What is a detention basin?

Fall is rolling in and even in sunny San Diego, rain falls are about to happen throughout fall, winter and all the way until the spring time. Every year parking lots are getting flooded and playgrounds, sport fields etc are standing under water. The question is: Is this something that could be prevented?

The answer is YES! Detention basin or ponds are created to hold and distribute rain water runoff, which prevents flooding and erosion. The area is designed to slope down into a basin/pond that will hold the water after heavy rainfalls and stores it until it slowly dries out after rain. Those basins are large excavated areas that remain empty until a rainstorm is happening.

Let’s take a closer look at how these detention basins work but before that we need to make sure to understand the difference between detention and retention ponds (only one single letter can make a big difference here):

Detention ponds provide only flood control measures and are known as dry ponds. Detention ponds helo rate of flow by using a control device that maintains the pre-development rate of flow. A device that is placed at the entrance to the outlet pipe to control the rate of flow. The pond is intended to drain the stormwater within a period of time to make the volume available for the next storm event.

DETENTION POND

Retention ponds hold a permanent pool of water and are referred to as wet ponds. The pond stays “wet” because the bottom of the pond is excavated below the water table elevation to establish a permanent pool. The pond outlet is placed exactly where you want the water to be drained.

RETENTION POND

Detention basins are created to allow for a large amount of stormwater inflow to be captured and stored while allowing for a small amount of outflow to be released at any given time. The detention pond fills up and stores water temporarily. Runoff enters the basins by flowing in from the surrounding land or from a created channel or redirected pipe. Water is usually released from the basin by gravity, through an outfall channel or pipe. As the water in the receiving channel drops, more water is able to leave the detention basin, until it is emptied or restored to its designed pool level. The basin fills and empties based on the size of the outlets/ pipes. There are ways to calculate the volume of an areas water flow.