Investigating the hydrological performance of green roofs using storm water management model

Abstract

The green roof, also known as vegetated roof covers, or eco-roofs or natural roofs, is one of the recently developed low impact development (LID) techniques, which significantly increases water retention and thus helps to mitigate the urban flooding. In the present study, the installation of green roofs is assumed as a hypothetic retrofitting scenario according to a sustainable storm water mitigation strategy for a selected urban catchment and performance has been evaluated using Storm Water Management Model (SWMM). The model has been calibrated for the measured flow data of eight events using Nash-Sutcliffe Efficiency (NSE) Coefficient. The lowest and highest value of NSE was found 0.67 and 0.93 respectively. The hydrologic performance of the green roof was conducted under event-based as well as continuous simulation. Based on simulation results, peak flow has been reduced from 7.13 ltr/sec to 6.36 ltr/sec for Green Roof – 1 (GR-1) and 1.45 ltr/sec to 1.30 ltr/sec for Green Roof – 2 (GR-2). The simulation results point out that the integration of green roof LID contributes to the reduction of the quantity of storm water runoff by increasing the retention period. However, the hydrological behavior of a green roof is site-specific, and therefore the site-specific conditions and parameters like characteristics of the vegetation, physical properties of its layers, etc. have to be considered in the evaluation of its performance. Further, the research at the micro-level is necessary to evaluate the role of the green roof slope, the effect of vegetation cover, and the antecedent period on the performance of the green roofs for more reliable results.