Water Resources Research Act Program

Details for Project ID 2015DC170B

Evaluation of green roof effectiveness for nitrogen, phosphorus and suspended solid reduction in runoff from precipitation events

Institute: District of Columbia
Year Established: 2015 Start Date: 2015-03-01 End Date: 2016-02-28
Total Federal Funds: $9,993 Total Non-Federal Funds: $24,604

Principal Investigators: Stephen MacAvoy

Project Summary: One of the challenges urban areas (including Washington DC) face is high storm water flow from resulting from impermeable surfaces. This often results in increased sedimentation, flooding, pollutant flux and combined sewage/storm water discharge to DC rivers. Green roofs are now being considered to reduce the storm flow from buildings, and the Washington DC government is even granting stormwater tax credits to businesses that incorporate water retention practices. An added benefit for having the roofs (in addition to water retention) may be the reduction of suspended solids and nutrients such as nitrogen (N) and phosphorus (P). The roofs support plants and bacteria that may retain excess nutrients and solids that would otherwise end up quickly traveling to waterways. In this proposal, the effectiveness of green roofs for limiting N, P, dissolved organic carbon (DOC) and suspended solid pollution will be evaluated. American University installed traditional green roofs (soil based) and Aqualok roofs (foam based) several years ago. These green roof types will be monitored for nutrient retention (or release) and compared to regular roofs. Collections will be made for at least six precipitation events. Based on rain volume, area of green roof, and concentration of pollutant, a "pollution absorption footprint" will be developed. The research will also allow a comparison of the two types of green roof, which differ in material weight, cost of installation, and cost of maintenance. The study will yield valuable insight into how effective green roofs are for improving our area's water quality.