Retention ponds are excellent for removing the trash and pollutants from the runoff. Because it is a controlled body of water, the retention pond captures the trash and debris, and pollutants have a chance to settle out of the water. Because a wet pond is like a living organism, harmful substances such as petroleum products, fertilizers, sediments, bacteria, and metals can safely be separated from the potable water.
The algae, bacteria, and other biological processes in the retention pond can safely consume the pollutants and purify the water to a large degree. Cities, towns, and other municipalities increasingly need a way to manage the runoff at construction sites and retention ponds perform that job. Because of all the impenetrable surfaces in a city, all the rainfall cannot soak in during thunderstorms.
Friend's Email Address. Your Name. Your Email Address. Send Email. Back to All Blog Posts. As communities grow, the need for diverting water increases. Stormwater runoff overwhelms city sewers and can damage nearby streams and rivers through erosion. Handling the stormwater near its source can save millions in costly repairs that would otherwise be directed at correcting erosion or controlling flooding. A common method for managing stormwater is to build a basin.
Basins are meant to collect the water, and release it at a rate the prevents flooding or erosion. There are two main types of basins--detention and retention--and we will take a look at each of those today. The main difference between a detention basin or retention basin, is the presence or absence of a permanent pool of water, or pond.
The water level is controlled by a low flow orifice. In most cases, the orifice is part of a metal or concrete structure called a riser. A detention, or dry, pond has an orifice level at the bottom of the basin and does not have a permanent pool of water.
All the water runs out between storms and it usually remains dry. A retention basin or pond has a riser and orifice at a higher point and therefore retains a permanent pool of water. A retention pond looks like a regular pond, but plays an important role in controlling stormwater runoff. The basins are important for storing and slowing stormwater runoff from nearby areas, especially areas with asphalt or concrete development.
Stormwater runoff flows much faster from these surfaces than naturally occurring areas and needs to be diverted to ensure the runoff occurs at the desired rate. The amount of cleaning and treatment of the water is limited. Dry basins, or detention basins, only control flood flows. A retention pond can also provide some water quality benefits by reducing pollutants and sediments. Long ago, ancient civilizations recognized the need to develop practices to control flood waters, remove waste, and collect rain water for domestic and agricultural uses.
In the modern age, stormwater management facilities continue to be an important component of urban development to control the increase in the volume of rainwater flow and reduce pollutants in our lakes, rivers, and streams. The construction of buildings, parking lots, sidewalks, and other similar improvements decrease the available area for rainfall to infiltrate into the ground.
Additionally, due to the loss of vegetative surface cover with new developments, the rate of stormwater runoff increases significantly. If the post-development runoff was allowed to freely discharge off-site, it would run off into creeks or drains too quickly and might cause erosion or flooding. The most common structural facility constructed to slow the rate of stormwater runoff is the stormwater pond.
Stormwater ponds are essentially classified in two categories depending on their function — detention or retention. Depending on the physical constraints and conditions, they can be wet permanent pool or dry. Detention Generally, detention ponds provide only flood control measures and are known as dry ponds. Detention ponds help control the rate of flow by using a control device that maintains the pre-development rate of flow. The volume of the detention pond is calculated by comparing the pre- and post- development runoff volumes.
The difference is the detention volume. Usually, the controlled device is placed at the entrance to the outlet pipe to control the rate of flow to the pre-development rate. The pond is intended to drain the stormwater within a period of time to make the volume available for the next storm event.
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