Banqiao Dam failure 1975
The deadliest flood in history caused by dam failure occurred in 1975 when China's Banqiao Dam burst. Though it was built to contain the River Ru even during rainfall as heavy as 300mm a day, rain in the wake of Super Typoon Nina surpassed that threshold. As many as 171,000 people perished in the flood.
By comparison, the deadliest flood in United States history due to dam failure, the Johnstown Flood of 1889, killed 2,200 people.