Evaluating the Hydrologic and Water Quality Benefits Associated with Retrofitting Vegetated Swales with Check Dams

The North Carolina Department of Transportation (NCDOT) is required by the National Pollutant Discharge Elimination System (NPDES) stormwater program to mitigate stormwater runoff from its facilities. Therefore, the NCDOT highway stormwater program implements retrofits across the state. Due to recent passage of the Jordan and Falls Lake rules, the Department needs additional technologies that may be applied to treat stormwater. Swales have been used to convey water away from the roadways since the Roman Empire, and remain the most common and simplest treatment tool at Department of Transportation's (DOT's) disposal. However, little research has focused on their ability to be used as a water quality treatment stormwater control measure (SCM). Past research on dry swales in North Carolina has shown moderate (23%) volume reduction and excellent reduction of sediment bound pollutants (Petre et al. 2013). However, amendments to existing swales could improve performance, leading to greater treatment credit for these SCMs. This research project is actually two sets of studies that may improve swale performance: (1) check dams and (2) bioswales. Check dams, structures placed perpendicular to flow to retain water in a swale, are a simple retrofit that could be used in existing roadside swales across North Carolina. Little previous research or design specifications are available, and therefore research is justified to quantify their water quality and hydrologic benefits. Check dams decrease flow velocity, and thus should provide greater treatment for sediment-bound pollutants. Additionally, bioswales - which have specialized media designed to treat certain pollutants - are seeing more use. Soil media targeted to remove heavy metals, bacteria, and phosphorus capture are being considered elsewhere. Two previously monitored dry swales (Luell 2011; Winston et al. 2012) will be retrofitted with check dams. At one site, the check dams will contain a phosphorus sorbtive media, while the other will have standard-design check dams. This will provide NCDOT with data on dissolved phosphorus removal using check dams, important for the Jordan and Falls Lake watersheds. Hydrologic retention (peak flow reduction, volumetric reduction) as well as nutrient, sediment, and heavy metals removal will also be measured. A third bioswale site - targeted for the removal of bacteria - will be monitored in Brunswick County. Eighteen paired grab samples will be taken to determine the removal efficiency of the bioswale. The North Carolina State University Department of Biological and Agricultural Engineering (NCSU-BAE) will cooperate with Coastal Carolina University on this aspect of the project. Flow monitoring may also be attempted at the site. Monitoring of these practices will begin in October 2013 and will be completed by April 2015. Conclusions from the study will include design recommendations for check dams, the performance of check dams for improvement of loading of nutrients, sediment, and heavy metals, and the performance of a bioswale for bacterial removal. These data have the potential to improve swale design (the most commonly used SCM for NCDOT) across the state, and NCSU will facilitate interaction with The North Carolina Department of Environmental and Natural Resources (NCDENR) to adjust how swales with these simple retrofits are awarded pollutant removal


  • English


  • Status: Completed
  • Funding: $197547.00
  • Contract Numbers:


  • Sponsor Organizations:

    North Carolina Department of Transportation

    Research and Development
    1549 Mail Service Center
    Raleigh, NC  United States  27699-1549
  • Project Managers:

    Kirby, John

  • Performing Organizations:

    North Carolina State University, Raleigh

    Department of Biological and Agricultural Engineering
    Box 7625
    Raleigh, NC  United States  27695
  • Principal Investigators:

    Hunt, William

  • Start Date: 20130816
  • Expected Completion Date: 0
  • Actual Completion Date: 20150816
  • Source Data: RiP Project 35252

Subject/Index Terms

Filing Info

  • Accession Number: 01492621
  • Record Type: Research project
  • Source Agency: North Carolina Department of Transportation
  • Contract Numbers: FHWA/NC/2014-17
  • Files: RIP, STATEDOT
  • Created Date: Sep 11 2013 1:01AM