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A retention pond is a basin that is designed to catch runoff water from higher elevation areas. Retention ponds are used to prevent or minimize flooding during high water periods. These basins are usually designed with an overflow pipe to control water levels and disperse water evenly.
Typically shallow, retention ponds usually have slow, sloping floors. They rarely take up much land and average less than 1 acre (4046.86 m2) in total size. Most ponds are built in areas that have surrounding land capable of accommodating high water during rainy periods. Allowing for excess surrounding land is considered essential for proper function and safety.
Developing a retention pond will serve to remove pollutants and reduce flooding. The ponds may serve as temporary or permanent runoff basins, and it is very common to find them in areas that are undergoing significant amounts of construction. This is due to the fact that large areas consisting of impermeable surfaces will not properly absorb water during rain fall.
Permanent ponds are often built in lower land areas that tend to accumulate excess amounts of water. Retention ponds aid in the removal of pollutants, as trash and debris typically run into the pond after heavy rains. The basins also catch runoff containing petroleum, fertilizers, sediments, bacteria, and other harmful substances that may have negative impacts on overall water quality.
As pollutants enter the pond during a heavy rain, the basin works to slow water movement. The stagnant water allows heavier contaminants, such as solids or metals, to sink to the bottom of the pond and eventually become bottom layer sediments. The retained water naturally filters contaminants and returns clean water to nearby streams or wetlands.
A retention pond located in a residential area may present safety concerns and certain measures of precaution should be taken. While the ponds are fairly shallow, they usually average 8 to 10 feet (2 to 3 meters) in depth and should by no means be considered an area for recreation or swimming. The banks of retention ponds are typically built with shallow banks and then drop sharply after about 2 feet (.5 meter) of shallow water. The shallow banks are developed as a safety measure to prevent drowning, but children should still be kept away from the pond and surrounding areas. These areas are also potentially dangerous due to the level of contaminants that accumulate in stagnant water.
In order to preserve a safe and effective retention pond, it must be properly maintained. Adding a waterfall or aerator may help keep mosquitoes and other pests from breeding excessively around the pond. A pest control specialist may also alleviate insect issues by adding a natural larvacide to a pond. Algae overgrowth is another potential concern, and it may be necessary to contact an aquatic management specialist to provide the proper bacteria and microbes for the pond.
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