Dam plans for the Kawarau

Press, 1 June 1984, Page 6

Dam plans for the Kawarau

Parliamentary reporter Five hydro-electric scheme options for damming the Kawarau River in Central Otago have been released by the Minister of Energy, Mr Birch, for public comment. The Kawarau Gorge between Cromwell and Queenstown represents a big hydro-electric resource but Mr Birch acknowledged that the proposals to dam the scenic and historic river were controversial. The options were being released while studies continued. These would not be completed until 1985. No work would be done on an environmental impact report or to seek statutory approvals for construction until then. A full report would also be published on details of the studies when finished, he said. This report would allow an assessment of the engineering, economic and environmental aspects of a range of possibilities. A decision would then be made on whether to continue with more detailed studies on proposals. < Originally, two

stations had been planned for the Kawarau, with a maximum output of about 1400 gigawatt hours (GWh). Because of the environmental, historic, scenic, and recreational interest in the river, and because of landslip problems into any gorge reservoirs, the 1983 Energy Plan assumed two stations with a combined output of 900 GWh. Before any decisions could be made on the Kawarau, Mr Birch said two actions were needed. A scheme had to be chosen and approved, and its economics compared with the economics of all possible electricity alternatives. The Kawarau catchment bringing water to the gorge is huge — 5500 square kilometres including Lake Wakatipu and the Shotover, Nevis, and Arrow rivers. From its confluence with the Shotover downstream to the head of Lake Dunstan, created by the Clyde dam, the Kawarau is in theory capable of generating up to 85 per cent of the electricity the Clyde scheme will generate. But hydro-electric de-

velopment of the Kawarau Gorge faces three big problems — hillside stability of the reservoirs created, the build-up of sediment, and the need for residual flows in the river. Little is known about any of the three constraints. There was too much water in the river to measure residual flow conditions last year, and another trial is planned for this year. Mr Birch said the five options had been chosen as a basis for more detailed studies. When the studies were completed, the options might need to be revised. Construction time would vary depending on which scheme was chosen, but would take from eight to 13 years, with a peak construction work-force ranging from 650 to 1150. Depending on the scheme, up to 15 million cubic metres of canal and tunnel spoil could need to be disposed of, and up to 900,000 cubic metres of concrete work built. Scheme A is the biggest option with a total annual generation of 1070 GWh. It involve only one

power station. This would mean building a 30m concrete dam at Gibbston at the upstream end of the Nevis Bluff, and a powerhouse on the southern riverbank at Gees Flat at the downstream end of the gorge. The dam would be linked by canals and a 7km tunnel passing twice under the river and then under Mount Difficulty to Gees Flat. The lake created by the dam would run upstream for about skm to Twin Bridges. Scheme B would provide 1060 GWh a year from two 30m-high dams and two powerhouses. . The first dam would be at Gibbston with a 295 m lake running back to Twin Bridges. Water would run through a race to a powerhouse on Victoria Flats. The water from the Victoria Flats powerhouse would then flow into a lake created by a second dam lkm upstream from Gentle Annie Creek. The dam would divert water into a 5.5 km tunnel under Mount Difficulty to a second powerhouse at Gees Flat.

Scheme C would provide 940 GWh a year from three dams and three powerhouses. The first would be the same as in Scheme B, with a dam at Gibbston and a powerhouse at Victoria Flats. The second would have a dam and powerhouse at Gentle Annie Creek instead of the tunnel at Gees Flat. The third dam and powerhouse would be at Gees Flat, with a 40-metre high dam creating a 6km lake, flooding the Roaring Meg confluence and the road through the gorge. Scheme D would generate 710 GWh a year from one dam, at Gentle Annie Creek, with the storage from the lake running by tunnel under Mount Difficulty to a powerhouse at Gees Flat. Scheme E would involve two dams and powerhouses, the two lower components of scheme C. The powerhouses at Gentle Annie Creek and Gees Flat would generate a total of 590 GWh a year.