Lower Clutha power investigations : engineering geological feasibility assessment of the proposed Dumbarton Rock development options

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Macfarlane, D.F. 1986 Lower Clutha power investigations : engineering geological feasibility assessment of the proposed Dumbarton Rock development options. Lower Hutt: New Zealand Geological Survey. New Zealand Geological Survey report EG 395 63 p.

Abstract: Engineering geological investigations have been carried out assess the feasibility of the two proposed Dumbarton Rock power development options: (1) a dam and powerhouse at Dumbarton Rock with associate tailrace deepening of the downstream river channel; (2) a dam at Dumbarton Rock with a canal to a powerhouse on the left bank, about 4-5 km downstream. The investigations indicate that the dam/powerhouse option minimises rock excavation volumes and potential problems with thick, unconsolidated, gravels in the river channel. Careful batter design will be necessary to ensure that the river bank along the deepened river channel remain stable under operatin conditions. No major geological problems would be encountered along the proposed canal or at the downstream powerhouse (Option 2) but optimum selection of the canal inlet site to minimise potentially adverse geological conditions would greatly increase excavation volumes and therefore costs. No significant stability problems are expected along the reservoir and it is shown that reservoir impoundment will not affect existing groundwater conditions in the Roxburgh East Coalfield. Although a major regional fault (the Teviot Fault) passes immediately west of the proposed damsite, no Late Quaternary fault traces are known to occur within 15-20 km of the site and the seismotectonic hazard is assessed as very low. Construction materials are readily available at the site area. (auth)