WAIKATO RIVER, ARTIFICIAL LAKES
Seven artificial lakes (in order up stream), Karapiro, Arapuni, Waipapa, Maraetai, Whakamaru, Atiamuri, and Ohakuri, have been formed by the construction of dams on the Waikato River between Hamilton and Lake Taupo for hydro-electric generating purposes. At Aratiatia Rapids a barrage was constructed and the first of a series of machines commenced to produce power in March 1964 .
All dams have been built in narrow gorges formed at points where the Waikato River has cut into rocks of a composition harder than the bulk of the rocks forming the valley floor. The dams at Karapiro and Arapuni have been built on greywacke foundations and the lakes are in low, rolling pastoral land. Waipapa, Maraetai, and Whakamaru dams and lakes are in narrow, steep-walled gorges cut in flat sheets of volcanic rock covered by pine forests on the east bank, and by scrub-covered land recently converted to pasture on the west bank. Lakes Maraetai and Whakamaru flooded part of the forest. Up stream from Whakamaru dam, the lake is flanked by craggy, rhyolite bluffs rising 1,250 ft above lake level. Atiamuri is between two large rhyolite domes covered by pine trees, and a steep-sided volcanic spine, Pohaturoa, dominates the valley floor down stream from the dam. On the west side, up stream from Atiamuri and Ohakuri, the land rises steeply and consists of a jumbled pile of coalescing volcanic domes covered by pine forest. The low, rolling country forming the north-eastern bank has been converted recently to farm land. Lake Ohakuri drowned a small area of pasture in the Whirinaki Valley. It also flooded part of Orakeikorako hot spring area, but the raising of the lake did not extensively affect the thermal area lying above lake level – indeed it has tended to improve the activity. Aratiatia station is constructed on a partly exhumed rhyolite dome, and the lake lies within the present river channel entrenched in a flat-floored valley cut in low, rolling hills of scrubcovered volcanic rocks that are being converted to pasture.
The formation of lakes on the Waikato River has resulted in additional sporting facilities and attractive new scenic lakeside roads such as that beside Lake Whakamaru. Water ski-ing is a popular sport, and the Empire Rowing Championships have been held on Lake Karapiro.
by Bruce Newton Thompson, B.SC., New Zealand Geological Survey, Department of Scientific and Industrial Research, Otahuhu.