The Upper Waitaki Scheme
Notes from “People, Politics & Power Stations”
Tekapo A:
Constructed 1938-51. Head l00 feet. A 6,000-foot-long tunnel, 20 feet in diameter, takes water
from the lake to a large cylindrical concrete surge tank, penstock and powerhouse with a single
Kaplan turbine (used because of the low and varying head) and a generator of 25.2 MW. The Lake
Tekapo control works were constructed from 1951 to 1953 and involved a reinforced concrete
buttress dam, 45 feet high and 325 feet long, across the outlet to the lake, with four sluice gates.
Tekapo B:
Constructed 1970- 77. Head 146 metres. The 27-kilometre Tekapo canal, with a capacity of 120
m3/s, carries water from the tailrace of Tekapo A station at the outlet of Lake Tekapo to the Tekapo
B powerhouse. This was to be surrounded by water when Lake Pukaki was raised, and so the
building's substructure housing the generators and control room is waterproofed. There are two
1,275-metre-long steel penstocks, 4.2 metres in diameter, built in 49 sections with couplings. The
penstocks are cased in concrete below lake level. Flexible joints connect the penstocks to the
powerhouse in a 'dry well'. A special feature is the elimination of a surge tank by the use of a
vernier relief valve. The penstocks take water to two turbines that operate over a varying range,
depending upon the level of Lake Pukaki. The output of the generators varies between 76 and 90
MW but is usually stated as 80 MW, giving a total capacity of 160 MW. This station, like the three
Ohau stations, is remote-controlled by radio from Twizel.
Pukaki lake control
The Pukaki lake control works were built in the period 1946-51. They comprised 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.
Pukaki high dam:
Constructed in 1971- 77 at the outlet to Lake Pukaki. It is an earth dam, 61 metres high and 823
metres long, made of an impervious silty gravel core supported by gravel shoulders. The dam,
containing 4 million cubic metres of material, 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 old low dam was
submerged in the process. A 670-metre-long and 61-metre-wide concrete spillway with five steel
gates lies on the eastern side, and a 188-metre-long and 46-metre-wide lake outlet structure with
four steel gates on the western side. The lake is controlled over a range of 14 metres. Water is fed
into the 12-kilometre Pukaki canal, with a capacity of 560 m3/s, which leads to the Ohau A power
station. An 8.4-kilometre canal with a capacity of 200 m3/s from the Lake Ohau control structure
joins the Pukaki canal, and a 1-kilometre canal, with a capacity of 560 m3/s, takes the water from
both lakes to the power station.
Ohau A:
Constructed 1973- 79. Head 58 metres; Four 5.8-metre penstocks, 230 metres long, deliver water to
four 66 MW units, giving a total installed capacity of 264 MW. Because of technical problems the
units have been de-rated and the effective total capacity is 248 MW. From the tailrace of Ohau A
water travels along the river course and is dammed to form Lake Ruataniwha, a surge reservoir.
The main Ruataniwha dam is 240 metres long and 43 metres high and there is a low wing dam 480
metres long. Water from Lake Ruataniwha is carried 2.5 kilometres downstream to the Ohau B
station and then to Ohau C station by a 10.1 kilometre canal with a capacity of 560 m3/s.
Ohau B:
Constructed 1977-83. Head 48 metres. The four 53 MW units give a total capacity of 212 MW. Its
penstocks are 5.8 metres in diameter and 200 metres long. Water is carried by the same canal to the
Ohau C station.
Ohau C:
Constructed 1979-85. Head 48 metres. This is on the shores of Lake Benmore, and a twin of Ohau
B, with a total capacity of 212 MW.
The entire project involved shifting about 50 million cubic metres of material for canals and other
earthworks.
References & bibliography:
1
John Martin (Ed.), “People, Politics and Power Stations”, ECNZ
2
Meridian Energy Ltd brochure
3
Marion Sheridan, “Dam dwellers – end of an era”. Sheridan Press, 1995.
4
W M Duncan, “The Upper Waitaki power development – civil engineering aspects”; New
Zealand Engineering, January 1974, p 3
5
W Strauss, “The Upper Waitaki power development – a general review”; New Zealand
Engineering, January 1974, p 10
6
MWD staff, Twizel, “Power – The Upper Waitaki Hydro Power Development”. MWD,
Twizel, undated.