The Banqiao Dam failed to handle a 'once-in-2,000-years flood,' but additional construction could have spared thousands of lives.

Location: Zhumadian City, China

Cost: N/A

Constructed: 1951-1952, further work in 1954

Issue: Record flooding, lack of overflow options

Date of incident: August, 1975

The deadliest structural failure in history occurred in China when the supposedly unbreakable "Iron Dam" in Zhumadian city burst in 1975.

Built in the early 1950s, the dam was built under supervision by Soviet engineers. A flood in 1954 forced the government to extend their existing dams, including a 3-meter addition to the Banqiao Dam walls.

When cracks started to appear in the dam, they were repaired with advice from the Soviets again, and additional reinforcements were added. The engineers claimed that the dam could withstand a "once-in-1,000-years flood."

The chief designer of the dam, Chen Xing, was vocal that the design was flawed, though. He recommended 12 gates to handle the overflow, but he was ignored, and only five gates were built. Other dams in the same system had similar reductions.

As a result, in 1975, record rainfall of nearly 7.5 inches of rain per hour (almost 42 inches a day) strained the dam to its limit. Requests to open the dam and relieve pressure were rejected due to flooding elsewhere. After another two days of rain, the dam broke.

Thousands died in the initial flooding. The government intentionally destroyed several other dams with air strikes to divert the water and reduce damage, but it was too late: Thousands more died, and those who survived suffered from famine and disease without food or shelter. A total of more than 200,000 people died as a result of the catastrophe.