Past dam disaster casts a shadow over Three Gorges.

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The Human Rights Watch/Asia report is based on articles from limited circulation Chinese hydrological journals and an unpublished 1975 investigative account by a well-regarded Chinese journalist. The report says that officials were warned about the design and management flaws, but chose instead to believe they had constructed fail-safe "iron dams." During the late 1950s, Chen Xing, one of China's foremost hydrologists, criticized the government's lack of flood control preparations in Henan province. In response, he was denounced by Communist Party officials and lost his job.

There are several ominous parallels between the disaster and the Three Gorges project. Qian Zhengying, the Minister of Water Resources who censored Chen, still presides over water projects in China, and is a leading Three Gorges promoter. And criticism of Three Gorges is no better received than were the earlier warnings; at least one prominent critic, journalist Dai Qing, has spent time in jail and is now prohibited from publishing in China. Officials have also refused to address major environmental, social, and technical concerns about Three Gorges, such as the possibility of earthquakes triggered by the weight of the water backed up behind the dam, and how to manage the silt that will flow into the reservoir.

Most disturbingly, Chinese leaders may already be discounting public safety, in their plans for Three Gorges. The normal water level of the reservoir behind the dam was to be set at 160 meters, a compromise between flood control managers, who preferred a water level of 150 meters, and power and navigation managers, who sought higher levels. Premier Li Peng had the last word, ordering the level raised to 175 meters, only 10 meters below what planners consider the maximum safe height for the dam. Ground was broken on Three Gorges in 1994. If the project is built as presently planned, a collapse would release a flood 40 times the size of the 1975 disaster.