UNIQUE DEVELOPMENT OF WAITAKI

Press, Volume CIX, Issue 32072, 21 August 1969, Page 7

UNIQUE DEVELOPMENT OF WAITAKI

The full development of the Waitaki River for hydro-electric power purposes is indicated in a large model of the area shown by the Ministry of Works at the Industries Fair.

This shows not only the planned development of the Upper Waitaki, but the proposed development of the lower Waitaki with a series of 10 power stations linked by a canal.

The whole scheme will be unique, and will hold much world interest. The possibilities of the Waitaki catchment for hydro - electricity development were discussed as early as 1904 when Mr P. S. Hay, superintending engineer of the Public Works Department (now the Ministry of Works), reported on New Zealand’s water resources. With its tributary rivers, the Waitaki River has a

catchment area of 4565 square miles, second to that of the Clutha, the largest river in New Zealand. - Its alpine watershed is 50 miles long. It drains in its upper basin the glacier Lakes Ohau, Tekapo and Pukaki. The river is 106 miles long and falls 2300 ft in that distance. New Dam When fully developed, the Waitaki basin could produce about 11,500 GWh a year (a gigawatt hour is one

million kWh, or kilowatt hours). This is equivalent to about 94 per cent of New Zealand’s 1967 requirements. The development to date has been, in order:— Waitaki station, Tekapo station, Lake Pukaki and Lake Tekapo control, Waitaki station extensions, Benmore station and Aviemore station. Control of Lakes Pukaki and Tekapo which permits the storage of water for winter use has significantly increased the use of river flows at the Waitaki station. It is proposed to build a new dam and outlet works at Lake Pukaki, raise the lake more than 100 ft and double the total water storage in the basin. This should result in the long-term use of water approaching 93 per cent and make major changes in the level of Lake Ohau unnecessary. Four Machines Construction of the Waitaki station began in 1928 and the station came into use in 1935 with four machines. A fifth was commissioned in 1949 and the station developed to its originally designed capacity of 75,000 kW. Two more machines were added in 1954, bringing the capacity of the station to 105,000 kW. A single unit of 25.2 mW, Incorporated in the control works at Lake Tekapo, came into use in 1951. The powerhouse on the right bank of the Tekapo River is supplied from the lake by a tunnel a mile long. A control structure for storing snow melt from the mountain catchment was completed in 1954. The Benmore station started in 1958 and produced its first electricity from one machine in January, 1965. The interisland submarine cable was opened officially in May, 1965, when the station’s capacity was 220 mW from three machines. Three more machines were completed that year to bring Benmore to its full capacity, 540 mW. It is the largest electricity generating station built in New Zealand so far. The dam at Benmore took four years to build. It contains 16 million cubic yards of earth and rock. Building

the dam involved excavating, hauling and placing 30 million tons of material. The crest, along which a road runs, is 2700 ft long and 36ft wide, the width at base 1600 ft and the maximum height 360 ft. Behind the dam is the largest artificial lake in New Zealand, 30.5 sq miles with a shoreline of 72 miles. Three Cables A 500,000-volt direct current transmission line 354 miles overland and 25 miles under the sea was required to convey electricity from Benmore to the Haywards sub-station (15 miles north of Wellington). From Haywards the electricity is fed into the North Island grid. The three submarine cables, one of which is a spare, were laid 1000 ft apart and run from Fighting Bay in the Marlborough Sounds to Oteranga Bay, south-west of Wellington. The cable has the highest submarine capacity in the world. A factory was specially built in England to make it and a freighter, the Photinia (10,000 tons), converted to a cable-layer to place it. The total cost of the scheme was s97m, including s6Bm for Benmore station, slom for the transmission line and $5.5m for the cable. Aviemore, estimated to cost s44m, began generating power in 1968 when the installed capacity was 110 mW. It will reach its full generating capacity in 196970 with 220 mW. The four

55 mW units are the biggest hydro-generators in New Zealand. The generating capacity of Benmore is 540 mW and Roxburgh, on the Clutha, 320 mW. (Manapouri will provide 200 mW to the national grid in 1970-71 and 390 mW after that, additional to the supply for the alumina smelter. It has a developable capacity of about 700 mW). The dam at Aviemore con-

sists of a concrete section and an earth wing. The concrete section abuts on to a rock face on the Canterbury side of the Waitaki River and incorporates intakes, penstocks and spillway. It is 186 ft high, 1100 ft long and contains about a million tons of concrete.

Earth Wing The earth wing extends from the Otago end of the concrete section to near the Oamaru-Omarama highway. It is 1500 ft long, with a clay core supported on both

sides by shouldfers of sand, gravel and rook, and contains 1.5 m cubic yards of material. The water to drive the

turbine will enter the powerhouse through four penstocks, each 120 ft long and 23ft diameter. The new Pukaki high dam will increase water power storage and raise the level of Lake Pukaki. The raised lake will also conserve the energy of Tasman River flows for electricity production at the Ostler project The dam is under investigation and firm design is in hand. The Power Planning Committee has recommended that it be completed in 1973. Some firm design is in hand for the MaryburnPukaki project. This project . involves building a canal from the tailrace of the Tekapo station to divert the outflow from Lake Tekapo across country into Lake Pukaki, developing 500 ft head en route. Two new stations will be fed by the canal; one on the shore of Lake Pukaki and the other, Maryburn, at an intermediate point. The flow will be carried through the Mary Range by a tunnel a mile long. Typical Section Investigations are being made in the area to establish the of materials for building' the canal, a typical section of which would be 58ft wide, at its bed, and 16ft deep;, with sufficient freeboard. The two stations —Maryburn with an estimated installed capacity of 62 mW, and Pukaki 94 mW —have been recommended by the Power Planning Committee for commissioning in 1976. The next phase covers the

Pukaki-Ohau area where the construction of three powerhouses—Ostler, Ohau No. 1 and No. 2—is envisaged. The Ostler station, with an estimated installed generating capacity of 264 mW, would be fed by the outflows from Lakes Tekapo, Pukaki and Ohau. The Ohau stations (No. 1 of 224 mW and No. 2 of 200 mW) would complete the Upper Waitaki development down to Lake Benmore.

Partly Overlap Depending on the growth of the electricity load, the Lower Waitaki development could follow that of the Upper Waitaki, or partly overlap it. It is envisaged that 600 ft head of water below the Waitaki station could be developed by a series of 10 stations, each of 60ft head, linked by a canal 40 miles long built in the riverbed close to the Otago bank. Present estimates are that each station could generate 410 GWh a year from an

installed generating capacity of 68 mW. Investigations, civil engineering design and construction on the Waitaki River have been carried out by the Ministry of Works for the New Zealand Electricity Department A township was built at Otematata for the workforce engaged on Benmore and Aviemore. At one time it had a population of 3500, with a district high school (540 pupils), junior school (430) and two play centres (60). At peak, the workforce of the Ministry of Works and its contractors on both projects was 1650. With Benmore finished the force employed on Aviemore was (October, 1967) 997. Another construction township will be needed for workers on the Upper Waitaki development. Establishment of this township, to be known as Twizel, has begun on the Ruataniwha farming station near the Twizel River in the Mackenzie Basin. It is halfway between Lakes Pukaki and Ohau, and 36 miles above Otematata.