Summary of the geological investigations in the lower Waitaki River, Vol. I: geological logs of drillholes BHLW 1 to 45 and 49 to 51 to accompany a report - (summary of the geological investigations in the lower Waitaki River), Vol. II

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Mansergh, G.D. 1973 Summary of the geological investigations in the lower Waitaki River, Vol. I: geological logs of drillholes BHLW 1 to 45 and 49 to 51 to accompany a report - (summary of the geological investigations in the lower Waitaki River), Vol. II. Lower Hutt: New Zealand Geological Survey. New Zealand Geological Survey report EG 161 96 p.

Abstract: The extent of geological investigations to date for the Lower Waitaki Power Development project is presented. Discussion is centred around four areas, that between Waitaki Dam and Kurow, Kurow Island, the area between Kurow and Black Point, and Black Point. No investigations have been done downstream of Black Point. In the Waitaki Dam-Kurow section a number of faults are recognized from aerial photographs and crush zones from surface mapping and drill hole data. It is suggested that the river follows a system of major crush zones. Contours have been drawn on the basement rock/alluvium contact at the proposed intake site and it is suggested that there may be in excess of 50 ft of relief on this surface in the river bed. Seismic evidence suggests that on Kurow Island rock may come within 40 ft of the surface at the southern end of the island and that the rock is probably crushed. Drill hole data shows that there is more than 120 ft of alluvium at the northern end of the island. Between Kurow and Black Point seismic evidence suggests that at most places the alluvium is over 400 ft thick, but at one point near Waikaura, rock interpreted as schist, may come within 40 ft of the surface. Evidence from water levels recorded in a number of domestic wells over this section indicate that the Waitaki River maintains the groundwater supplies in the alluvium, and it is recommended that a study be made to determine the minimum flow past Waitaki Dam necessary to maintain groundwater at a reasonable level and also maintain a flow in the river. At Black Point the valley is bounded by two faults and Tertiary Coal Measures lie between these two faults with only a thin cover of alluvium. (auth)