An investigation on the effect of offshore islands along the coastal belt of Bangladesh during a storm period

---------------------------------------------------------------------***-------------------------------------------------------------------Abstract In this study, a vertically integrated shallow water model is designed to estimate the water level due to nonlinear interaction of tide and surge associated with tropical storms along the coastal belt of Bangladesh. To develop the model, a fine mesh scheme, capable of covering all major islands, has been nested into a coarse mesh scheme covering up to 15N latitude in the Bay of Bengal. To incorporate accurately thickly populated small and big islands along with highly bending of the coastline along the Meghna estuarine region in the numerical scheme, a very fine mesh scheme for the region is again nested into the fine mesh scheme. Along the northeast corner of the very fine mesh scheme, the fresh water discharge through Meghna river is taken into account. The boundaries of the coast as well as of islands are approximated through proper stair step representation and the model equations are solved by semiimplicit finite difference technique using a staggered grid. The model is then applied to simulate the water levels due to the non-linear interaction of tide and surge associated with the storms SIDR and AILA. The model simulation was quite satisfactory, and then the influence of the offshore islands on the water level along the coast of Bangladesh was tested.