Pukaki high dam - groundwater conditions

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Read, S.A.L. 1974 Pukaki high dam - groundwater conditions. Lower Hutt: New Zealand Geological Survey. New Zealand Geological Survey report EG 191 24 p.

Abstract: Reports written in the past have not definitely recognized a ground water table under the Lake Pukaki outlet. This has been due to somewhat unusual groundwater conditions and a paucity of available quantitative data. This report summarises all the investigations and piezometer installations relevant to establishing the position of the existing groundwater table. The water table is 150' below the level of the present lake between R.L. 1450' and 1420' and is higher within the Contorted Sediments gravel that within the Mt John Outwash Gravel. Although the water table fluctuates, no definite cause for the fluctuations is recognised. The source of recharge water and the amount of water flowing under the lake outlet are not able to be ascertained within the data used in this report. Due to the lack of understanding of the present groundwater conditions no predictions on the future behavior of the groundwater table when the lake is raised are able to be made. A further study to the geology and permeability of materials under the downstream toe of the dam should be made to best position the relief wells downstream of the toe of the dam. (auth)