page_title: Waikato River
section_title: Electricity generation
hierarchical_section_title: Waikato River / Human use / Electricity generation
caption_attribution_description: English: Photo Image of the Ohakuri dam. Taken: 2004-08-26. Photographer: en:User:Seriocomic.
context_page_description: The Waikato River is the longest river in New Zealand, running for 425 kilometres through the North Island. It rises in the eastern slopes of Mount Ruapehu, joining the Tongariro River system and flowing through Lake Taupo, New Zealand's largest lake. It then drains Taupo at the lake's northeastern edge, creates the Huka Falls, and flows northwest through the Waikato Plains. It empties into the Tasman Sea south of Auckland, at Port Waikato. It gives its name to the Waikato region that surrounds the Waikato Plains. The present course of the river was largely formed about 17,000 years ago. Contributing factors were climate warming, forest being reestablished in the river headwaters and the deepening, rather than widening, of the existing river channel. The channel was gradually eroded as far up river as Piarere, leaving the old Hinuera channel through the Hinuera Gap high and dry. The remains of the old river path can be clearly seen at Hinuera where the cliffs mark the ancient river edges. The river's main tributary is the Waipa River, which has its confluence with the Waikato at Ngāruawāhia.
  The name Waikato comes from the Māori language and translates as flowing water.
context_section_description: The Waikato's first hydro-electric power station was the Horahora Power Station, now located under the Horahora bridge deep beneath the surface of Lake Karapiro. Horahora was built to supply electricity for the Martha gold mines at Waihi.
  The river has a series of eight dams and nine hydro-electric power stations that generate electricity for the national grid. These were constructed between 1929 and 1971 to meet growing demand for electricity.
  The power scheme begins at Lake Taupo, which has control gates to regulate the flow of water into the river. Once released through the gates it takes over 18 hours for the water to flow to the last power station at Karapiro. On its journey downstream it passes through power stations at Aratiatia, Ohakuri, Atiamuri, Whakamaru, Maraetai, Waipapa, Arapuni and Karapiro.
  Approximately 4000 gigawatt hours (GWh) of electricity is generated annually by the scheme, which is around 13% of New Zealand's total electrical generating capacity.
  
  The river also provides cooling water for the coal/natural gas fired thermal power station at Huntly. The power station uses river water as a cooling medium for the old steam units, which means that large quantities of warm water is returned to the river. To limit environmental impacts, conditions are imposed by its resource consent, specifying the quantity of water that can be removed by the station along with the maximum temperature of the water when returned to the river, 25 °C (77 °F). These conditions mean that output of the older steam units can be restricted, especially on very hot summer days. In 2006, a cooling tower was installed. This allows one 250 MW unit to run at full load even during such times.
caption: The Ohakuri Dam midway between Taupo, Rotorua and Hamilton
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