95-835: The Matahina power station is a hydroelectric power facility in Bay of Plenty in New Zealand on the Rangitaiki River downstream of the Aniwhenua Power Station . The river was dammed to form Lake Matahina from which water is drawn and diverted through the power station before being discharged back into the river. The Matahina dam is the largest earth embankment dam in the North Island of New Zealand. The Ministry of Works (MOW) investigated all possible sources of hydro-electric power in New Zealand. With
190-745: A greenhouse gas . According to the World Commission on Dams report, where the reservoir is large compared to the generating capacity (less than 100 watts per square metre of surface area) and no clearing of the forests in the area was undertaken prior to impoundment of the reservoir, greenhouse gas emissions from the reservoir may be higher than those of a conventional oil-fired thermal generation plant. In boreal reservoirs of Canada and Northern Europe, however, greenhouse gas emissions are typically only 2% to 8% of any kind of conventional fossil-fuel thermal generation. A new class of underwater logging operation that targets drowned forests can mitigate
285-463: A low-head hydro power plant with hydrostatic head of few meters to few tens of meters can be classified either as an SHP or an LHP. The other distinction between SHP and LHP is the degree of the water flow regulation: a typical SHP primarily uses the natural water discharge with very little regulation in comparison to an LHP. Therefore, the term SHP is frequently used as a synonym for the run-of-the-river power plant . The largest power producers in
380-414: A corresponding horizontal acceleration of 1.25g (equivalent to 2.7 metres (8.9 ft) of horizontal shear and vertical peak acceleration of 1.35g (equivalent to 1.3 metres (4.3 ft) of vertical shear) and 3 metres (9.8 ft) of oblique slip on the fault. The evaluation determined that a full displacement event could occur on any of the traces. This SEE could cause a rupture of the impervious core of
475-516: A damage survey had disclosed while there had been damage, the dam was secure and there was no cause for concern. The crest of the dam spread a little in the shaking, while minor cracking was apparent near each abutment in the road traversing the crest. A subsequent survey found that downstream displacement varied from zero at the abutments to 268 millimetres (10.6 in) at the centre of the crest. Settlement in rockfill shoulders continued for some weeks afterwards, reaching 102 millimetres (4.0 in) in
570-421: A flood and fail. Changes in the amount of river flow will correlate with the amount of energy produced by a dam. Lower river flows will reduce the amount of live storage in a reservoir therefore reducing the amount of water that can be used for hydroelectricity. The result of diminished river flow can be power shortages in areas that depend heavily on hydroelectric power. The risk of flow shortage may increase as
665-538: A key element for creating secure and clean electricity supply systems. A hydroelectric power station that has a dam and reservoir is a flexible source, since the amount of electricity produced can be increased or decreased in seconds or minutes in response to varying electricity demand. Once a hydroelectric complex is constructed, it produces no direct waste, and almost always emits considerably less greenhouse gas than fossil fuel -powered energy plants. However, when constructed in lowland rainforest areas, where part of
760-809: A large natural height difference between two waterways, such as a waterfall or mountain lake. A tunnel is constructed to take water from the high reservoir to the generating hall built in a cavern near the lowest point of the water tunnel and a horizontal tailrace taking water away to the lower outlet waterway. A simple formula for approximating electric power production at a hydroelectric station is: P = − η ( m ˙ g Δ h ) = − η ( ( ρ V ˙ ) g Δ h ) {\displaystyle P=-\eta \ ({\dot {m}}g\ \Delta h)=-\eta \ ((\rho {\dot {V}})\ g\ \Delta h)} where Efficiency
855-451: A larger amount of methane than those in temperate areas. Like other non-fossil fuel sources, hydropower also has no emissions of sulfur dioxide, nitrogen oxides, or other particulates. Reservoirs created by hydroelectric schemes often provide facilities for water sports , and become tourist attractions themselves. In some countries, aquaculture in reservoirs is common. Multi-use dams installed for irrigation support agriculture with
950-438: A leakage-resistant downstream buttress which would prevent internal erosion of the core and inner transition from leading to accelerated piping of the dam or collapse of the dam crest. This buttress incorporates a filter, transition and drain zones, an enlarged rockfill shell, and a zone of oversize rockfill at the toe. The crest of the dam was widened, and was raised by 3 metres (9.8 ft) to 82.2 metres (270 ft)RL, so that
1045-592: A positive risk adjusted return, unless appropriate risk management measures are put in place. While many hydroelectric projects supply public electricity networks, some are created to serve specific industrial enterprises. Dedicated hydroelectric projects are often built to provide the substantial amounts of electricity needed for aluminium electrolytic plants, for example. The Grand Coulee Dam switched to support Alcoa aluminium in Bellingham, Washington , United States for American World War II airplanes before it
SECTION 10
#17327877109241140-548: A relatively constant water supply. Large hydro dams can control floods, which would otherwise affect people living downstream of the project. Managing dams which are also used for other purposes, such as irrigation , is complicated. In 2021 the IEA called for "robust sustainability standards for all hydropower development with streamlined rules and regulations". Large reservoirs associated with traditional hydroelectric power stations result in submersion of extensive areas upstream of
1235-540: A result of climate change . One study from the Colorado River in the United States suggest that modest climate changes, such as an increase in temperature in 2 degree Celsius resulting in a 10% decline in precipitation, might reduce river run-off by up to 40%. Brazil in particular is vulnerable due to its heavy reliance on hydroelectricity, as increasing temperatures, lower water flow and alterations in
