley, R., J. Goodrich, J. Beaulieu, K. MacMannis, M. Wooten, C. Frye, E. Fet, AND M. Jacobs. Multimetric Evaluation of Detention Basin Retrofit to Reduce Hydrologic Alteration of Urbanization and Restore Stream Stability. Presented at 9th National Monitoring Conference, Cincinnati, OH, April 28 - May 02, 2014.
Impact/Purpose:
To inform the public.
Description:
Abstract: Conventional stormwater detention basins are ubiquitous in the developed portions of U.S., particularly those areas developed since the 1980s. Because most detention basins were designed exclusively for flood control, they are not being utilized to their fullest potential and do not include measures to mitigate erosive flows from small, but frequent storm events, that are often amplified by urbanization. These underutilized detention basins present a retrofit opportunity to mitigate the erosive energy of small and intermediate storm events without adversely impacting flood control capacity. The purpose of this research was to develop a cost-effective detention basin retrofit device that provides for a more controlled release of storm flows, ultimately mimicking a more natural flow regime. The benefits of this approach can include stream channel protection and water quality improvements (e.g. TSS reductions), as well as stabilization of aquatic habitat in receiving channels. The device is designed to throttle stormwater flow, temporarily detain it, and gradually discharge it to the downstream channel at a more appropriate rate for the receiving stream. To monitor the effectiveness of the retrofit, the project measured an array of multidimensional parameters including: 1) time series rainfall data 2) time series flow data in the detention basin and receiving streams 3) hydrogeomorphic surveys in receiving streams pre- and post- retrofit installation 4) water quality grab samples Preliminary modeling suggests that detention basin residence times will double during the typical year, and that the cumulative duration of flows that cause bed material disturbance in the receiving stream will be reduced by 50% relative to existing conditions. The simple retrofit technology is projected to fully restore the pre-developed disturbance regime, which should improve downstream channel stability and have cascading benefits for water quality, habitat, and ecosystem function. This projected is a collaborative partnership between multiple government agencies (Federal, regional, and local) and private businesses. Monitoring costs were contained by capitalizing on existing data collection efforts by project partners focused on documenting the impacts of urbanization on stream condition, as well as evaluating the performance of green infrastructure and other stormwater BMPs at improving stream health.
