Past dam disaster casts a shadow over Three Gorges.

• Author: Tuxill, John
• Position: Dam project in China

New evidence of a catastrophic dam failure in China heightens concern over the Three Gorges project, which aims to erect the world's largest dam across the Yangtze River. According to a 1995 report by Human Rights Watch/Asia, between 86,000 and 230,000 people died in August 1975 following a massive collapse of 62 dams on the Huai River drainage in Henan province of eastern China. The collapses were also a major cause of the regional famine and epidemics that followed in the wake of the Huai floods, and which affected an additional 10 to 12 million people. The government suppressed coverage of the catastrophe in the Chinese press, and it was apparently not discovered by foreign news services.

The dams collapsed following three days of torrential rain from a typhoon of once-every-2-thousand-years magnitude. (The two largest dams that failed, Banqiao and Shimantan, were built to withstand floods of up to 1 thousand years' magnitude.) But the disaster cannot be attributed to the intensity of the storm alone: many of the dams were doomed by a combination of poor planning and management. In their haste to meet official targets for water storage, hydrological planners of the 1950s took questionable shortcuts on dam design, such as reducing the number of sluice gates - openings through which excess water can be released. Officials also neglected to implement essential flood control measures, including the construction of diversion channels and dike maintenance. And many reservoirs in the Huai basin were maintained at high water levels, so they had little excess capacity when the typhoon struck on August 5th. The fate of the largest dam, Banqiao, was sealed when managers opened the sluice gates but found them partially blocked by accumulated silt. The rising waters ultimately breached and collapsed the dam, releasing a massive wall of water that swept away entire villages.

The Human Rights Watch/Asia report is based on articles from limited circulation Chinese hydrological journals and an unpublished 1975 investigative account...