A North Carolina Field Study to Evaluate Greenroof Runoff Quantity, Runoff Quality, and Plant Growth

Recent federal and state regulations require storm water runoff to be treated by structural controls in ultra-urban development. Several practices have been used in North Carolina; however, a less common storm water management practice is the greenroof. Two extensive greenroofs have been constructed within the Neuse River Basin of North Carolina. Each greenroof retained approximately 60% of the total recorded rainfall during a nine-month observation period. The average peak flow reduction for both greenroofs was approximately 85%. Water quality data indicated higher concentrations of TN and TP were present in the greenroof runoff than in the control roof runoff and in the rainfall at each greenroof site. This may be a result of N and P leaching from the soil media; the soil media is composed of 15% compost. Preliminary results from a soil column test of three different greenroof soil medias indicate that leaching can be reduced with less organic matter present in the soil media. Vegetation growth observed after the first year showed growth was significantly higher (α < 0.05) in 100 mm (4 in.) deep soil media than in 50 mm (2 in.) deep soil media.