CLYDE DAM 1977-88

Press, 1 July 1988, Page 9

CLYDE DAM 1977-88

DAVID WETHEY,

a regular

camera-toting visitor to the Clyde dam site since the 19705, has captured the gradual transition on film. Story: GLEN PERKINSON

The recent 17-week strike by 470 Clyde dam workers was one of the longest experienced in the South Island, and may well delay the completion date of what will be New Zealand’s largest hydroelectric project. That delay may cost the private venture employer as much as $97,000 each day the project runs over time. The penalty /payments were written into the contract signed between- the New ZealandGerman consortium, ZublinWilliamson. But industrial disputes have not been the only delays experienced by the joint venture.

The discovery of a fault line directly underneath the dam led to months of extra work and design problems early on in the project. Geologists consider there is a “low to very low” possibility of movement along the Dunstan Fault running upstream of the massive concrete dam. A special slip joint was. incorporated in the dam, which allows the dam to move in’ different directions by as much as two metres. Engineers knew of the faults, but in 1983 they admitted that they were more extensive than first thought.

The dam is costing more than $955 million. The Zublin-Williamson joint venture started building the left abutment of the dam in 1983. The then Ministry of Works and Development had begun excavation of the site in 1977. The M.W.D. — now Works Corporation — is building the right abutment and the powerhouse. It is also preparing the lake area. There are more than 1 million cubic metres of concrete to be poured to complete the dam, the largest gravity dam in New Zealand. The power station will initially

be capable of producing 432 megawatts of power from four turbine generators. This is expected to produce an average of 1938 gigawatts of power each year — enough to keep the cities of Dunedin and Christchurch supplied with electricity. Two more turbine generators can be added to the powerhouse, increasing the generating capacity to 610 megawatts. During the dam’s construction peak there were more than 1000 men employed on the site.

That number will continue to tail off from now until the project’s completion in about 18 months.

It was hoped to have the first power available by next year but this may now be optimistic.

The dam will be 490 m across at the crest and will rise 60m above the existing river level. The deepest foundations are set a further 40m deep. Behind the Clyde dam will form a 26sq km storage lake—- — Dunstan. Lake Dunstan will stretch 20km up the Cromwell Gorge to the township of Cromwell and then spread out over the Lowburn Flats. The old, historic, commercial area of Cromwell will be inundated. This has led to the development of a new Cromwell shopping mall which was officially opened in 1985.

Once the river diversion channel, allowing the Clutha River to by-pass the dam, is closed it will take a further three months for Lake Dunstan to fill. The Clutha and Kawarau rivers were first considered major sources of hydro-electric power in the 19405. The first dam site for the area was planned at Roxburgh, and the Roxburgh dam was commissioned in 1956 and began operating in 1963. Attention then turned to the

Clutha Valley in the 19705. Much political debate occurred about the favoured options. There were proposals to build two dams at Queensbury and Luggate, plus the single Clyde dam proposal. In 1976 the National Government opted for the single Clyde project — greater power potential and lower construction costs per unit of electricity tipped the scales in favour of the Clyde dam. Rumours indicate that Electricorp is considering also commissioning another dam at Luggate — some time in the next decade. Unions on the Clyde dam site maintain that the latest dispute was more than a money grab. It was to ensure the. rights of dam workers when the Luggate project goes ahead. The joint venture is contracted not to discuss the project publicly. The 17-week strike which ended last week, and other industrial skirmishes, have delayed the project somewhat, but, according to one Zublin-Williamson site official who spoke to “The Press,’’ the discovery of the seriousness of the river fault poses major problems for both the joint venture and the government workers.