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Evaluation of the Performance of a Stormwater Detention Pond

Joel Nipper, current Doctoral dissertation research project in Natural Resources at the University of Vermont

Englesby Brook project

Development of land cover creates impervious surfaces into which water cannot easily infiltrate. The excess runoff generated when rain falls on impervious surfaces can cause degradation of water quality when discharged into surface waters. One of the most common storm water treatment practices used to mitigate the harmful effects of runoff from developed lands is the storm water detention pond.

These basins, built to capture and temporarily store the excess runoff generated by storm events, gradually release the water over time. This temporary storage reduces the delivery of increased runoff volume to downstream locations, thereby reducing both the risk of flooding and the level of disturbance in streams. Also, a combination of physical and biological processes removes some pollutants during the period of storage within the pond.

While all functioning detention ponds can be expected to provide some degree of peak flow attenuation and pollutant removal, the performance of any specific structure will depend on the pond's design, the characteristics of the area contributing runoff to the pond, and the degree to which the pond is properly maintained. Pond performance can also be expected to vary seasonally and regionally. For example, hotter temperatures may enable a greater degree of biological removal, whereas the presence of ice in a pond may obstruct flow and decrease performance.

Detention ponds are a significant component of Vermont's efforts to improve water quality in 17 watersheds that have been determined to be impaired as a result of storm water discharges. Despite the prevalence of storm water ponds in the landscape, little research has been done in Vermont on the actual performance of large, modern-design detention ponds.

This research effort is designed to determine (a) how efficient a large storm water detention pond is at removing total nitrogen, total phosphorus, and sediment from runoff and (b) how effective that pond is at remediating storm water hydrology in a whole watershed context.

To answer these questions, we have been measuring flow and determining water quality at a large detention pond in the Englesby Brook watershed in Burlington, VT. Sampling began in 2007 and will continue through 2009, providing a large set of water quality data across seasons and under varying flow conditions. Jamie Shanley and others from the USGS Vermont Field Office are collaborating on this effort.

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Last modified October 16 2009 12:35 PM

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