Dam Failure Case Study: Banqiao Dam (China, 1975)

In the summer of 1975, Typhoon Nina made landfall in China near Shanghai and progressed inland until colliding with a cold front over the Henan Province, which stopped the storm’s movement. Over three days, the storm dropped over 64 inches of rainfall, including 7.5 inches in one hour, and set the world record 6-hour precipitation of 32.7 inches. This deluge caused flooding throughout the region and quickly filled to capacity any available flood storage within the region’s flood control dams.
Banqiao Dam was one of those dams. It was constructed to provide flood control and irrigation water to the region. Built in 1952, Banqiao stood 80 feet tall and was constructed of a clay core surrounded by a sand shell. The dam was designed for a 1 in 1,000 event or 20.9 inches (530mm) over three days. Typhoon Nina greatly exceeded this and was estimated to have been a 1 in 2,000 event. Due to downed communication lines and inadequate discharge capacity through its five sluice gates and undersized secondary spillway, Banqiao Dam overtopped by approximately one foot on August 8, 1975. The devastating flood wave killed tens of thousands instantly and stranded millions without access to food or clean water. In the ensuing summer heat and as a result of starvation and disease, over 100,000 more died. In addition to the terrible natural disaster brought by Typhoon Nina, the Banqiao Dam failure has been described as one of the worst man-made disasters in history.