The Effect of Modifying the Existing Green Spaces Compared to Other Methods of Urban Flood Management in Reducing the Volume of Runoff (Case Study: Chahar-Cheshme River Basin, Mashhad)

Flood is one of the natural events that in recent decades, due to the expansion of urbanization and land use changes, causes many financial and human losses in different regions of the world, annually. Therefore, flood management in cities by low-impact development methods has become crucial. The current research compares the performance of the approaches of rain gardens, storage units, and bio-retention cells to directing surface runoff to green spaces using the SWMM model for the Chahar-Cheshme River basin of Mashhad city. Due to the lack of a hydrometric station in the city, precipitation and peak flow in the channel were measured for 20 rainfall events from April 2023 to May 2024. The evaluation index including RMSE, NS, and KGE shows the appropriate performance of the model for peak flow estimation. The sensitivity analysis of the model showed that impervious area, width, and impervious area’s roughness coefficient are the most effective parameters to the peak flood discharge, respectively. In terms of reducing the peak discharge and volume of the flood, bio-retention cells, runoff directing to green space, and rain gardens had the best performance, respectively. However, the bio-retention cells had the best performance, but considering operational and maintenance costs, and other conditions, modifying green spaces to direct surface runoff to these spaces is a better and more logical choice for flood management in the study area.