Read, S.A.L. 1976 Ohau B and C power project : dam core and canal lining investigations, Tomahawk Gully. Lower Hutt: New Zealand Geological Survey. New Zealand Geological Survey report EG 263 71 p.
Abstract: Investigations for earth dam core and blanket and canal lining for the Ohau B and C Power Project (layout on sheet 1) were commenced in April 1975. They were unsuccessful looking for Fan Alluvium on the Glencairn Fan and looking for Pre-Balmoral Outwash Gravel (Pre-BOG) at the northern end of Table Hill. Investigations at Tomahawk Gully, immediately south of the Ohau B Powerhouse, were commenced in March 1976. These latest investigations (drilling and laboratory testing) are considered successful in locating an adequate volume of suitable impermeable material for the Ruataniwha Dam and Blanket, the Ohau B Canal and part of the Ohau C Canal. This report gives the results of the investigations including; geological logs of the shafts drilled; the geological setting of the fan; material types and variations (including grading envelopes); the limits of material and volumes available and summarizes the results of laboratory testing (e.g. permeability). The assessment of the laboratory testing is given in a separate companion report by Mr D J Convery. The drilling of additional fans along the Ohau C Canal (e.g. Cairn Gully) is in progress and will be reported separately. (auth)