It might be worth noting that the Ganges/Padma, Brahmaputra, and Meghna rivers combine and drain to the sea in Bangladesh. So, a dike would need to confine not just the sea, but the combined rivers; or you would need a really phenomenal pump, probably orders of magnitude larger than has ever been constructed. It is not easy to find out the annual water flow exiting to the sea from that system. And, it is not the only one.