University of New Hampshire Stormwater Center
2007 Annual Report
About Retention Ponds
General Information Performance Data Water Quality Treatment Process Design
During the first year of operation, the retention pond at UNHSC was reasonably effective in removing many of the pollutants commonly found in runoff. However, during its second year, researchers observed a reduction in its water quality performance. This indicates that its performance may continue to diminish over time.
Back to List of Evaluated Treatments
About Retention Ponds
Retention ponds, or “wet ponds,” are among the most common stormwater treatment systems used today. They are not to be confused with detention basins or “dry basins,” which hold runoff for a specified period of time, and then release the entire volume of the runoff. Retention ponds retain a resident pool of standing water, which improves water quality treatment between storms. Retention ponds demonstrate a reasonably strong water quality treatment, particularly in comparison to dry pond systems. However, lack of maintenance often leads to pollutant export and a gradual erosion within the system for large flows.
Where to Use It
Acceptance of retention ponds is widespread, and examples of these systems can be found all over the world in any climate, soil, and development setting.
In many areas, retention ponds are the system of choice, a preference likely due to their ease of design, which can be adapted to provide water quality treatment and water quantity control in a variety of settings.
While retention ponds are common, their use raises concerns related to human and ecosystem health. Standing water, for example, can be a drowning hazard. They also serve as a habitat for mosquitoes associated with diseases. Ponds that contain excess nutrients can foster eutrophication. In hot weather, retention ponds can super-heat already warm parking lot runoff, impacting aquatic habitats and cold water fisheries. Some innovative retention pond outlet designs include the use of gravel subdrains to cool effluent.
The cost to install a retention pond system to treat runoff from one acre of impervious surface was $13,500. This does not include maintenance expenditures, which may involve routine inspection, periodic mowing, and sediment dredging, as needed. For more information about this design, contact the UNHSC.
Table of Contents
About the Center
About the Field Site
How We Evaluate Performance
Stormwater Treatment Performance Comparison
How to Read this Report
Stormwater Treatment System Data
Resources for Land & Water Management
Download the Report For a Printed Copy Tell Us What You Think
This publication was produced in partnership with the UNH/NOAA Cooperative Institute for Coastal & Estuarine Environmental Technology.