Optimisation of Coupled Green Roof and Permeable Pavement for Flash Flood Mitigation

In recent years, urban pluvial floods have significantly increased, because the rain storm cannot be fully assimilated by a city’s drainage system. Climate change and rapid urbanization have contributed significantly to the increase in flood risk. To mitigate floods, low impact development (LID) technologies are sustainable drainage solutions for urban storm water management. This study aims to choose the optimal LID design through twelve scenarios consisting of permeable pavement (PP) and green roof (GR) in different proportions, which were applied in the Boudjlida district of Tlemcen province in Algeria. The optimal scenario is the one that can minimize the peak flow and the run-off volume with the lowest budget. To attain this objective, the Storm Water Management Model (SWMM) is first used to quantify the storm water run-off in sub-catchments and maximum flow in pipes. Then, the cost-effectiveness (CE) method is used to assess the economic benefit of different designs of LID practices in urban areas. The economic benefit is a criterion that balances hydrological performance and costs. This study found that out of 12 LID scenarios proposed, the scenario N° 9 which was constituted by 100% of permeable pavement and 50% of green roof was the optimal scenario. Also, for all combined scenarios, the reduction rate of run-off is between 40.68% and 17.52% and for peak flow, the reduction ranged from 62.23% to 29.52%, indicating the LID control is a powerful tool to mitigate inundations