Kawarau River power investigations : engineering geological feasibility investigations at the KW35 damsite

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Macfarlane, D.F. 1984 Kawarau River power investigations : engineering geological feasibility investigations at the KW35 damsite. Lower Hutt: New Zealand Geological Survey. New Zealand Geological Survey report EG 387 40 p.

Abstract: The KW35 damsite has been investigated as the site for dam / intake structure to two separate, and mutually exclusive, canal options for the development of the hydroelectric power potential of the Kawarau River. The site is located within the active Nevis-Cardrona Fault System, immediately downstream of the potentially active Muddy Creek Fault. The major engineering geological features of the site are: (1) It is underlain by moderately strong, highly anisotropic, thinly laminated schist which dips steeply upstream; (2) the rockmass contains a large number of foliation shears and some low angle, downstream-dipping shears; (3) clean sandy gravels, with a mean depth of 13 m and low relative density, are present within the river channel. It is concluded that the river channel gravels should be treated or removed from the foundation area. The bedrock schist should provide an adequate foundation for a low concrete dam but further assessment of the downstream sliding stability of rock wedges bounded by low angle shears and foliation shears is required. Cut slopes in schist will be stable at 1/2 : 1 provided selective anchoring of unstable wedges is undertaken. All overburden slopes should be cut to 1/2 : 1 or flatter for long term stability. A full seismotectonic hazard evaulation of the Nevis - Cardrona Fault System is in preparation. Possible effects of a large magnitude nearby earthquake on the KW35 site include ground rupture (most likely as minor secondary displacement on shears) and ground shaking.