A detention pond is a basin that lies in a low area near a river or stream and is designed to protect areas from flooding. Dry detention ponds are generally used to hold over-flow water temporarily until it drains into another location. Wet detention ponds manage storm water by maintaining a permanent pond of water in a basin that removes pollutants and only drains partial amounts storm water.
Dry detention basins are the most common type of detention pond. These dry ponds can help control flood waters, prevent downstream channel scouring and may help reduce pollutants. Dry detention ponds also tend to require less maintenance and cost less than other detention pond alternatives.
After a rainstorm, dry detention ponds slowly release collected water into culverts. The water releases slowly through a pipe installed at the lowest area of the basin. The water may then run down to other land areas or into a nearby water source, such as river or stream.
A dry detention pond is typically found in suburban areas containing high amounts of concrete that affect the natural water run-off process. Curb-side drains will often empty into a dry detention pond located in a remote area, usually close to a natural water source. A well-designed basin will help to avoid the common occurrence of slow draining and clogging at inlets and outlets.
Wet detention ponds may cost more to build and maintain than dry ponds, but they tend to be more aesthetically pleasing, conducive to wildlife habitation, and in some cases, they may be more effective. These ponds tend to resemble standard man-made lakes and are surrounded by natural vegetation. A wet detention pond serves to relieve flooding in lower areas but may also improve water quality and naturally reduce pollutants.
A wet detention pond works similarly to a dry pond by collecting water flow from drainage systems. The wet detention ponds tend to hold water for a much longer period of time and drain more slowly. These structures will release water into a nearby water source, but only in the event of a major storm.
Surrounding vegetation is an important component to the structure of wet detention ponds. Vegetation may help remove soluble water nutrients and improve bank stability. A high bank that is covered in vegetation provides a safety shelf. This shelf not only protects against flooding, but also reduces the risks of drowning accidents.
In order for wet detention ponds to function properly, they need a fair amount of maintenance. The pond should be inspected regularly to make sure the proper water levels are maintained and that the water is not accumulating algae or bacteria. The sediments will also need to be removed from the bottom of the pond every couple of years.