Erosion-accretion pattern in the tidal-rivers of Indian Sundarban in relation to estuarine hydrodynamics

Mapping the changes in the deltaic-coastal zone under changing hydrodynamic conditions is crucial for developing a concise picture of coastal vulnerability. The present study provides a comprehensive idea of changing scenario of rivers in the world's largest delta-Sundarban, using a variety of remotely sensed data and measurements, and relating these changes to hydrodynamic conditions. Bathymetric changes have also been estimated using Landsat imageries, calibrated with bathymetric chart data. We document a substantial dynamic variation between western and eastern sections of the Sundarban tidal rivers, as well as between the northern and southern parts. As such, banks adjoining the Saptamukhi and Thakuran rivers in the west have accreted by +43.48 ​km2 and +6.13 ​km2 respectively, while the net change in the eastern rivers like Matla, Gosaba, and Hariabhanga river systems shows a loss of −51.54 km2, –13.92 km2, and –13.82 km2, respectively, over the last century. Erosion rates have decreased from the southern seafront zone to the northern interior parts due to the low wave exposure, and high tidal range. The accretion rate has increased on the same ground. The depth of these rivers has also changed significantly. For instance, the depth of most sections along the Thakuran river has increased from 5 to 7 m to about 7–10 m during the period 1987–2016. The findings of this study will help researchers all around the world in understanding the centurial dynamics of tidal rivers, and by comparing these to other deltas, it will be possible to emphasize the relative vulnerability of major deltas to current sea level rise.