Tidal estuaries constrained by embankments in the Sundarbans have failed to respond to a >1 m sea level rise over the past 100 years since their construction. This paper shows that this has led to a disequilibrium morphology leading to channel erosion that has undermined embankments, causing mass failure, breaching and subsequent flooding during surge events. Predicted future sea level rise will exacerbate this trend and managed realignment of embankments will be needed to accommodate it. Management practices have, however, modified this underlying process of erosion. The increasing practice of severing tributary channels from the main channel using flap sluices to create freshwater storage ponds has, in many cases, reduced tidal flow in the main channels so that they are not only accreting rather than eroding, but capable of accommodating future sea level rise without erosion. In contrast, the rapid spread of salt water aquaculture in the Sundarbans, flooding previous paddy land, has led to an increase in tidal discharge and accelerated erosion of the embankments in estuary channels conveying water to the ponds. This paper concludes that existing management practices may have a more significant impact on flooding in the Sundarban than the predicted sea level rise due to global warming.