Upper Waitaki Power Plans Still In Doubt

Press, Volume CVI, Issue 31097, 28 June 1966, Page 22

Upper Waitaki Power Plans Still In Doubt

Although a firm Government decision on development of the upper Waitaki river for hydro-electric production has still not been reached, extensive investigation and experimentation are continuing in the area.

Deep bulldozer cuts , have been made at > proposed dam sites to determine the nature of the material which will be used in construction, and to gauge the suitability of the sites for hydroelectric power stations. | Aerial surveys have also been carried out, and much of the ground survey work (Carried out recently has involved the setting out of ! markers for further aerial work. If the full potential of the Waitaki is developed it is estimated that the harnessed river would produce in excess of 2,500,000 KW of power for consumption throughout New Zealand. The ultimate scheme envisaged will entail control of Lakes Ohau, Pukaki, and Tekapo, and the construction of a network of canals utilising the combined flow of the lakes and leading to the head I of Lake Benmore.

A station using a head of 196 ft to produce 60.000 KW is tentatively planned for the

Maryburn Basin. This would |be fed by a ten-mile open canal from the Tekapo river, below the present generating station. A further station would be situated on the eastern shore of Lake Pukaki. It would be fed by eight miles of canal, and a mile-long tunnel taking the discharge from Maryburn. It would have an output of 120,000 KW. From Pukaki the canal water would be fed to the Ohau river through two stations established on the terraced river bank. A dam sited just above the existing Ohau bridge would form a small lake to feed the canal continuation to two further power-houses, one on the shore of Lake Benmore and one at an intermediate point. The proposed capacities of the stations would be 117,000 KW, 226.000 KW and 200,000 KW respectively.

Trial Shaft Considerable Investigation is still being carried out to establish the availability and suitability of materials for the construction of the canal. The dimensions of the canal will vary according to particular conditions, but a typi-

cal section will have a bed width of 58ft, a depth of about 16ft of water, and adequate freeboard. A trial shaft has recently been sunk into the Maryburn range to investigate the materials which will be encountered in tunnelling. The area has already been found to have unique geological problems. About a mile from Irishmans creek, a few miles along the main road from Tekapo, two trial sections of canal have been built in the last month. These will test the permeability of the material* used to line the canal sides, and also show the effect of severe temperature changes on the canal structure when it is carrying no water, as will occur at some times through the year. Geologists investigating the scheme consider that it will still be necessary to raise the level of Lake Pukaki to the same level as Lake Ohau. Lake Ohau would also be raised slightly to allow water to be channelled nut through an abandoned outlet

channel into the proposed ■ canal. Because of the seismic | nature of the area, geological investigation and preparation! has been more detailed on ( these proposals than on any previous scheme. Major fault lines run across some of the sites chosen for the canal and for the power stations, and the whole area is made up of rugged and difficult terrain. Glacial advances and gigantic land movements have left a complex and often puzzling geological pattern. The Ministry of Works recently purchased a large block of flat tussock-covered land adjacent to the highway in the vicinity of the Twizel I river. The site, which is about 36 miles by road from Otematata is considered the most likely for a new Upper Waltaki schemes’ township. If the recent proposals are implemented, the township would have a life of about 20 years, and it is estimated that at its peak, the population would be greater than that reached by Otematata.