Improved Extended Detention Basin Performance through Better Residence Time Control

Extended detention basins are not used for stormwater quality management in many areas of the US because they generally do not achieve the 80% removal of total suspended solids required by many regulatory agencies. The objective of the described research was to modify the outlet of an existing basin to provide batch treatment of the runoff and provide more control over the hydraulic residence time., A solar powered automated valve and controller were developed and placed on the outlet of a pond in Austin, Texas in order to increase the detention time beyond the times achievable using an orifice. This allowed all of the diverted runoff to be retained in the basin for a variable preset period of time. The influent and effluent of the pond were monitored for suspended solids, nutrients, chemical oxygen demand, and total and dissolved metals. The suspended solids reductions in the pond were controlled by adjusting the residence time of the runoff in the basin in order to meet the required pollutant reduction. Additionally, the valve can be used to regulate flow into the receiving waters to control peak flow.