Extended Detention Basins Use Technology to Offer New SolutionPosted on Wednesday, February 13th, 2019 by Brad Schleeter
In Stormwater, tagged in
The complexity and benefit of stormwater basins varies to meet the specific design intent of a project. If reducing peak flow rates to existing conditions is the priority, a dry detention basin should be considered. If downstream channel stability is a concern, an extended detention basin should be considered. Or, if improved water quality is the goal, a wet detention basin should be considered.
Dry detention basins are prevalent in this part of the country. The detention basin bottom is typically grass lined, often designed with a concrete or riprap low flow channel across the bottom to limit standing water in the basin and reduce erosion within it. The primary purpose of dry detention basins is flood control with minimal water quality benefits.
Wet detention basins are designed to improve water quality and can also provide flood control benefits. These basins maintain a permanent pool of water, providing a means to settle out pollutants, while offering the aesthetic benefit of a water feature. Wet detention basins can also have a restricted outlet in order to limit peak discharges from the pond for flood control.
Extended detention basins can be designed as either a dry or wet basin that features a multi-stage outlet. They can provide the same benefits as a dry or wet detention ponds, but come with the a greater ability to manage discharge from a range of storm events. Small storms can be restricted to a rate that mimics stream baseflow conditions. More significant storm events can be controlled by a larger outlet pipe behind a weir wall to maximize the basin volume for flood control.
In general, dry, wet, and extended detention basins operate with a fixed outlet that maintains a static water level within the basin. However, new technology that uses real-time monitoring and outlet controls to provide basin owners with a greater ability to manage discharges, water levels, and storage capacity in real-time maximizes the flood control and water quality benefits of the basin. This new proprietary technology being used locally continuously monitors basin available storage volumes and weather forecast data. Real-time controls operate valves that can hold back or release ponded water slowly depending on the rain forecast. Using this approach helps to improve the overall water quality performance of a basin, as water is detained for a longer period of time, or if a rain event is in the forecast, the basin could be drained down to fully capture the “first-flush” rain event that generally carries the highest pollutant loads. Benefits can also be experienced by channels downstream, as the flow can be better regulated to mimic a natural base flow.
Before implementing this new real-time technology, there are a few items to consider.
- The upfront cost to install the new technology and potentially retrofit the existing basin outlet.
- The ongoing cost for monitoring and forecast service subscription.
- Long-term inspection and maintenance requirements with a more complicated outlet and equipment.
- The basin must be a certain minimum size to experience the benefit and justify the added cost and long-term commitment to the new technology.
With the right application and a commitment to the upfront investment and long-term responsibility, this new real-time technology has great promise for improving the performance of stormwater basins.