How does Deraniyagala survive the tsunami as noted in the memoir, Wave?

Deraniyagala describes the horror on her husband’s face just before the tsunami flipped the Jeep in which they were trying to outrun the strangeness they had noticed in the ocean. Deraniyagala was carried along with the churning water until she managed to grab onto a branch. This branch kept her from being swept out to the ocean in the receding waters.