South Island, New Zealand
The spillway on the Ruataniwha Dam.
The dam forms Lake Ruataniwha and is located in the Mackenzie Basin in New Zealand's South Island.
An artificial lake, it was formed as part of the Waitaki hydroelectric project. It lies on the traditional boundary of the Canterbury and Otago provinces with the town of Twizel two kilometres to the north.
It is named after Ruataniwha Station, a large sheep station in the area, part of which was purchased by the NZ Electricity Department as the site for the township of Twizel.
The lake is approximately 4.5 km in length and covers 3.4 square km.
It was formed by the New Zealand Ministry of Works as part of the Upper Waitaki Power Project between 1977[2] and 1981 in a gorge created by the Ohau River. The gorge was blocked by the building of the Ruataniwha Dam whose crest carries State Highway 8 between Twizel and Omarama.
Lake Ruataniwha is fed by the output from the Ohau A power station and also by an overflow discharge from Lake Ohau down the normally dry bed of the Ohau River.
The lake functions as a surge reservoir for the power scheme. If, during excessive inflows into Lake Ohau which Ohau A is unable to pass or, when there has been a failure of the Ohau canal, Lake Ohau can overflow a weir into the normally dry bed of the upper reaches of the Ohau River and thus into Lake Ruataniwha. Also, if water cannot pass down the canal to Ohau B then the excess inflows into the lake can be diverted by the spillway down the bed of the lower reaches of the Ohau River to Lake Benmore. While limited the storage capacity of the lake also ensures that the flows through Ohau A do not have to be exactly matched to those through Ohau B and Ohau C.
Ruataniwha discharges through a natural gap in the dam into a canal which feeds the Ohau B power station.
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,[5] 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.
South Island, New Zealand
The spillway on the Ruataniwha Dam.
The dam forms Lake Ruataniwha and is located in the Mackenzie Basin in New Zealand's South Island.
An artificial lake, it was formed as part of the Waitaki hydroelectric project. It lies on the traditional boundary of the Canterbury and Otago provinces with the town of Twizel two kilometres to the north.
It is named after Ruataniwha Station, a large sheep station in the area, part of which was purchased by the NZ Electricity Department as the site for the township of Twizel.
The lake is approximately 4.5 km in length and covers 3.4 square km.
It was formed by the New Zealand Ministry of Works as part of the Upper Waitaki Power Project between 1977[2] and 1981 in a gorge created by the Ohau River. The gorge was blocked by the building of the Ruataniwha Dam whose crest carries State Highway 8 between Twizel and Omarama.
Lake Ruataniwha is fed by the output from the Ohau A power station and also by an overflow discharge from Lake Ohau down the normally dry bed of the Ohau River.
The lake functions as a surge reservoir for the power scheme. If, during excessive inflows into Lake Ohau which Ohau A is unable to pass or, when there has been a failure of the Ohau canal, Lake Ohau can overflow a weir into the normally dry bed of the upper reaches of the Ohau River and thus into Lake Ruataniwha. Also, if water cannot pass down the canal to Ohau B then the excess inflows into the lake can be diverted by the spillway down the bed of the lower reaches of the Ohau River to Lake Benmore. While limited the storage capacity of the lake also ensures that the flows through Ohau A do not have to be exactly matched to those through Ohau B and Ohau C.
Ruataniwha discharges through a natural gap in the dam into a canal which feeds the Ohau B power station.
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,[5] 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.