Detention ponds are a Best Management Practice (BMP) implemented to reduce peak runoff rates and control water quantity. This sustainable strategy may be used as a means to avoid the expense and environmental impact common with conventional stormwater management systems, such as drain inlets and culverts, which typically deliver runoff to adjacent watersheds without any filtration. Detention ponds are an effective method to remove sediment and pollutants from stormwater as well as reduce peak runoff rates in an effort to prevent flooding and erosion of local waterways. If implemented with the overall landscape design, cost of detention ponds can be kept to a minimum since construction methods and materials are similar to standard landscaping practices.

Two types of detention ponds, wet and dry, may be implemented based on the desired results. Wet detention ponds have a permanent pool of water, while dry detention ponds detain water for a predetermined amount of time based on the design and size. Both of these methods contain the same basic elements: a water detention area and an outlet device which slows the runoff to predevelopment rates.

Wet detention ponds have a permanent pool of water in order to allow gradual removal of suspended solids through sedimentation and biological uptake. In addition to superior water quality control as compared to dry retention ponds, wet detention ponds may also be designed to add aesthetic value or serve as an AT/FP buffer.

Figure 1. Wet detention pond design detail

Applicability of a wet detention pond will vary depending on site specific characteristics. Highly developed areas may not be feasible due to the lack of available land required for the ponding area however wet and dry detention ponds may be implemented as an end-of-pipe treatment method. Arid climates may also exclude this stormwater mitigation method because of the need for a constant presence of water.

In sharp contrast to wet detention ponds, dry detention ponds typically retain stormwater runoff in the range of twelve to forty-eight hours. This stormwater mitigation method is effective for flood control and erosion prevention of local waterways; however, it does not have soluble pollutant removal properties equal to wet detention ponds due to the limited amount of time water is detained. Small, separate ponding areas may be employed at the inlet and/or outlet of the detention pond to increase the runoff storage capacity as well as the pollutant and sediment removal capability.

Dry detention ponds have successfully been used to control stormwater runoff in a variety of locations across the world. Sufficient space for the detention pond and the size of the drainage area to be controlled are the most important deciding factors. Both dry and wet detention ponds have been shown to increase stormwater temperatures, therefore, careful consideration needs to be taken if the pond will be feeding into a cold water habitat.

                                Figure 2. Dry detention pond design detail

Both wet and dry detention ponds are potential strategies to achieve the intent of LEED SS Credit 6.1 and SS Credit 6.2. Refer to the LEED Guidance section for specific requirements.