Engineering geological investigations for the feasibility study of the Earnscleugh irrigation scheme

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Paterson, B.R. 1984 Engineering geological investigations for the feasibility study of the Earnscleugh irrigation scheme. Lower Hutt: New Zealand Geological Survey. New Zealand Geological Survey report EG 383 103 p.

Abstract: The Ministry of Works and Development is carrying out a feasibility study of alternative proposals for upgrading the Earnscleugh irrigation scheme. The proposals involve distribution of water from the Clyde dam reservoir, which will augment the existing supply, and greatly increase the area under irrigation for horticultural development. Three main options were investigated: a pipeline; and high and low level races. New Zealand Geological Survey was retained to carry out an engineering geological appraisal of the various alternative routes. This involved field mapping, and shallow subsurface investigation consisting of 49 exploratory pits and 4 shafts. Numerous laboratory tests were performed on materials distributed along the routes, to determine their geotechnical properties and likely behaviour. The main rock types in the area consist of basement schist which forms the hills surrounding the alluvial terraces; pockets of Tertiary non-marine sediments and schist fan alluvium that are exposed along the western foothills; and extensive alluvial terraces. The high level race alignment traverses the foothills, well above the level of the plains, where the geology is highly variable and the terrain is more difficult. The low level race alignment and the pipeline occur at a lower level where the materials are less diverse, and the slopes are more gentle. All water races will need to be lined because of the high permeability of the gravels, and the open jointed nature of the schist. The Tertiary sediments and possibly the older fan alluvium, are potential sources of lining material. Field trials will be necessary to prove their viability