Share After a 2008 avulsion on the Kosi River, floodwaters overran the Indian state of Bihar, displacing millions of people. Prashanth Vishwanathan/Bloomberg/Getty Images Why do rivers leap from their banks? Scientists strive to predict deadly flooding events May. 13, 2021 , 2:00 PM Rumors that the Kosi River was about to burst were spreading fast in Kusaha, a Nepalese village on the border with India. The river's levees, towering over the village, were being eroded quickly by the cresting waters. At 2 p.m. on 18 August 2008, the east bank ruptured. People ran for their lives as the breach grew. Soon, the entire river, one of the largest tributaries of the Ganges River, had overrun Kusaha and was spilling into India, drowning farm after farm in search of a faster path to the sea.