THE SAFETY of 10 of the world's most high-risk dams is set to be investigated under a major contract won last week by British consultant Gibb.
The dams, in the Central Asian republics of Kazakstan, Kyrgyzstan, Tajikistan, Turkmenistan and Uzbekistan, have been classified as risk category four by World Bank engineers. This is the worst possible classification under criteria set by the International Commission on Large Dams.
Engineers fear that a combination of lack of funds, poor maintenance and designs which give inadequate protection against earthquakes and flooding could lead to the dams collapsing or overtopping in extreme events. This could potentially cause the loss of life on a huge scale unless urgent action is taken.
Of most concern is the earth-fill Nurek dam, 80km to the east of the Tajikistan capital Dushanbe. At 300m tall and impounding a reservoir of 10.5km3, it is the largest dam in the world. Preliminary studies suggest that it could be at risk from overtopping because of the optimistic assumptions made in the flood management procedures.
Gibb executive engineer Ljiljana Spasic-Gril said: 'Nurek dam has an emergency spillway, but great reliance is also placed on low level gates and turbine flows in handling large floods.'
All 10 dams were designed in the 1960s and 1970s by Soviet design house Gidroproject. Under Soviet design standards dams had to be constructed to cope with 1 in 10,000 year floods and 1 in 500 year earthquakes. This compares with western standards which allow for maximum possible floods and 1 in 2,000 year earthquakes.
Gibb's £600,000 contract will involve detailed inspections of the dams, recommending remedial work and advising on its implementation.
In addition to the 10 man-made dams, engineers will advise on monitoring the safety of the Usoy natural dam in the Pamir mountains in Tajikistan, which retains a 60km long lake at an altitude of 3,300m. Its failure would flood a vast area covering parts of Tajikistan, Afghanistan, Uzbekistan and Turkmenistan. Because of its inaccessibility, no monitoring regime is in place.
The project is part of a wider programme to address the root causes of the overuse and degradation of the Aral Sea basin. Funding comes from the World Bank, Dutch and Swedish governments and the European Union and the contract is expected to last 17 months.