Effects of the drainage system and impervious surfaces on urban flooding in Dhaka City

Abstract:

Dhaka city suffers urban flooding in every monsoon because of heavy rainfall, poor drainage system (both natural and human made), and excessive impervious surfaces. Although urban flooding has severe health, socio-economic, and environmental consequences on inhabitants of the city, effects of the drainage system and excessive impervious surfaces on urban flooding are poorly studied. We are conducting a study on the impact of the drainage system and impervious surfaces on urban flooding during the monsoon to provide a pathway for better urban planning. To this end, first, we estimated the area of impervious and pervious surfaces of a critical watershed in Dhaka city. Next, using an ordinary differential equation, flood levels will be simulated during monsoon. Later, the contribution of water discharged through the drainage system and pervious surfaces will be calibrated against measured flood levels. Estimation of impervious surfaces consist of ~90% of the total surface in the study area demonstrating that only ~10% of the surface is available for drainage through pervious surfaces. The calibration study will reveal volume of water discharged through the drainage system and pervious surfaces. Also, analyses will depict how the ratio between pervious to impervious surfaces impacts flooding. Furthermore, this study will provide an optimal ratio between pervious to impervious surfaces to avoid flood in the study area. This study will be extended to the whole city by including other critical variables that regulate urban flooding, such as elevation, river proximity, embankments, urbanization.