An extended Detention pond relies on 12 to 24 hour detention of stormwater runoff after each rain event; an under-sized outlet structure restricts stormwater flow so it backs up and is stored within the basin.
Wet ponds consist of a permanent pool of standing water that promotes a better environment for gravitational settling, biological uptake and microbial activity.
Constructed wetlands are shallow depressions that receive stormwater inputs for water quality treatment, are typically less than 1 foot deep, and possess variable microtopography to promote dense and diverse wetland cover.
Stormwater filters depend mainly on physical treatment mechanisms to remove pollutants from stormwater runoff, including gravitational settling in the sedimentation chamber, straining at the top of the filter bed, and filtration and adsorption onto the filter media.
Wet swales can provide runoff filtering and treatment within the conveyance system and are a cross between a wetland and a swale.
Dry swales are essentially bioretention cells that are shallower, configured as linear channels, and covered with turf or other surface material (other than mulch and ornamental plants).
Bioretention creates a good environment for runoff reduction, filtration, biological uptake, and microbial activity, and provides high pollutant removal; bioretention can become an attractive landscaping feature with high amenity value and community acceptance.
Infiltration practices use temporary surface or underground storage to allow incoming stormwater runoff to exfiltrate into underlying soils, allowing for a very high runoff volume reduction capability.
Permeable pavement is typically designed to treat stormwater that falls on the actual pavement surface area, but it may also be used to accept run-on from small adjacent impervious areas, such as impermeable driving lanes or rooftops.
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