Water Resources Research Act Program

Principal Investigators: Dr. Pradeep K. Behera

Abstract: In spite of massive public investments in sewage and drainage infrastructure, runoff volume and flooding from urban areas and pollution loading from wetweather flows (rainfall and snowmelt) continues to have significant impacts on receiving waters. Trends in urbanizations, increased quantities of urban wetweather flows and corresponding increase in pollution loadings discharged to receiving waters demand that wet-weather flow control systems be planned and engineered to effect higher levels of water quantity and quality control. Similar to many older cities in the nation, the sewer system in the District of Columbia is comprised of both combined and separate sewer systems. It has been recognized that these systems contribute significant pollution to the Anacostia and Potomac Rivers and Rock Creek through Combined Sewer Overflows (CSOs) and Storm Sewer discharges during wet-weather events [1-3]. These overflows and associated pollutant loads can adversely impact the quality of the receiving waters. The severity of the problem has been continuously emphasized due to climate change, aging drainage infrastructure and high impervious areas. The high impervious cover resulting in higher runoff volume and with faster velocities to local receiving waters through CSOs and polluted stormwater. Anacostia River was determined to be one of the most polluted water bodies in the nation mainly due to the combined stormwater and municipal wastewater discharged to it during peak runoff [4]. A cost effective and sustainable way to reduce the impacts of stormwater quantity and quality has been implementation of best management practices such as low impact developments, rain barrels, green roofs, bio-retention ponds and structural runoff control etc. However due to the high cost of land in dense urban areas such as the District of Columbia it is highly desirable to minimize the land occupied by these facilities by optimizing their performance. In last few years, District has been emphasizing not only implementation of green roofs as means of runoff quantity control but also utilization of availability of number of flat roofs. The goal of the proposed research is to evaluate runoff control performance and development of design guidelines for green roof systems for District of Columbia and mid-Atlantic climatic region. To develop green roof design guidelines, there is a need to collect runoff data from green roof systems and evaluate runoff control performance based on the soil media depth and slope of the roof. DC WRRI funded the Phase I of the project to build two green roof systems and the project included design and construction of two bench scale models with each having 50 square feet of roofs which has been placed at the central quadrangle within the Van-Ness campus of University of the District of Columbia. One roof is comprising of traditional shingles depicting the impervious surface of roofs and associated runoff generation and other roof is comprising of the green roof system depicting the conversion of impervious to pervious surface for volumetric runoff control. In the Phase II, we are planning to collect the rainfall and runoff data from the two roof systems. The roof systems will be equipped with runoff collection systems to visualize and measurement of runoff from the green roof systems. To evaluate the runoff control performance, two key parameters – soil media depth and roof angle will be considered. Runoff volume data will be collected from variable soil media depths and viable roof angles. The performance of the green roof will be assessed and will be utilized to develop preliminary design guidelines. The outcomes of this seed grant research include understanding of impact of green infrastructure such as green roof systems on the storm-water quantity and quality in the District of Columbia. The proposed mobile green roof systems will also be used for academic demonstration of stormwater runoff volume control for elementary to high school students, university students as well as public.