Roads and highways play a vital role in shaping the economic prosperity of a community, as well as the quality of life for its citizens. Unfortunately, the motor vehicles that regularly utilize them are not only polluting the air, but a community’s stormwater runoff as well. The most common pollutants can include: oils and grease; heavy metals from car exhaust, worn tires and engine parts, and rust; road salts; and sediments from construction vehicles
Across the country, landscape architects are introducing ecologically-safe design elements that address stormwater runoff problems and improve water quality. Several of these strategies, which fall under the heading of “green” infrastructure, are detailed below.
Bioswales and wetland mitigation
Many landscape architects are implementing bioswales in projects. Placed within medians or parallel to a road, a bioswale captures stormwater and slowly treats it before it infiltrates the ground. Bioswales typically consist of a sloped canal featuring specially engineered soils and plants, as well as rock barriers. These materials help reduce the amount of harmful chemicals—such as phosphorous, nitrogen, and lead—often found in stormwater runoff.
In addition to mitigating the contaminants found in runoff, bioswales can help curb the peak runoff rateby adding a detention or retention pond between the runoff area and the receiving body. These ponds temporarily store stormwater runoff while containing suspended solids and other contaminants. This helps reduce the erosion impact of stormwater events.
Bioswales allow for the contaminants present in a large volume of water to be treated in a shorter time than with other stormwater management methods. Because they are often used for the drainage of large impervious areas, bioswales are typically featured in highway projects.
Also, many transportation projects are also tackling stormwater issues through wetland mitigation. Wetlands have many widely known functions, including stormwater retention and water-quality improvement. Wetland mitigation typically refers to the act of replacing the function and value of an affected wetland by creating, restoring, or enhancing a wetland in another suitable location. The process includes the consideration of groundwater, soils, plantings, and other features.
Complete streets practices
Many studies have shown that water quality becomes degraded when total impervious surface exceeds 10 percent (and in some cases, at even lower levels). This indicates that a close relationship does exist between urbanization and water quality.
Increased urbanization has become an issue for countless communities across the U.S. More hardscapes and impervious surfaces results in more rain that runs off roads and highways in excessive amounts. This stormwater often contains pollutants, meaning it can have a harmful effect upon the public and economic health of a community.