A MAN-MADE spur juts into the mighty Jamuna river—known as the Brahmaputra upstream, over the border in India—near the town of Enayetpur. The solid wall was built, expensively, to control the massive flow of the river. But erosion now eats deep into its foundations and the river is reclaiming the land once again. Last year people lived beside it in makeshift shacks; now where their homes once stood there is only water.