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| US Department of Environmental Quality,
2002. |
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Description
Small body of water designed to collect storm water runoff for a designated
duration of time providing pollutant removal and flood control. The extended
resting period allows for settling and nutrient uptake to achieve pollutant
removal.
Mechanisms
Pollutant removal is achieved through a variety of processes including
sedimentation, biological uptake, adsorption, flocculation and minimal amounts
of infiltration and evaporation.
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| Metropolitan Council of Minnesota, 2003. |
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Applications
- Useful in reducing runoff contamination from large impervious surfaces.
- Recommended for treatment areas greater than 10 acres.
- Suitable for high pollution concentration runoff sites if sufficient
separation from groundwater.
- Not for use with steep slopes.
- Requires a large amount of land area.
- Requires high runoff rates or other water sources to maintain pond level.
- Not recommended for arid climates.
- Can be implemented downstream of the runoff source.
- Can result in warm water outputs.
- Requires pretreatment for suspended solids removal.
- Cold climates may require excess planning.
- May require obtaining permits.
Detailed Specifications
Design Values*:
- Control 2 and/or 10-year storm events and pass a 100-year storm event.
- Calculate the hydraulic residence time using the eutrophication method or
the solid settling method to determine desired removal efficiency.
- Calculate the pond dimensions based on the hydraulic residence time, most
importantly the volume and depth.
- Larger permanent pool volume to mean storm runoff volume ratios increase
pollutant removal.
- Maximum depth of 20 feet, optimal 3-9 feet.
- Common length to width ratio of 2:1, the smaller the ratio the greater the
treatment.
- Shoreline slopes between 5:1-10:1.
- Minimum side slopes of 2:1.
- Minimum embankment top width of 6 feet for maintenance purposes.
- Plant aquatic and wetland vegetation.
- Maximum slope 15%.
- Install sediment forebay.
- Greater pool sizes increase pollution removal, but the runoff area must be
able to sustain the permanent pool.
- Install a vegetated ledge to provide a habitat for plant growth.
- Soil permeability of 10-5-10-6 cm/s to maintain
permanent pool.
- Install a riser and release pipe at the outlet to control flows.
- Install spillway for storm events exceeding capacity.
- For more information visit:
Metropolitan Council of Minnesota Urban Small Sites Best Management Practices,
US EPA Wet Detention Pond
Storm Water Technology Fact Sheet,
US EPA
Wet Ponds Post-Construction Storm Water Management in New Development &
Redevelopment.
*Note: Local governments may use different design values
than those listed above, be sure to comply with any applicable laws and
regulations.
Plans
Maryland Department of the Environment, 1986 (Cited in Metropolitan Council of
Minnesota, 2003).
Schueler, 1987 (Cited in Metropolitan Council of Minnesota, 2003).
Water Quality
Maintenance
- Dredge sediment forebay as needed.
- Dredge permanent pool every 2-7 years.
- Remove any debris or garbage as needed.
- Control mosquito growth.
- Monitor hydrocarbon buildup, manage when necessary.
- Manage vegetation.
- Repair erosion.
- Remove any nuisance vegetation as needed.
- Always maintain permanent pool depth.
Resources
Maryland Department of the Environment, Sediment and Storm Water
Administration. 1986. Feasibility and Design of Wet Ponds to Achieve Water
Quality Control.
Metropolitan Council of Minnesota. 2003. Wet Ponds. Urban Small Sites
Best Management Practice Manual. pp. 3-251 - 3-265.
http://www.metrocouncil.org/environment/Watershed/BMP/CH3_STRetenWetPond.pdf
(January 2006).
Schueler, T. 1987. Controlling Urban Runoff: A Practical Manual for Planning
and Designing Urban BMPs. Metropolitan Washington Council of Governments.
United States Environmental Protection Agency. September 1999. Wet Detention
Ponds. Storm Water Technology Fact Sheet. EPA 832-F-99-048.
http://www.epa.gov/owmitnet/mtb/wetdtnpn.pdf (February 2006).
United States Environmental Protection Agency. August 15, 2002. Wet Ponds.
Post-Construction Storm Water Management in New Development & Redevelopment.
http://cfpub.epa.gov/npdes/stormwater/menuofbmps/index.cfm (February
2006).
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