Hydroelectricity has been central to meeting New Zealand’s energy needs since the early 20th century. In 1924 hydro generation was less than one petajoule (a petajoule is equal to 277.7 gigawatt-hours of electricity). From the late 1920s hydro generation dominated electricity supply; in the mid-1990s it supplied three-quarters of all electricity. In 2007 hydro generated 83.8 petajoules – 54.9% of the total electricity generated in New Zealand.
From the late 20th century environmental factors were considered increasingly important. The generation of hydroelectricity produces no carbon dioxide (a greenhouse gas) and uses a renewable resource, water. Hydro contributes a very large proportion of New Zealand’s renewable energy: in 2007 hydroelectricity supplied 82.5% of the 101.7 petajoules of energy generated from renewable sources.
The generation of hydroelectricity requires a substantial and reliable water source, and a drop in altitude – water speeds down waterways and drives turbines that generate power.
Much of New Zealand’s terrain is mountainous, particularly in the South Island. Close to three-quarters of the land is either mountainous or steep hill country, with another 15% hill or downland; only 11% is plains or plateaus.
The country has a temperate climate, and high rainfall. The long, narrow North and South islands lie roughly northeast–southwest across the path of westerly weather systems known as the roaring forties, which convey moist air across the ocean. Volcanic mountains in the central North Island, and the chain of the Southern Alps in the South Island are a barrier to moist airstreams, and cause high rainfall. These areas provide excellent catchments and run-off.
Hydro development in New Zealand involved public works, and the control and use of water rights by the state, because of the scale of developments, the high levels of financing, and the central role adopted by the state in development of infrastructure and natural resources.
The state first entered the field of electricity generation in an unexpected way – lighting up the new and booming tourist and spa town of Rotorua in 1901. On 20 May the railway station, baths and sanatorium were electrically lit for the first time, prompting one observer to say that the headlight of an incoming train ‘pale[d] into insignificance when approaching the station’.1
From the early 1880s to 1901 the state was not involved in hydro developments. In 1886 a gold-stamping battery at Bullendale in Central Otago had a small hydro plant. Hydro plants were also used in the South Island for river gold-dredging in the 1890s, and at Thames in the North Island for gold mining. Freezing works and dairy factories were powered by hydro.
In 1888 Reefton was lit by the first public supply of electric lighting, provided by a small hydro station on the Īnangahua River. In Wellington in 1889 some electric lighting was briefly provided by a hydro plant driven by the city’s water supply, before a steam-driven plant was installed.
Small municipal hydro schemes were run by local authorities or private enterprise. In Taranaki, where there were many streams to be harnessed, such schemes proliferated. The first large-scale hydro plant was at Waipori, for the city of Dunedin, in 1907 – a gorge provided an ideal site for power generation.
Central government regarded water as a public resource. In the 1890s, when entrepreneur Josiah Firth proposed to use the Huka Falls on the Waikato River for hydroelectric generation, the government moved to prevent this happening.
In 1896 Premier Richard Seddon introduced legislation to prevent the development of electrical power generation without government permission. The state gained monopoly control over water for hydro development. This served the country’s energy needs well, as it encouraged the creation of a national system, centralising planning, and aiding extension of electricity into rural areas.
In 1904 the government commissioned a survey of hydro resources. It constructed a large power station at Lake Coleridge to supply the city of Christchurch. The station began generating power in 1914.
During the First World War the government investigated large schemes in the North Island, with the intention of creating an island-wide system. Stations were planned at Arapuni on the Waikato River, Tuai, Piripāua, and Kaitawa on Lake Waikaremoana and Mangahao in the Tararua Range.
Many very small hydro plants were vital for isolated areas not yet reached by power lines. The 1934 Dawson Falls hydro station on Mt Taranaki is one of the oldest still operating unchanged.
This plan became the foundation of the country’s 20th century integrated electricity system, based on hydro power. The goal was to achieve economies of scale, with large generating plants at power sources feeding a network of high voltage transmission lines carrying electricity to centres of use.
