Research Highlights

Swales Research Assists Stormwater Management

A swale evaluation in progress

Podcasts

Listen to or download the podcast to learn more about how NRMRL research helps to support the protection of human health and the environment.

NRMRL water researchers are developing innovative methods to help communities reduce the damage to landscapes and streams caused by heavy rainfall runoff and the pollutants it carries. An increasingly common approach uses the swale, a shallow "engineered ditch," that provides stable routing for stormwater flows while mitigating the runoff-carried pollutants. Researchers at NRMRL's Edison, New Jersey, facility are testing the performance of swales under various conditions to document the capabilities and test the limits of this technology.

About Swales

Swales provide a green, low-cost drainage option for highways, farms, industrial, commercial, and residential areas. Under the controlled conditions possible at the Edison outdoor laboratory, researchers can alter the swale dimensions, shape, and runoff volume and timing to collect performance information without the risk to personnel and equipment of actual roadside testing during a rain event. Controlled experiments also compensate for uncertainty of weather, access, and other logistical issues that make field testing risky and costly. The control provided by the unique facility allows researchers to approach runoff replication, an impossibility in the field.

Each of the three swales in the test project is about 130 feet long with slopes ranging from 5 percent to 0.5 percent, with 1 percent as the generally accepted preference. The subsurface of each swale is divided into four separate watertight longitudinal segments enabling researchers to collect data supporting computer model development that predict infiltration rates and chemical reactions. Swale subsurface is constructed in vertical layers beginning with an impermeable bottom liner. The liner is covered by an 8-inch layer of gravel, a 1-foot replaceable media layer, and an uppermost vegetation layer. The vegetation creates a rough surface that slows the water flow and allows particles to settle. The swales promote flow into the layers below, reducing the total volume discharged.

Mixed supply and collection tanks, along with pipes in the gravel layer, allow researchers to collect samples of infiltrating water for chemical analysis performed at an onsite laboratory. Electronic monitors record the flow and depth of surface water. Buried sensors measure soil moisture and temperature of the media layer. Water within the gravel layer is monitored for dissolved oxygen, temperature, pH, turbidity, conductivity and oxidation-reduction potential. Flow meters record the rates and volumes pumped to the swales, infiltrated, and discharged.

All water used in the experimental program is stormwater runoff routed from an onsite storm sewer outfall to collection tanks. During an experiment, the stormwater is mixed and then pumped to the top of the swales. Overall, the one-acre NRMRL swales research is addressing the questions of how best to design, install, and maintain swales to achieve the largest pollutant reduction at the lowest cost while meeting a community’s total drainage needs.

The Larger Picture

Based on perceived benefits, some communities are requiring developers to incorporate swales into new residential construction as a less-costly and more eco-friendly alternative to conventional curbs and gutters for managing stormwater runoff. EPA also recognizes swales as part of a low-impact development strategy that helps to reduce a community’s environmental footprint on the landscape.

The swales program is part of a larger array of long-term projects at the 20-acre Urban Watershed Research Facility that also evaluates constructed wetlands, detention and retention ponds, rain gardens, and porous pavement projects. The goal is to help watershed managers reduce pollutants to receiving streams and lakes, thus ensuring a continuing supply of high-quality drinking water and helping to meet the “fishable and swimmable” water quality goals called for by Congress in the Clean Water Act.

Contact

Cindy Kirchmer, Office of Public Affairs (513) 569-7737