Using Preferential Flow to Model Green Roofs

Over the past 10 years green roof has been considered an effective stormwater management tool to mitigate storm runoff in urban environment. However, the hydrologic and hydraulic processes of the green roof have not been adequately modeled. Existing approaches range from relatively simplistic infiltration models to more complex subsurface and groundwater flow models. None of these models consider the preferential or nonequilibrium flow in the layers of green roof. In this paper we present a green roof model developed based on preferential flow that accounts for the water movement between the matrix and fractures in the growth medium. The model is calibrated and validated using three years of monitoring data from multiple roofs in Seattle, Washington. The simulation results of the peak flow and total volume matched well with the observations.