Document Type

Thesis

Abstract

Increased stormwater runoff associated with urbanization arrives at streams faster than in pre-development conditions due to increased impervious cover, decreased infiltration rates, and man-made drainage systems (Leopold, 1968). This can generate higher peak discharges, longer duration of bankfull flows, increased erosion/sediment yield, and greater threats of flooding for similar sized storm events (CWP, 2003). The wet retention pond is a Best Management Practice that is designed to mitigate for these changes by holding a permanent pool of water and releasing stormwater runoff slowly over time in order to reduce post-development peak discharges. Though these ponds are widely used there is little to quantify their effectiveness; this study aims to determine the effectiveness of a wet retention pond in the Pointe at Jamestown neighborhood in James City County, VA. Pond surface elevation readings were recorded on a fifteen minute interval by a pressure transducer set at a fixed elevation in the retention pond from June 2005 to April 2006. Discharge rates and cumulative outflow volumes were calculated by using the design model discharge equations with the measured pond elevations. Elevation measurements were also converted to pond storage to determine changes in volume, inflow rates, and retention times. Though none of the recorded twenty-one storm events approached the size of a 2 yr, 24 hr storm (3.5” of rainfall), the 2 yr, 24 hr design outflow value (.96 cfs) was exceeded five times and the inflow rates were relatively high. The retention time of the inflow was less than 13 hours for all of the fifteen fully analyzed storms; seven storms had retention times of less than 5 hours. The runoff coefficients for all fifteen storms were all close to the design coefficient of .4, but at the time of this study, the Pointe at Jamestown development was only 50% complete.

Date Awarded

2006

Department

Geology

Advisor 1

Gregory S. Hancock

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