What is a Detention Tank?

Article by: Brentwood, July 19, 2022
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According to the American Society of Civil Engineers’ Report Card for America’s Infrastructure, stormwater runoff causes 9 billion dollars in damage every year. Stormwater runoff is defined as water generated from rain or snow that flows over land or impervious surfaces (like paved roads and rooftops) and is prohibited from naturally absorbing into the ground. Constant land development is leading to more impervious surfaces being developed which, in turn, leaves less natural soil available for stormwater to soak into. This results in higher runoff rates, increased flooding, and increases the likelihood of stormwater collecting harmful pollutants along its journey to our waterways.

To combat this excess and protect our environment, many local regulators require some sort of stormwater detention system to be implemented. Stormwater infrastructure comes in many forms, but the primary one we’ll focus on in this article is a detention tank. Let’s take a closer look into what detention tanks are, how they operate, and a few different types of systems commonly used for detention applications.

Defining Detention Tanks

Detention tanks are artificial structures designed to temporarily hold stormwater runoff. Stormwater runoff enters these basins via storm drains. Runoff is collected until peak inflow volumes subside. From there, the  detained stormwater is discharged at a controlled rate into nearby waterbodies. This method of stormwater management helps to reduce flooding in our communities and protects coastal areas from erosion.

You may hear the terms detention tank and retention tank used interchangeably when referring to stormwater management systems, but these are two separate systems that serve different functions. While both operate on the same general principle of managing stormwater volume to control flooding and erosion, the main difference comes from their storage methods. Detention tanks gradually discharge runoff until the basin is completely drained. Retention tanks, on the other hand, permanently store water. Stormwater collected in retention tanks will later be recycled for purposes like irrigating gardens or flushing toilets.

Common Types of Detention Tanks for Stormwater Control

Sketch of how a detention tank works in a parking lotDetention systems can be installed either above ground or below ground. Traditional above ground detention systems usually entail an excavated pit that resembles a pond as it collects stormwater. While above ground systems have proven to be an effective management solution for many years, underground detention systems are better suited to maximize the amount of developable land available for construction projects. Because of this flexibility, underground detention systems are an ideal solution for applications dealing with tight spatial constraints. Most subsurface detention systems are installed beneath parking lots, lawns, athletic fields, and other hardscape surfaces.

Brentwood offers the Module 25 series as a solution for stormwater retention, detention, infiltration, and rainwater harvesting applications.

There are two main product types currently on the market for underground detention systems: box and arch-shaped products. Both are designed to achieve the same goal of creating a void space for stormwater and supporting the surface above. However, the best type of detention system to use ultimately depends on your site-specific project. We compare both products in terms of overall footprint, capacity, buoyancy, ease of installation, and strength in our blog: Stormwater Management: Five Reasons to Use a StormTank Module Over an Arch Product.

The Bottom Line on Detention Tanks

There is no way to control the weather, and we aren’t going to have the ability for perfect grading and runoff control year-round. However, the advanced flexibility that underground detention tanks offer today provides seamless and discrete stormwater runoff control to help keep our communities as safe and clean as possible.

If you are looking for a stormwater management solution for a detention application, our industry experts are happy to discuss your site-specific needs. Use our Find A Pro search tool to locate a StormTank expert in your area who can provide professional engineering and contractor guidance for your next commercial, residential, or recreational project.

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