The geology of the Atiamuri dam site

Abstract

The Atiamuri hydro-electric power-station is founded on the summit of a dome of vertically banded Patetere Rhyolite buried beneath rhyolitic pumice breccias and fluviatile sands and gravels. Hydrothermal solutions silicified part of the rhyolite and altered and silicified portions of the pumice breccias near the dam site. Of three prominent terrace systems the highest (RL. 910 ft) is correlated with the Hinuera terrace at Karapiro, and the second (R.L. 860 ft) results from aggradation due to pumice eruptions in the Taupo area about 130 A.D. Dam and power-house sites were selected after suitable foundations had been proved in a narrow section of the river valley that was free from major leakage channels which would be uneconomic to seal. A leakage channel on the left bank was examined and two suspected leakage channels on the right bank were disproved. A low water-table near river level extends across the dam area and indicates permeable rocks on the left bank. © Taylor & Francis Group, LLC.