Brent Aigler (Geology) Colby College
Impervious surfaces increase stormwater runoff and sediment flows to recipient water bodies. Efforts to control runoff and sediment transport include the implementation of stormwater detention ponds. The Commonwealth of Virginia has mandated that the two-year peak outflow from a development site cannot exceed its pre-development flow. James City County, VA, also mandated a minimum 24-hour pond detention time for runoff from the one-year, 24-hour storm. My study examined the hydrology and sedimentology of a detention pond located in the Pointe at Jamestown housing development, James City County, VA. Field results demonstrated the pond's inability to reduce the two-year peak outflow to the pre-development level as specified in its engineering designs. Detention times for all twelve storms measured in 2006 were less than 24 hours, even though no storm rainfall reached or surpassed the one-year, 24-hour level. Using engineering data for pond design, the modeled peak inflow, peak outflow, and detention times were significantly lower (p=0.05) than those measured in the field. Three storms were measured during 2006 for sediment input and output, and the Pointe at Jamestown detention pond captured approximately 91% of the 1849 kg of sediment entering the pond through the inflow culvert. Sediment mass input and output values may decrease in the future, as Pointe is still under construction. Sediment concentrations, and ultimately mass yields, tend to be higher during the construction phase and decrease following completion of the development.
For additional documentation Brent Aigler provided a PowerPoint Presentation entitled "A Hydrological and Sedimentological Study of the Pointe at Jamestown Retention Pond" provided here in PDF form.