Performance Evaluation of Stormwater Drainage System Subjected to Multiple Flood Drivers

Urbanization is a vital catalyst for socio-economic development in developing countries, such as India. However, rapid and poorly planned urban expansion has resulted in increased vulnerability to flooding during heavy rainfall. Stormwater drainage (SWD) systems emerge as cost-effective solutions to mitigate these challenges. Many major Indian cities, including Chennai, are situated in coastal and riverbank areas. During intense rainfall in upstream catchments, rivers carry significant water to the coastal areas of the city, challenging SWD systems to efficiently discharge water at outlet points. Complicating matters, the occurrence of surges from cyclonic effects in the sea further impedes river water transport. Consequently, urban areas experience prolonged flooding due to the compound effects of multiple drivers. This study evaluates the performance of the SWD system subjected to multiple flood drivers in the coastal part of Chennai city using the freely downloadable HEC-RAS model. The assessment encompasses pluvial, fluvial, and storm surge-induced flooding scenarios. The hydrological component of the model computes runoff from the watershed, which is then input into a one-dimensional (1D) stormwater model. To address compound flooding, the 1D model is coupled with a two-dimensional (2D) hydraulic routing model, enabling the management of junction overflows onto urbanized floodplains and simulating overland flows from floodplains into junctions. The comprehensive investigation not only enhances our understanding of the effectiveness of SWD during flooding but also provides valuable insights for decision makers. The study informs decisions related to resizing or expanding the proposed SWD infrastructure, ultimately contributing to improved flood preparedness and resilience in the urban landscape.