Numerical investigation of surge–tide interactions in the Bay of Bengal along the Bangladesh coast

The tidal amplitude at the Bay of Bengal along the Bangladesh coast varies from 2 to 7 m, whereas the tidal phase differs by more than 3 h from the outer part toward the inner part of the Meghna Estuary. At the time of cyclone landfall, the tidal phase has a significant impact on surge height, arrival time and duration. In this paper, the nature of surge–tide interactions at the Bay of Bengal along the Bangladesh coast has been investigated using a two-dimensional nonlinear shallow water model coupled with a storm surge model. Two previous major storm surge events along the Bangladesh coast have been analyzed for surge–tide interaction: Cyclone 1991 and Cyclone Sidr in 2007. To investigate the impact of the tidal phase on surge characteristics, in addition to the base cases, storm surges have been calculated at different phases of an entire tidal cycle at 1-h intervals. The results indicate that during the ebb tides the calculated total surge height of the surge–tide interaction model was higher compared to the total surge height obtained by superimposing surge height that is separately calculated with mean water level over the local tidal water level; the opposite occurs during high tide. The surge propagation time toward the inner part of the bay significantly varied depending on the tidal phases. When the tidal water level along the coast was low, the speed of surge propagation was much slower compared with when the tidal water level was high. The surge duration increases when the falling surge profile encounters an opposing strong tidal current at the landfall location.