Physically Based Green Roof Model

A green roof is a multilayered vegetated roof covering consisting of a root barrier, a waterproof membrane, an under drainage system, and a layer of growing medium covered by plants. The physical principles governing the primary hydrologic and hydraulic processes in the growing medium by infiltration, drainage and recession are described. Contrary to conventional infiltration modeling approaches in which all rain water is used to advance the wetting front, the model suggests that a portion of rain water will directly drain through the growing medium to the under-drain after the field capacity is exceeded but before the growing medium is completely saturated. The model has been tested successfully using more than three years flow survey data from the green roof of Hamilton Building of Portland, Oregon.