Coastal flooding is a natural disaster that has often contributed significant causalities and loss to low-lying areas worldwide. It takes place either due to river flow from inland regions or storm surges caused by tropical cyclones. The simultaneous occurrence of extreme river flow and storm surge exacerbate the flood risk compared to their occurrence at different times. Therefore, it is essential to understand the combined effect of river overflow during a storm surge. The combination of hydrodynamic and hydraulic models is used to simulate the flood risk due to fluvial flooding and storm surge. In most of the existing studies, the models are combined in a decoupled way using freely available 2D numerical models or simple 1D-2D research codes. This approach is computationally efficient compared to a tightly coupled approach but there are avenues for critical improvements. Although the decoupled approach is computationally efferent, the hydraulic model used in river-bay framework is still computationally expensive and very little attention has been given to the choice of the hydraulic model. So far, the comparison of decoupled and tightly coupled river-bay modelling approaches and models has not been made in the existing studies. Further, suitability of the decoupled approach to analyze the non-linear interaction of river flow and storm surge has not been addressed. Along the east coast of India, there is no high-resolution study of city flooding during a storm surge. Therefore, this research focuses on developing an efficient unstructured grid-based two-dimensional river-bay tightly coupled model for simulating surge and inundation simultaneously. The bay-part of the surge simulation model is developed using an efficient flux and bed slope computation schemes and using a simple Holland-based wind model. In the inundation part of the river-bay model, two types of efficient inundation models such as fully dynamic and local-inertial equation-based two-dimensional models are developed. The performance of the models is analysed in terms of accuracy, numerical stability, and computational efficiency. It has to be emphasized that the developed river-bay model is an indigenous model for storm surge prediction and river flooding using the efficient and accurate numerical schemes.The developed model is applied to carry out a high-resolution study of city flooding during a storm surge. Further, it can be used to forecast storm surge and inundation extent in a real-time mode using the forecasted cyclone tracks and observed/simulated inflow hydrographs. Hindcasting studies can also be carried out using the developed modelto generate inundation maps for different return period wind speeds and hydrographs and for the identification of high wind speed regions along the east coast. The developed river-bay model is applied to Adyar-river basin, a part of the Chennai basin, in a coupled and decoupled modes. First, the river-bay model is validated for surge using the recent Vardah cyclone (2016) and for inundation using Chennai 2015 flood event. The high-resolution inundation simulations are carried out at finer scale ( 4m) using the Lidar based digital elevation data for various return periods of cyclone tracks and upstream inflow hydrographs. It is found from the simulations that the decoupled approach is computationally efficient. However, the decoupled approach fails to produce the surge effect on inundations for 2005 and 2015 like flood events, irrespective of the return period wind speeds. For