A shallow water model for computing water level due to tide and surge along the coast of Bangladesh using nested numerical schemes

•Investigation of tide generating forces for the purpose of increasing accuracy in water levels.•Offshore islands of the whole coastal belt along with coastal bending were incorporated.•Nested numerical schemes were exercised to save computer memory space.•Appropriate tidal regime over the model domain was generated by forcing the sea level to be oscillatory with the constituent M2.•Impacts of tide generating forces, offshore islands, river discharge and grid resolution on water levels were tested and water levels were found to be influenced by them.

A vertically integrated shallow water model is developed for computing water levels due to the nonlinear interaction of tide and surge associated with some storms that hit the coast of Bangladesh. Emphasis is given on the investigation of tide generating forces for the purpose of increasing accuracy in water levels due to a storm. Offshore islands of the whole coastal belt along with the complex land-sea interface is modeled via stair step because of the application of a rectangular grid. Nested numerical schemes are exercised in this study to save computational cost. Appropriate tidal regime over the model domain is generated by forcing the sea level to be oscillatory with the constituent M2 along the southern open boundary of the parent model omitting wind stress and tide generating forces. The previously generated tidal regime is introduced as the initial state of the sea for the nonlinear interaction of tide and surge. The model is applied to estimate water levels at different coastal and island locations of Bangladesh associated with the two recent storms AILA and SIDR that hit the coast of Bangladesh. The results simulated by the model are found to be satisfactory with observed data and reported results obtained through various investigations.