Coastal Tide and its Interaction with the Sea Level Rise – The Case of Bengal Delta

Abstract:

The sea level rise induced by global warming is all but certain. Its magnitude will spatially vary due to thermo- and halo-steric differences and dynamical processes. At estuary scale, the variability is further modulated by the interaction with the local topography due to alteration of the tidal properties. Bengal delta is an interesting case of macro tidal delta, which is subject to a marked coastal flooding hazard and one of the most vulnerable to the impacts of sea level rise. Here we investigate the interaction of sea level rise on tide, which is the largest source of variability of sea level along this delta coastlines. Through a comprehensive hydrodynamical modeling framework comprising the coastal delta, the major estuaries, as well as the intricate hydraulic network of the delta, we assess the future changes of tidal properties to be expected for various sea level rise scenarios, representative of the end of the 21st century and beyond. We show that this effect is large, and regionally dependent. Over both the south-western and south-eastern parts of the delta, the amplitude of the tide is expected to increase when the sea level is higher, which is bound to aggravate the tidal flooding hazard. In contrast, the central part of the delta will potentially experience massive flooding of river banks and adjoining lands in the scenarios exceeding 0.5m of sea level rise. Consequently, this flooding induces a decay of the tidal amplitude in the central part. Our study shows that the tidal modulation is a significant ingredient that needs to be accounted for in the evolution of the future hydrodynamics of tide-dominated deltas. The tidal amplification may have a dominant role in the evolution of inland saline front. The friction-dominated and regionally contrasting damping and amplification mechanism also underscores the potential application of managed realignment strategy for a sustainable delta management in the future.