Modeling Hydrologic Performance of a Green Roof System with HYDRUS-2D

A green roof is an environmentally friendly best management practice for volume reduction, peak flow reduction, and peak delay of stormwater runoff from impervious rooftops. In this study, HYDRUS-2D was used to model the hydrologic response of a pilot green roof system. The root-mean-square deviation (RMSD) of growth media volumetric water content values between model and field measurements ranged between 0.38 and 1.74%. A method was developed to use the water content profile at three media depths to derive regression equations that predict hydrologic performance. These equations show that runoff volume reduction follows an inverse relationship between media field capacity and precipitation depth, that peak flow reduction obeys a second-order equation between media field capacity and precipitation depth, and that peak delay time can be approximated by a third-order equation that includes maximum capacity and precipitation depth. The R(2)s values of the regressions range between 0.87 and 0.99. These derived equations can be used for performance evaluations or design work, including determining the necessary green roof media depth to meet Leadership in Energy and Environmental Design (LEED) runoff reduction requirements. (C) 2015 American Society of Civil Engineers.