Growth in the demand for electricity slowed during the depression of the early 1930s, then shot upwards in the latter half of the decade. By the onset of war a serious power shortage existed, which lasted into the 1950s. It led to a state-directed programme of development of water resources.
Hydroelectric development, mid-20th century
Lake Taupō had its water level controlled after 1941, and provided considerable storage because of its large size, even though its range of natural fluctuation was limited. The comprehensive development of the Waikato River, with eight hydroelectric stations, was undertaken between 1953 and 1970.
In the South Island, shortages were combated by building the very large Roxburgh station on the Clutha River, which has the country’s largest flow, in 1956. A smaller station had been built adjacent to Lake Tekapo in 1951. Lake levels at Tekapo and Pūkaki were controlled in the early 1950s. This was crucial to the use of the Waitaki River, as it was dependent on peak spring and summer snow-melt flows.
A power station was erected on the Cobb River in the Nelson region by 1944, after private enterprise failed to get it built. This was extended by 1954.
Hydro floods hydro
The old and small Horahora station, built by private enterprise in 1913, was submerged as the large Karapiro station had its dam filled in 1947. Much of Horahora’s equipment was removed, but the turbines and generators were left, and continued to turn as the water rose.
Connecting the islands
As the two islands’ networks developed, planning began for a fully integrated national system, with interconnection across Cook Strait. Growth in demand for power in the North Island could be satisfied by large-scale hydro development of South Island rivers. Maximum river flows in the two islands were complementary – in winter in the north and in spring and summer in the south. Southern lakes had huge water storage potential.
The national network was realised with the laying of the Cook Strait cable in 1965. As part of the same scheme, the South Island’s Benmore station, based on a massive earth dam on the Waitaki River, and the high voltage DC link between Benmore station and Haywards in Wellington were also completed in 1965.
Hydroelectric development, South Island, 1960s on
Benmore was followed by Aviemore in 1968, and Tekapo B on the shore of Lake Pūkaki in the Upper Waitaki in 1977, which was connected by canal to Tekapo A.
A high dam was built for Lake Pūkaki in 1977, raising the lake by 37 metres. A chain of stations – Ōhau A, B and C – were built between Lakes Ōhau and Benmore between 1979 and 1985. Lakes Tekapo and Pūkaki, with their valuable water storage, were fully utilised for hydro development.
Hydroelectric development, North Island
Full exploitation of North Island resources was also pursued. The Matahina station on the Rangitāiki River was built in 1967. The chain of eight stations along the Waikato River was completed.
Inflows to Lake Taupō – the Tongariro River, and others in the central plateau – were also targeted for development. By diverting water which had flowed to the east and west, the mean flow down the Waikato River could be increased. The Tokaanu and Rangipō stations were planned, to add generating capacity. Work began on the Western Diversion in 1964, and the entire scheme was completed in 1983 with the commissioning of the Rangipō station, following the construction of tunnels, canals, lakes and dams.