Urban flooding is a significant challenge that has become more frequent globally in the last two decades. It occurs when rainwater reaches an urban area more quickly than it can be transported to a water body, such as a river or lake, due to a prolonged absorption rate to the soil. In urban areas like Chennai, which have a greater degree of impervious regions and disconnected flood pathways, flood waters struggle to follow the natural flow path of the bare terrain. An efficient drainage system is key to draining artificially induced flooding. This study assesses the performance of the existing stormwater drainage system in a residential zone of Chennai between the Adyar and Cooum Rivers. The assessment employs the MIKE+ model to evaluate the performance of the stormwater networks. This model calculates runoff from the watershed using the hydrological component. Subsequently, the computed runoff is fed as input into the 1D stormwater model. The 1D stormwater model is coupled with the 2D hydrodynamic routing model to manage junction overflows onto the urbanized floodplains and overland flows from the floodplains into the junctions. The developed model setup is validated for the 2021 Chennai flooding event. The validated model setup is further used to evaluate the effectiveness of the existing integrated stormwater drains (ISWD) under different rainfall durations. This comprehensive investigation not only aids in understanding the effectiveness of the ISWD but also informs the decision regarding resizing or extending the existing ISWD. Ultimately, this contributes to improved flood preparedness in the city.