Mangahao, in Horowhenua, was completed in 1924. The station was on the small side with an erratic water supply. Construction was difficult at the wet and inaccessible site, and frequent flooding hindered progress on the works.
Arapuni, finished in 1929, was plagued by serious engineering problems because of the geology of the area. The Lake Waikaremoana stations were built in 1929 (Tuai), 1943 (Piripāua) and 1948 (Kaitawa). In 1934 Mangahao, Arapuni and Tuai stations were interconnected into a single North Island system.
The state employed large workforces to build stations. They lived in temporary ‘hydro towns’ during the construction phase, then moved on to other hydro works.
In the second half of the 1920s increased availability of both electricity and electrical appliances led to spiralling demand. Existing electricity supply was no longer sufficient.
Government attention shifted to the South Island. Southland, with central government’s agreement, built the Monowai station in 1925, and reticulated the region, erecting power poles and lines. The government made plans for the centrally located Waitaki River, and a large station was built there by 1934. New Zealand had a fledgling national electricity generation system based on hydro power.
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.
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.
The old and small Horahora station, built by private enterprise in 1913, was submerged as the large Karāpiro 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.
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.
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.
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.
Environmental and social concerns began to make an impact on hydroelectric projects from the 1960s. The first sustained opposition to planned work occurred in relation to Lake Manapōuri.
New Zealand’s cheap and plentiful hydro resources were attractive to the electricity-hungry aluminium-smelting industry. The government signed a contract with Comalco in 1960, giving the company the right to use Manapōuri power for 99 years for a smelter at Bluff. Work on a power station began three years later.
The government proposed to raise the water level of Lake Manapōuri to ensure security of supply to the aluminium smelter. The resulting controversy became a benchmark against which public involvement in environmental issues in New Zealand would be measured.
The proposal attracted considerable opposition from the latter half of the 1960s. In the early 1970s the Save Manapōuri campaign mobilised New Zealanders who wanted to protect its pristine wild environment. Manapōuri became an election issue, and when Labour became the government in 1972 they decreed that the lake would not be raised.
A powerhouse was built deep underground, with a long tailrace tunnel, in inaccessible and rugged country. It was completed in 1971. In the late 1990s a second tailrace tunnel was bored to increase the station’s power output.
The Manapōuri Project was not just difficult politically. In 1967 alone, with 1,000 men on site, there were 223 serious accidents, and 18 men died during construction of the power station. Tunnelling was particularly hazardous – deaths occurred due to rock falls, accidents with the trains, and during drilling.
Following Roxburgh, the Clutha River was studied for added hydro potential. Up to five dams were considered, from Tuapeka below Roxburgh, to Clyde and other sites upstream of the existing station. An earth dam constructed in the late 1950s raised Lake Hāwea substantially to improve storage.
Control of the level of Lake Wānaka for storage was then considered. By the 1970s, when proposals became firmer, the public’s increased environmental awareness, and a growing tourism industry, made the process of getting projects approved far more difficult. Control of Lake Wānaka became politically impossible.
Water flow is critical to hydroelectrical generation. Droughts in 1972 and 1973 resulted in electricity rationing. Shop window lighting, neon advertising and flood lighting were all banned, and domestic users were urged to ‘save power, shower with a friend’.1
Attention began to focus on a dam at Clyde, with its height a matter of great debate. The National government decided on a high dam in 1976, and construction began in 1979. As a result of feared planning-permission delays to the project, the government passed empowering legislation in 1982 to get the dam built. The Clyde dam was finished in 1990, and commissioned in 1992 – after extensive stabilisation work in the gorge that was to become Lake Dunstan.
After 1990 there were no more large government-commissioned hydro stations. Electricity Corporation New Zealand, set up by the government in 1987, focused on improved efficiencies in generation through upgrading turbines and generating equipment, and the automation and remote control of stations. Since the commissioning of the Clyde station in 1992 there has been no substantial increase in hydro capacity in New Zealand.
