The Effectiveness of Dry and Wet Stormwater Detention Basins As Sediment and Nutrient Processors

Urban sprawl places watersheds and associated streams and rivers under increased stress in terms of impaired water quality from stormwater runoff. This study investigated the response of one wet and two dry stormwater detention basins to rainfall events to determine their effectiveness as sediment and nutrient processors. The study was conducted in James City County, Virginia, a county presently experiencing rapid residential and commercial growth. Using automated ISCO© water samplers, samples were collected before, during, and after rainfall events of variable magnitude. Samples were analyzed for the following: dissolved inorganic phosphorus, total particulate phosphorus, dissolved nitrate+nitrite, dissolved ammonium, total suspended sediment (TSS), and total dissolved sediment (TDS). Significant increases in nutrient concentration and sediment discharge from both wet and dry detention basins were observed during and after rainfall events. Dry detention basins, however, were less effective than wet basins in processing sediment and nutrient concentrations during the three separate rainfall events. In James City County there has been a recent policy push to install wet detention basins rather than dry basins. These data support such a change in stormwater management practices to maintain better water quality in developing watersheds.