Construction
Before construction of the dam could start the Ohau River was diverted by cutting a channel through a low, rocky extension of the Benmore Range and building three diversion gates there which consumed 100,000 cubic metres of concrete. The Ohau River was diverted in August 1980 so that water passed through Ohau A and then back down the river bed. Later that year, downstream of Ohau A, the river was again diverted, this time away from its natural channel and through the completed gates. An earth dam with gravel shoulders was then built on its upstream and downstream sides. The main dam, which blocks the original river channel, is 240 metres long while an adjoining wing dam is 480 metres. When the dam was completed the diversion gates were closed which, beginning in March 1982, impounded the water behind the dam up to and over a temporary weir which had been built downstream of Ohau A. In 1984 the lake was temporarily lowered by 3 metres while this weir was removed to improve the performance of the Ohau A power station. The diversion gates now function as spillway gates to allow excess water to pass safely through the dam. The lake was officially opened on Saturday 24 April 1982. There was a weekend event which attracted 7000 spectators with the rowing course hosting a regatta attended by 188 crews and representing 80 South Island rowing clubs.
Read more about this topic: Lake Ruataniwha
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