A report in 1990 identified large potential hydro resources of up to 12,380 megawatts which could be exploited – 80% were in the South Island, in Canterbury, the West Coast, Otago and Southland. The report suggested it would be worthwhile to study the plentiful water resources on the West Coast (hardly developed for hydro power at all), and how they might be channelled eastwards to supplement river flows.
More than 2,000 megawatts, much of it in the South Island, was identified as having few apparent problems for development. From the perspective of the 1990 report it appeared that New Zealand would be well-served in the future, but two decades later not one of the potential schemes had been developed.
Hydro power provided 72.9% of electrical energy in 1990, but by 2007 this had dropped to 54.9%. The electricity generated by gas and coal increased substantially over this period, with a resulting increase in carbon dioxide emissions. However hydro provided 82.5% of electricity generated from renewable sources.
In the early 2000s further development of hydroelectricity was hindered by concern about negative environmental and social impacts. The effects of a large dam and new lake on the environment are often considerable, and affect local landowners and communities.
Since the debate over raising the level of Lake Manapōuri in the 1960s and early 1970s, hydro development has been politically contested. Public attitudes hardened further in the wake of the impact of the controversial Clyde dam in Central Otago.
Engineering and environmental investigations are complex, lengthy and expensive, with uncertain outcomes. Consents need to be obtained under the Resource Management Act 1991.
In 2004 a government-funded study identified a total of 2,460 megawatts (MW) of hydroelectric capacity that could potentially be developed. Potential schemes ranged from large – Waitaki (590 MW), Clutha (410 MW), Grey (350 MW), Waiau (235 MW) and Ngaruroro (135 MW) – to a number of much smaller schemes of less than 100 MW.
The schemes would add to the 5,366 MW of existing hydro capacity, and extend New Zealand’s renewable energy sources. But it remained questionable whether the schemes would be developed.
The study suggested that rather than persisting with the traditional large dam- and storage-based schemes, realistic future hydro development was likely to be smaller, using canals which diverted river water. They would be determined by the level of extraction permitted by residual river flows, sharing water for irrigation or other supply purposes, and would be integrated with the demands of other water users.
In 2003 power company Meridian Energy applied for resource consents for Project Aqua: six stations and 60 kilometres of canal on the lower Waitaki River, with a capacity of 540 MW. The project was shelved as a result of public opposition, and difficulties getting it through the consents process.
Meridian’s Project Aqua provoked strenuous opposition. It would have required the diversion of more than 70% of the river’s water, destroying wildlife habitat and 1,000 hectares of farmland, and preventing recreational and tourist use. People opposing the project included local farming families, canoeists, recreational fishers, tourists, local businesses and conservationists. Project Aqua’s cancellation highlighted the issue of how New Zealand might resolve its energy supply issues.
Meridian then promoted a smaller scheme, with less environmental impact, involving one station generating 200 to 285 MW, with a 34-kilometre tunnel on the north bank of the Waitaki River. In 2008 it was granted water-related consents, as a first stage of the project.
In 2007 the company also applied for resource consents for a dam and lake in the Mōkihinui gorge, on the West Coast, with a capacity of 65 to 85 MW.
Rival company Contact Energy announced in 2008 that it was reviewing potential large-scale hydro developments on the Clutha River.
In the 20th century New Zealand’s extensive water resources were harnessed for cheap and reliable electricity generation. Governments decided that water rights should be regulated in the interests of the country as a whole. The interaction of politics and local and environmental concerns may once again lead to further hydro developments, as the country’s energy needs continue to grow.
It is generally thought that New Zealand’s easily exploited large-scale hydro resources have largely been exhausted. Concern over the global impact of climate change may lead to a revision of this view. The environmental benefits of renewable hydroelectricity may come to the forefront.
Martin, John E., ed. People, politics and power stations: electric power generation in New Zealand, 1880–1990. 3rd ed. Wellington: Electricity corporation of New Zealand and Historical Branch, Dept. of Internal Affairs, 1998.
Rennie, Neil. Power to the people: 100 years of public electricity supply in New Zealand. Wellington: Electricity Supply Association of New Zealand, 1989.