Roadside Guide to Clean Water: Stormwater Basins
Stormwater Basins at a Glance
Stormwater basins are the commonly seen, though perhaps unnoticed, impoundments that are built near developments (residential, commercial, and others) to temporarily hold stormwater during rain and snowmelt events. These basins are meant to prevent high volumes of water from rushing into nearby streams during storms. After the rain event, the stored water is released slowly, into either a nearby stream or the soils and groundwater. Some stormwater basins hold water at all times, like ponds, while others that drain completely look simply like bowl-shaped areas planted in grass.
How Stormwater Basins Work
During a storm, rainwater is collected from streets and parking lots and directed into the basin. The stormwater is stored temporarily and then released slowly in order to prevent flooding and erosion. Stormwater basins improve water quality in different ways depending on how they were designed. Dry basins slowly release stormwater directly to a stream through a controlled outlet pipe. Infiltration basins have porous soils so that water can soak in and become groundwater. In both cases, these types of basins are meant to dry out between storms. There are also retention basins, or wet ponds, that are designed to hold some water at all times and look like typical ponds. For the most part, basins are meant to reduce the volume of water entering a stream during a storm. Infiltration and retention basins may also remove some stormwater pollutants. More recently, bioinfiltration basins have become popular. These basins use plants to help filter the water before it is returned to the environment.
Community Benefits of Stormwater Basins
- Stormwater: Reduces stormwater runoff
- Groundwater: Recharges groundwater
- Climate Change: Promotes climate change resiliency
- Flooding: Mitigates flooding
- Pollution: Reduces pollution
- Savings: Provides cost savings
You can expect to find stormwater basins in urban, suburban, and rural settings.
How to Recognize Stormwater Basins
Infiltration basins have no outlet but instead drain slowly into the soil, which provides some water quality improvement. Photo by Jennifer Fetter.
Dry basins slowly release water through an outlet pipe. The basin also has an emergency overflow drain at the top of the concrete riser. Photo by Kristen Kyler
Wet ponds can provide some water quality benefits by allowing sediment to settle out before stormwater is released. Photo by Jennifer Fetter
Many dry basins are planted with turfgrass and look like large, depressed lawns. The concrete inlets and outlets are often the only sign that it is a basin. Photo by Jennifer Fetter
Some basins are planted and maintained as natural areas. They may be bioinfiltration basins.
This basin is about to get replanted with native flowers instead of turfgrass to help improve its ability to filter pollutants from stormwater. Photo by Andy Yencha
