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Grass Swales for Pollutant Removal |
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This project began in 2002 and is now complete. It was funded by the Maryland State Highway Administration. Grassed swales have been used near roadways for many years for the conveyance of storm water runoff. Water quality enhancements can be realized in these swales through sedimentation (due to the lower velocity induced by the vegetation), filtering by the grass blades, infiltration, and likely some biological processes. Nonetheless, good performance data and mechanistic understanding of swale design parameters are not available.
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The research system was designed as an input/output comparison study to determine the removal of water quality parameters most important for roadways (total suspended solids, total phosphorus, nitrate, nitrite, total Kjeldahl nitrogen, cadmium, lead, copper, and zinc). Two grass swales were constructed in the median of Maryland Route 32 near Savage, Maryland to allow the determination of discharge water flow and quality parameters. One swale receives runoff directly from the highway, while the other has the shallow sloped filter strip pretreatment area between it and the highway. Because any direct monitoring of input parameters would be intrusive and affect output, an indirect method was used. A concrete channel, with similar dimensions and a roadway drainage area identical to those used for the grass swales, was constructed immediately adjacent to the roadway. The water flow and quality in this channel is assumed to be identical to the input for the swales. Flow data and water samples for all three channels were being taken over 6-8 hour sampling periods at regular intervals during a rainfall event. | ||
| Results indicate excellent removal of suspended solids and heavy
metals. Flow peaks and volumes are also reduced by the swales.
A manuscript describing performance results and conclusions is in preparation.
This work was being completed by Master's student Jim Stagge. |
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September 26, 2006