Over a 55-year period, the massive Waitaki hydro scheme was constructed in the middle of the South Island, and development plans are not finished yet. By Alan Titchall.
The scheme involves a massive system of man-made canals, alpine lakes – Lake Tekapo, Pukaki, Ohau, Benmore, Aviemore, and Waitaki – and rivers and generates 30 percent of the country’s hydro power. Most of it sent to the North Island through the national grid’s HVDC link.
Construction started in the late 1920s and finished in the middle of the 1980s however, further development is planned by Meridian on the lower stretches of the scheme.
Without the illustrated map with this story (see over page), you could not appreciate the sheer scale of the project. Overall, it involved shifting about 50 million cubic metres of material for canals and other earthworks over a construction period that extended from the last of the pick and shovel days to the new giant earth movers introduced to the country’s civil construction by the old Ministry of Works in the 1930s.
Constructed in multiple stages, the first part involved the Waitaki dam at the southern end of Lake Waitaki, which is the last lake before the braided Waitaki River heads for the east coast between Timaru and Oamaru.
It was built as a concrete arch dam with no spillway (but it’s designed to allow water to flow over the top if it floods).
It was built by manual labour as a ‘make work’ project during the Depression of the 1930s, with over half a million cubic metres of material excavated almost entirely by pick and shovel.
The Waitaki power station was commissioned in 1935 with two 15-megawatt generators, or enough to meet almost half of the South Island’s electricity needs at that time. These days the power station currently has six 15-megawatt generating units and generates enough electricity each year for about 62,000 average homes.
Almost 80 years old, the dam is currently being refurbished by Meridian.
First upper Waitaki scheme build
The first stage of the upper Waitaki hydro scheme at the northern end of the project (and at the southern outlet of Lake Tekapo) began when Tekapo A was built as the first of eight more hydro power stations.
Tekapo A was constructed some 1.6 kilometres below the level of the lake (and close to the Tekapo River) with work started in 1938. It was due to be completed in 1943, but construction was interrupted by a lack of manpower during World War II.
Work resumed in 1944 and the project finished in 1951. Although final control works at the outlet of Lake Tekapo weren’t finished until 1953, involving a reinforced buttress dam, with four sluice gates, to raise the lake for extra storage capability. Fully commissioned in 1955 with a 25MW capacity, Tekapo A is driven by a huge volume of water that is drawn from the lake through an intake and delivered to the power station through a 1.6 kilometre tunnel running through a small hill above what is now the Tekapo village.
Between 1958 and 1968, work was carried out on the mid-Waitaki hydro scheme, which involved the most extensive works of the entire project and the construction of one of the world’s longest high voltage direct current (HVDC) links with its two conversion Poles – one at Benmore and the other at Haywards near Wellington.
This link was the longest such transmission in the world at the time and was the start of a unified power transmission system for the whole of the country.
Pole 3, the latest incarnation of the HVDC link, and with a cost of $672 million, is due for commissioning next year.
The huge Benmore dam between Lake Benmore and Lake Aviemore, the second largest in the country, was commissioned in 1965 with a capacity of 540MW. It is the largest earth-filled dam in the country and holds back 1.25 billion cubic metres of water storage. Its construction and commissioning broke new ground in hydro technology to connect the hydro-rich Waitaki system to the energy-hungry North Island, and the project is featured in our July/August 2010 (Vol.4 No.4) issue. It can also be viewed online at www.contrafedpublishing.co.nz.
“Development of the upper-Waitaki hydroelectric scheme, with two dams and six canals (totaling 56 kilometres) began in 1970s with the construction of a 26-kilometre canal taking the discharge from the original Tekapo A station to the edge of Lake Pukaki.”
The Aviemore power station at the outlet of Lake Aviemore was also built during this period and was commissioned in 1968 with 220MW.
