The worst power generation-related accident in history was the cascade failure of a series of hydroelectric dams. It killed nearly a quarter million people, damaged or destroyed 6 million buildings, and forced the evacuation of 11 million residents. Basically, it was as bad as or worse than the tsunami in Japan.
In stark contrast to nuclear accidents, it is almost never brought up as an argument against hydroelectric power.
A "once-in-2000-years" year flood is going to cause casualties whether there are hydro turbines there or not. At least that area isn't uninhabitable for centuries.