Spatio-Temporal Variability of Tidal Velocities in the Rivers of the Indian Sundarban Delta: A Hydrodynamic Modelling Approach

This study investigates the spatio-temporal variability of tidal velocities in the Sundarban River System. The industry standard numerical tool MIKE 21 Flow Model was applied to simulate tidal velocities in the river system. Bathymetry data from GEBCO ( https://www.gebco.net/ ) and surveyed bathymetry were used in model construction. The tidal velocities were measured using Acoustic Doppler Current Profiler at two tidal channels, namely Chaltabani Khal in the south and Durgaduani Creek in the north. The simulated tidal velocities were compared with the observed tidal velocities at two different locations at two different times to calibrate and validate the model. The validated model identified 11 high-velocity sites within the Sundarbans, where flow velocity of up to 2.46 m/s was observed for the study period. The highest tidal velocity along with the higher tidal ranges was found during the March equinox (March/April), whereas the lowest velocity along with the lower tidal ranges was observed during the summer solstice (July/August). The results showed that the velocities within the narrow channels were stronger compared to those in the wider channels. The simulations revealed that about 53% of tidal velocities were more than 1 m/s throughout a day in a particular site on the Bidyadhari River. A variation of tidal velocities from 0.5 to 1.0 m/s was also observed for other areas for a higher period during a day. This study also found that the shorter flood tide period caused stronger flood tidal velocity than the ebb-tidal velocity. Seven possible deployment locations for harnessing tidal energy in the Sundarbans delta were identified by the model in this study. It is expected that the study, the first of its kind in this region, will be useful in developing and planning for coastal resilience and sustainable development in a delta vulnerable to climate change and sea-level rise.