Second upper Waitaki scheme
Development of the upper-Waitaki hydroelectric scheme, with two dams and six canals (totaling 56 kilometres) began in 1970s with the construction of a 26-kilometre canal taking the discharge from the original Tekapo A station to the edge of Lake Pukaki, and the 160MW Tekapo B station (commissioned in 1977) between the canal and the lake.
At the same time, the original Pukaki lake control dam works (built between 1946-51 and made up of a 73-foot-high rolled-earth-fill dam with a silt core and compacted gravel shoulders, and a control-gate and spillway structure with six gates, was increased in height to 61 metres. Made of an impervious silt-gravel core supported by gravel shoulders, this dam contains four million cubic metres of material. The dam raised the lake by a further 37 metres to close to the level of Lake Ohau, allowing water to flow along the Pukaki-Ohau canal.
The Tekapo canal works are currently in the middle of extensive remedial work with a budget of over $100 million – see separate story in the September/October 2012 (Vol.6 No.5) issue.
Between1973 and 1985 the last three dams were built south of Lake Ohau – Ohau A (264MW), Ohau B (212MW), and Ohau C (212MW) on the shores of Lake Benmore.
In 2008 Tekapo A and Tekapo B stations were refurbished following the upgrades of Benmore and Waitaki.
The ones that didn’t make it
The story of the Waitaki hydro scheme is not finished yet.
Meridian Energy designed and planned another six dams on a man-made canal running from the original Waitaki Dam to the sea.
Called Project Aqua, the plan was to divert river water at the rate of up to 280 cubic metres per second into the canal, to produce about 520MW of power.
Plans hit much opposition over land issues, disruption during construction, and concerns about the sustainability of the river (and it had to get through the infamous RMA process). Meridian was working on a large-scale mitigation process, when it suddenly dropped the proposed scheme on March 29, 2004.
Up to that point, Meridian’s 2004 annual report states that the proposed scheme had cost them at least $38.7 million.
The one in mid air
In 2006 Meridian proposed its North Bank Hydro tunnel project with a single hydro scheme on the north bank of the Waitaki River. It is not dissimilar to Project Aqua, but will channel water from Lake Waitaki instead of the Waitaki River.
This $993 million project is expected to produce around 260MW by taking up to 260 cubic metres per second from the lake to a power station at Stonewall on the Waitaki River about 34 kilometres downstream.
However, the project has also been fraught with delays.
First, discovery of geological fault lines prompted a rethink of the project and a new design using a combination of canals and tunnels to divert the lake water.
Because of the complexities and cost in consenting a project of this size, Meridian was granted approval to stage the consent process, but had originally secured water consents from Environment Canterbury in 2006. Although this was appealed, in 2010 the Environment Court upheld the consents.
“We’ve made a decision to suspend the land negotiations because of the current flat demand for electricity, which means fewer new generation projects will be required in the short to medium term,” says Meridian chief Mark Binns.
“North Bank is probably New Zealand’s best hydro opportunity. It would be developed in an already heavily modified catchment, which should reduce its environmental impacts. We have got it to a stage where when we find new generation is required we can pick things up at a later time.”
Binns says Meridian shares the view of other generators that demand outlook for the next five years is “probably flat to slightly declining”.
“Our current focus is on making sure we have two to three projects ready to go so that if we need new generation we can progress these options.
“As a result, further work on land access is being suspended. We will continually review this in line with marketing conditions.”
Refurbishing an icon
Meanwhile, Meridian Energy is investing more than $40 million on a four-year project to refurbish the iconic Waitaki dam and power station, the oldest station in the overall Waitaki hydro system. The project started in April of this year.
Neal Barclay, Meridian’s general manager markets and production says, “It involves reinstating the site’s seventh generation unit, which hasn’t operated for a number of years.
“We’ll be upgrading the protection for the existing units so we can identify and rectify faults as early as possible.
“We’re also making the intersection to the site safer and carrying out erosion, seismic and flood protection work around the site.”
During the project Meridian will continue to operate within its water consents and to generate a similar amount of power, he adds.