Shoreline materials around the enlarged DG3 reservoir

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Thomson, R.; McKellar, I.C. 1977 Shoreline materials around the enlarged DG3 reservoir. Lower Hutt: New Zealand Geological Survey. New Zealand Geological Survey report EG 280 7 p.

Abstract: The DG3 reservoir in Scheme F drowns a much greater area of the Cromwell Gorge than that of Scheme H. As part of the environmental assesment of Scheme F, the Ministry of Works and Development asked the N.Z. Geological Survey to report on the general geology of the affected region, the geology of the DG3 Damsite and the rock types affected by the higher level reservoir. About 50% of the lake margine within the gorge will cross existent schist exposures. Most of the remaining shoreline will be in detrital materials, ranging from corse rockfall to fine colluvium and mass movement deposits. Subordinate lithologies include outwash alluvium and the fans from tributary streams. No large-scale slope instability is expected as a result of reservoir infilling, although limited slumps may occur in some materials. The most noticable effect will be the development of self-armoured beaches within the operaltional range of the reservoir and the formation of adjacent, steep, permanent scarps, slightly above the 195 m laval. The established shoreline will be rocky and compared with the lower DG3 lavel of Scheme H there will be few flat areas for recreation. Resultant visual impacts will be in strong contrast to the aesthetically pleasing landscape existing in much of the gorge at present. (auth)