Shoreline Change and Associated Beach Ridge Chenier Formations in the Subarnarekha Delta Region, India

Abstract

The chenier mechanism of the Subarnarekha deltaplain is dominated by the relative stillstand, transgression, and regression phases of marine environments in the Bay of Bengal region. The river carries sediment outlets into the shallow sea region of the Subarnarekha estuary mouth, which is further redistributed along the shoreline by the different reworking agents like waves, tides, currents, longshore drifts, and storm surges. Depending on the shoreline configurations and relative sea level positions during the stillstand, transgression, and regression phases, the voluminous sediments have been deposited around the respective shoreline positions as windblown sand sheets followed by beach ridge deposits by energetic wave actions. The inconsistency in shape, size, and orientation of the palaeo and recent sand dunes indicates the nature and strength of the sediment outlet by the Subarnarekha estuary associated with the strengthening monsoon phases, the dominance of southwestern and northeastern monsoons, and relative sea level positions in the deltaic region. The topographic expressions and width of inter-dune swales illustrate the relative strength of regression phases in the different periods. The present study has been carried out along the ~90 km coastline on both sides of the Subarnarekha delta region, from the Rasulpur river in the east to the Budhabalanga river in the west. The nine stages of dune ridges have been identified and demarcated using satellite imagery and field observations. The highly elevated and widely extended Contai-Paniparul dune ridge is situated at the extreme landward extent of the beach ridge–chenier system on the left side of the delta, while the Baliapal dune ridge is situated analogous to it on the right side of the delta. Such an extent is identical with the steady stillstand phase around 7000 years before present. The narrow and small extent of the Talsari dune ridge in the recent shoreline position demonstrates the negligible period of the stillstand phase (around 50 years), but shows dynamic shoreline characteristics during the monsoon months followed by the recent trend in sea level rise.