Water power, more commonly called hydro-power, is power derived from the energy of falling water and running water, which may be harnessed for useful purposes. Since ancient times, hydro-power has been used for irrigation and the operation of various mechanical devices, such as watermills, sawmills, textile mills, dock cranes, domestic lifts, power houses
and paint making.
Since the early 20th century, the term has been used almost exclusively in conjunction with the modern development of hydroelectric power. Hydro-power is a renewable energy source.
Hydroelectric power is produced by the force of falling water. The capacity to produce this energy is dependent on both the available flow and the height from which it falls. Building up behind a high dam, water accumulates potential energy. This is transformed into mechanical energy when the water rushes down the sluice and strikes the rotary blades of a turbine. The turbine's rotation spins electromagnets which generate current in stationary coils of wire. Finally, the current is put through a transformer where the voltage is increased for long distance transmission over power lines.
Advantages to hydroelectric power:
• Fuel is not burned so there is minimal pollution
• Water to run the power plant is provided free by nature
• Hydropower plays a major role in reducing greenhouse gas emissions
• Relatively low operations and maintenance costs
• The technology is reliable and proven over time
• It's renewable - rainfall renews the water in the reservoir, so the fuel is almost always there
Hydropower is does not pollute the water or the air but does have environmental impacts:
• Hydropower facilities can have large environmental impacts by changing the environment and affecting land use, homes, and natural habitats in the dam area
• Hydroelectric dams and reservoirs may obstruct fish migration and affect their populations
• Operating a hydroelectric power plant may also change the water temperature and the river's flow which may harm native plants and animals in the river and on land
• Reservoirs may cover people's homes, important natural areas, agricultural land, and archaeological sites, which can require relocating people
• Methane, a strong greenhouse gas, may also form in some reservoirs and be emitted to the atmosphere
Hydroelectric power in New Zealand has been a part of the country’s energy system for over 100 years and continues to provide more than half of the country’s electricity needs. Early schemes such as the Waipori scheme commissioned in 1903 and the Lake Coleridge power station commissioned in 1914 established New Zealand’s use of renewable hydro energy.
By the early 1960s, most North Island hydro sites had been developed while the South Island still had plenty of potential sites. The commissioning of the HVDC Inter-Island link in 1965 made it possible to send large amounts of electricity between the two islands, and from this point onwards, hydro capacity in the South Island increased rapidly. Major developments included the Benmore power station (1966), the Manapouri power station (1971), the Upper Waitaki River Scheme (1977–85) and the Clyde Dam (1992).
In 2012, hydro generation produced 53% of the total electricity generated. The percentage of New Zealand's electricity provided by hydro generation has declined from approximately 70% to just above 50% over the last two decades. In Hawke's Bay, there is one hydroelectric power scheme, the Waikaremoana Power Scheme, located between Te Urewera National Park and Wairoa, along the upper 7km of the Waikaretaheke River. It comprises three power stations – Kaitawa, Tuai and Piripaua.
Water is taken from Lake Waikaremoana via tunnels to Kaitawa Power Station, before being discharged into Lake Kaitawa. Water is then passed through Tuai Power Station and discharged into Lake Whakamarino. From there, water is carried by tunnel to Piripaua Power Station and is discharged into the Waikaretaheke River.