New York Times: The rivers that course down from the Himalayas and into this crowded delta bring an annual tide of gift and curse. They flood low-lying paddies for several months, sometimes years, at a time. And they ferry mountains of silt and sand from far away upstream. Most of that sediment washes out into the roiling Bay of Bengal. But an accidental discovery by desperate delta folk here may hold clues to how Bangladesh, one of the world’s most vulnerable countries to climate change, could …