Modeling stormwater runoff from green roofs with HYDRUS-1D

A study was conducted on the effectiveness of green roofs to mitigate stormwater using computer simulation. In this study, the stormwater performance was simulated for a modular block green roof using a packaged soil moisture simulation, HYDRUS-1D, with simulation results verified by study site data. Simulations were run using HYDRUS-1D for 24-h design storms to determine peak flow, retention and detention time for runoff. Storm data collected as part of a green roof study in Athens, Georgia, USA were used to validate HYDRUS-simulated runoff. The study site consisted of a 37 m2 (400 ft2) modular block green roof containing engineered soil and vegetation including several Sedum species. The study revealed that rainfall depth per storm strongly influences the performance of green roofs for stormwater mitigation, providing complete retention of small storms (<2.54 cm) and detention for larger storms, assuming the measured average moisture content (∼10%) as the antecedent condition.