Up the Valley - the 3 Dams

Waitaki was the first power station to be built on the Waitaki River.  It was also the first station in New Zealand to be built without diverting the natural river flow.  The station was built in stages, starting with a cofferdam to divert water to the south side of the river.  Construction then began on the north side of the river, with 11 sluice gates allowing water to flow while the second section was being built on the south side.

The station’s powerhouse was completed in 1934 after the dam was built.  It was made of reinforced concrete and was 109 metres long.  The powerhouse was extended to 152 metres in the early 1950s to house the final set of generators.  The station’s first two generators were commissioned in 1935, and a third generator in 1940.  Two more generators were installed in 1941 and 1949, bringing the station to its capacity of 75MW.  In 1952, upstream from Waitaki, the Pukaki and Tekapo water storage projects were finished.  The power station took advantage of the improved water flow, extending the powerhouse to 152 metres and adding two more generators in 1954.  This increased the station’s capacity to the present-day level of 105MW.

In the 1920s, the Aviemore site was identified as a possible site for power generation.  However it wasn’t until 1961 that the Electric Power Development Board recommended Aviemore to be built.

Construction began in 1962 and presented some unusual challenges.  Because part of the dam had to be built across a fault line, it was constructed from both concrete and earth.  This was the first time this design had been used in the South Island.  A diversion tunnel was built, which took the outflow from the lake during construction.  This was New Zealand’s first large scale use of a low-heat cement, which allows a record rate of concrete to be poured without using cooling coils.  Aviemore has the largest steel penstocks (the pipes that bring the water into the powerhouse) of any power station in New Zealand.  The penstocks are 7 metres in diameter.

Benmore is the country’s second largest hydro station after Manapōuri. It generates enough electricity each year for about 298,000 average New Zealand homes. The Benmore power station is located on New Zealand’s largest manmade lake – Lake Benmore – and is New Zealand’s largest earth dam. Benmore power station was commissioned in 1965. Construction started in 1958. The lake was filled in December 1964, and the first power was produced in January 1965. Initially Benmore was going to be a concrete dam like Waitaki, but advances in dam building techniques meant Benmore was able to be built using earth. At the time of construction, the dam was the largest in the Southern Hemisphere and the project was the biggest of its kind in New Zealand. In October 1957 the plan to build the Benmore power station was approved in conjunction with the Cook Strait Cable.

Benmore straddles two South Island provinces.  The spillway, which allows excess water to pass safely through the dam, lies on the Canterbury side of the Waitaki River and the powerhouse lies on the Otago side of the river.