Banqiao Dam

The Banqiao dam and Shimantan Reservoir Dam (|t=|p=}}) are among 62 dams in Zhumadian Prefecture of China's Henan Province that failed catastrophically or were intentionally destroyed in 1975 during Typhoon Nina.

The dam failure killed an estimated 171,000 people; 11 million people lost their homes. It also caused the sudden loss of 18 GW of power , the equivalent of roughly 9 very large modern coal fired power stations or about 20 nuclear reactors, equalling about 1/3 the peak demand on the UK National Grid.

History

The Banqiao dam was begun in April 1951 on the Ru River with the help of Soviet consultants as part of a project to control flooding and to generate electricity. It was a response to severe flooding in the Huai River Basin in 1949 and 1950 . The dam was completed on June 1952. Because of the absence of hydrology data, the design standard was lower than the standard. After the 1954 Huai River great flood, the upstream reservoirs including Banqiao were extended, constructed and consolidated. Banqiao Dam was increased in height by three meters. The dam crest level was 116.34 meters above sea level and the crest level of the wave protection wall was 117.64 meter above sea level. The total capacity of reservoir was 492 million m³ (398,000 acre feet), with 375 million m³ (304,000 acre feet) reserved for flood storage. The dam was made of clay and was 24.5 metres high. The maximum discharge of the reservoir was 1742 m³/s.

Cracks in the dam and sluice gates appeared after completion due to construction and engineering errors. They were repaired with the advice from Soviet engineers and the new design, dubbed the iron dam, was considered unbreakable.

Chen Xing was one of China's foremost hydrologists and was involved in the design of the dam. He was also a vocal critic of the government dam building policy, which involved many dams in the basin. He had recommended 12 sluice gates for the Banqiao Dam, but this was scaled back to five. Chen Xing was criticized as being too conservative. Other dams in the project, including the Shimantan Dam, had a similar reduction of safety features and Chen was removed from the project. In 1961, after problems with the water system surfaced, he was brought back to help. Chen continued to be an outspoken critic of the system and was again removed from the project.

1975 Flood

The Dam was designed to survive a once-in-1000-years flood (300 mm of rainfall per day). In August 1975, however, a once-in-2000-years flood occurred, and poured more than a year's rainfall in 24 hours (new records were set, at 189.5 mm rainfall per hour and 1060 mm per day, exceeding the average annual precipitation of about 800 mm), which weather forecasts failed to predict, produced by the collision of Super Typhoon Nina and a cold front. Communication to the dam was largely lost due to the collapse of buildings under heavy rain and wire failures. On August 6, a request to open the dam was rejected, because of the existing flood in downstream areas. On August 7, however, the request was accepted, but the telegrams failed to reach the dam.

The sluice gates were not able to handle the overflow of water, partially due to sedimentation blockage. On August 7 at 21:30, the People's Liberation Army Unit 34450 (namely the 2nd Artillery Division in residence at Queshan county), which was deployed on the Banqiao Dam, sent the first dam failure warning via telegraph. On August 8, 0:30, the smaller Shimantan Dam, which was designed to survive a 1-in-500-year flood, failed to handle more than twice its capacity and broke upstream, only 10 minutes after Unit 34450 sent a request that would open the Banqiao Dam by air strike. A half hour later, at 1:00, water at the Banqiao crested at the 117.94 m level above sea level, which was 0.3 meter higher than the wave protection wall on the dam, and it too failed. This precipitated the failure of 62 dams in total. The runoff of Banqiao Dam was 13,000 m³ per second in vs. 78,800 m³ per second out, and 701 million tons of water were released in 6 hours,

After the flood, a summit of National Flood Prevention and Reservoir Security at Zhengzhou, Henan was held by the Department of Water Conservancy and Electricity, and a nationwide reservoir security examination was performed after this meeting. Chen Xing was again brought back to the project and aided in clearing the river channels.

Casualties

See also

References

External links

Category:Buildings and structures in Henan Category:Dams in China Category:Floods in China Category:Dam disasters Category:1975 disasters Category:1975 floods Category:Disasters in China