Mohaka River power investigations : step three damsite (Te Hoe site) : preliminary engineering geological mapping and proposed investigations

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Hegan, B.D. 1982 Mohaka River power investigations : step three damsite (Te Hoe site) : preliminary engineering geological mapping and proposed investigations. Lower Hutt: New Zealand Geological Survey. New Zealand Geological Survey report EG 364 9 p.

Abstract: Preliminary engineering geological mapping of the Step Three damsite at Te Hoe, as part of the investigations to determine the hydroelectric generation potential of the Mohaka River, has been completed. Three potential damsites at M50, M54, and M55 are considered in the report. The geology of the area is complex and consists of a sequence of mudstones, sandstones, and in places, shelly limestones which have for the most part a N to NE strike and dip at steep to moderate angles to the east or south east. The rocks have been folded near the M55 damsite, where an upright, assymetrical anticline plunging south has been mapped. The damsites in the Mohaka River area lie within an historically active tectonic region with the active Mohaka fault system passing some 4 km from the M55 damsite. Its close proximity and the effect of strong earthquakes will need to be considered in both dam design and land stabitity. Large landslides and debris avalanches have been active in both the Mohaka and Te Hoe Rivers, particularly during historical earthquakes, and further work is necessary to investigate land stability in the area, especia11y along the reservoir margins. Future detailed geological mapping will cover all three damsites, but subsurface investigations are recommended for the M55 site only. One investigation drive and three drill holes together with seismic lines are recommended at the M55 site. (auth)