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