Tropical storm Nina reached typhoon intensity on August 2 1975. It battered the central mountains of Taiwan, made landfall over southern China and moved northwest before turning south and dissipating. However, over the province of Henan, the collision of the typhoon’s warm, humid air with a cold front produced a series of disastrous storms which, in three days, dropped more than a year’s rain.
A 1950’s project to control flooding and generate electricity had dammed rivers in the Huai Valley Basin. After the cracks which appeared in the structure of the largest dam, the Banqiao, had been repaired, it was known as the ‘iron dam’. It had been designed to hold around 500 million cubic meters of water and to survive a ‘one in year flood’ – 30 cm (12 in) rain per day. The rainfall Typhoon Nina delivered, however, was a ‘one in 2,000 year flood’ as a record amount – over 1 m (3 ft) – fell in 24 hours.
Flooding was inevitable and all forms of communication were wiped out by the appalling weather. The order to open the sluice gates was not received and only part of the area was evacuated. All the reservoirs were filled to capacity and at 00.30 on August 8, water topped the smaller Shimantan Dam and surged through. Half an hour later came the catastrophic failure of the Banqiao Dam, and a massive, fast-moving wall of water 13 km (8 mi) wide inundated towns, villages and farmland. In all, 62 dams failed or were breached to control flooding. Thousands of people drowned and even more died subsequently from famine and epidemics – nine days later, over a million survivors were still cut off by the floodwaters.
When: August 8 1975
Where: Henan Province, China
Death toll: 25,000 from flooding, 135,000 subsequently (Henan Province Hydrology Department figures).
You should know: Eminent hydrologist Chen Xing recommended 12 sluice gates at the planning stage of the Banqiao Dam; it was built with only five, and other dams also had reduced safety features. Chen was ‘removed’ from the project for his outspoken criticism.