A Deterministic Lumped Dynamic Green Roof Model

A green roof is a multi-layered vegetated roof covering consisting of a root barrier, waterproof membrane, under drainage system, soil, and plants. The hydrologic and hydraulic processes involved are rainfall evapotranspiration, runoff generation, detention, infiltration, and routing. To assess the effectiveness of green roof on mitigating urban stormwater runoff, a Deterministic Lumped Dynamic Model (DLDM) has been developed to simulate these aforesaid processes. This model uses the Green-Ampt equation modified by Mein & Larson (1973) and the infiltration modeling procedure described in Chow et al. (1988) as the basis. However, it further modifies them to describe how infiltration rate changes as the roof substrate wets and dries and their relationship to the Specific Retention of the roof substrate. The runoff module of Storm Water Management Model (SWMM RUNOFF) is adopted by this model for modeling the routing of infiltration through the under drainage system of the green roof. Flow survey data of 5 minutes interval from Hamilton Building in the City of Portland from Year 2001 to 2003 have been used to test the model. We have founded that the simulation results of the peak flow and total volume are matching observation within reasonable range.