Importance of an efficient tide-surge interaction model for the coast of Bangladesh: a case study with the tropical cyclone Roanu

Abstract

In this study, shallow water equations (SWEs) in Cartesian coordinates were used to foresee water levels (WLs) on account of the nonlinear tide-surge interaction (TSI) associated with the recent cyclonic storm Roanu that hit the eastern coast of Bangladesh. A fully explicit finite-difference method (FDM) was implemented to solve the SWEs. A one-way nesting approach was implemented for incorporating coastal complexity with the lowest cost. The land-sea interface of every nested scheme was made favorable for employing the FDM via the stair-step technique. To incorporate river dynamics, freshwater Meghna River discharge was taken into consideration in the innermost scheme. An appropriate tidal regime in the domain was established after forcing the sea-level to be oscillatory applying the four effective tidal constituents, viz. M2 (principal lunar semidiurnal), S2 (principal solar semidiurnal), K1 (lunisolar diurnal), and O1 (principal lunar diurnal) on the southern boundary of the outermost scheme. Numerical experiments were performed by the model to estimate WLs due to tide, surge, and TSI associated with tropical storm Roanu in the coastal areas of Bangladesh. Our estimated WLs due to TSI were in good agreement with the observed data procured from the Bangladesh Inland Water Transport Authority (BIWTA) and some reported results. The model was found to perform well on the basis of the root mean square error (RMSE) values and computational cost.