1330-448: A small TV/radio). Even smaller turbines of 200–300 W may power a few homes in a developing country with a drop of only 1 m (3 ft). A Pico-hydro setup is typically run-of-the-river , meaning that dams are not used, but rather pipes divert some of the flow, drop this down a gradient, and through the turbine before returning it to the stream. An underground power station is generally used at large facilities and makes use of
1425-455: A source of low-cost renewable energy. Alternatively, small hydro projects may be built in isolated areas that would be uneconomic to serve from a grid, or in areas where there is no national electrical distribution network. Since small hydro projects usually have minimal reservoirs and civil construction work, they are seen as having a relatively low environmental impact compared to large hydro. This decreased environmental impact depends strongly on
1520-414: A start-up time of the order of a few minutes. Although battery power is quicker its capacity is tiny compared to hydro. It takes less than 10 minutes to bring most hydro units from cold start-up to full load; this is quicker than nuclear and almost all fossil fuel power. Power generation can also be decreased quickly when there is a surplus power generation. Hence the limited capacity of hydropower units
1615-581: A total of 1,500 terawatt-hours (TWh) of electrical energy in one full cycle" which was "about 170 times more energy than the global fleet of pumped storage hydropower plants". Battery storage capacity is not expected to overtake pumped storage during the 2020s. When used as peak power to meet demand, hydroelectricity has a higher value than baseload power and a much higher value compared to intermittent energy sources such as wind and solar. Hydroelectric stations have long economic lives, with some plants still in service after 50–100 years. Operating labor cost
1710-452: Is hydroelectric power on a scale serving a small community or industrial plant. The definition of a small hydro project varies but a generating capacity of up to 10 megawatts (MW) is generally accepted as the upper limit. This may be stretched to 25 MW and 30 MW in Canada and the United States. Small hydro stations may be connected to conventional electrical distribution networks as
1805-635: Is also usually low, as plants are automated and have few personnel on site during normal operation. Where a dam serves multiple purposes, a hydroelectric station may be added with relatively low construction cost, providing a useful revenue stream to offset the costs of dam operation. It has been calculated that the sale of electricity from the Three Gorges Dam will cover the construction costs after 5 to 8 years of full generation. However, some data shows that in most countries large hydropower dams will be too costly and take too long to build to deliver
1900-531: Is connected via a dedicated 11/110 kV Ynd3 40 MVA transformer directly to the national grid via Transpower's Kawerau Substation. Hydroelectric power Hydroelectricity , or hydroelectric power , is electricity generated from hydropower (water power). Hydropower supplies 15% of the world's electricity , almost 4,210 TWh in 2023, which is more than all other renewable sources combined and also more than nuclear power . Hydropower can provide large amounts of low-carbon electricity on demand, making it
1995-470: Is highest in the winter when solar energy is at a minimum. Pico hydro is hydroelectric power generation of under 5 kW . It is useful in small, remote communities that require only a small amount of electricity. For example, the 1.1 kW Intermediate Technology Development Group Pico Hydro Project in Kenya supplies 57 homes with very small electric loads (e.g., a couple of lights and a phone charger, or
SECTION 20
#17327877109242090-445: Is initially produced during construction of the project, and some methane is given off annually by reservoirs, hydro has one of the lowest lifecycle greenhouse gas emissions for electricity generation. The low greenhouse gas impact of hydroelectricity is found especially in temperate climates . Greater greenhouse gas emission impacts are found in the tropical regions because the reservoirs of power stations in tropical regions produce
2185-642: Is located on the Rangitāiki River, just upstream of the village of Te Mahoe and approximately 29 km south of the town of Edgecumbe and some 37 km downstream of where the river mouth. This power station is the lower most of three hydro-electric facilities on the Rangitaiki River. The others being Aniwhenua Power Station and the Wheao and Flaxy Power Scheme. The embankment type Matahina Dam impounds Rangitaiki River approximately 37 km from
2280-462: Is not an energy source, and appears as a negative number in listings. Run-of-the-river hydroelectric stations are those with small or no reservoir capacity, so that only the water coming from upstream is available for generation at that moment, and any oversupply must pass unused. A constant supply of water from a lake or existing reservoir upstream is a significant advantage in choosing sites for run-of-the-river. A tidal power station makes use of
2375-452: Is not generally used to produce base power except for vacating the flood pool or meeting downstream needs. Instead, it can serve as backup for non-hydro generators. The major advantage of conventional hydroelectric dams with reservoirs is their ability to store water at low cost for dispatch later as high value clean electricity. In 2021, the IEA estimated that the "reservoirs of all existing conventional hydropower plants combined can store
2470-410: Is often higher (that is, closer to 1) with larger and more modern turbines. Annual electric energy production depends on the available water supply. In some installations, the water flow rate can vary by a factor of 10:1 over the course of a year. Hydropower is a flexible source of electricity since stations can be ramped up and down very quickly to adapt to changing energy demands. Hydro turbines have
2565-679: The Bonneville Dam in 1937 and being recognized by the Flood Control Act of 1936 as the premier federal flood control agency. Hydroelectric power stations continued to become larger throughout the 20th century. Hydropower was referred to as "white coal". Hoover Dam 's initial 1,345 MW power station was the world's largest hydroelectric power station in 1936; it was eclipsed by the 6,809 MW Grand Coulee Dam in 1942. The Itaipu Dam opened in 1984 in South America as
2660-549: The Industrial Revolution would drive development as well. In 1878, the world's first hydroelectric power scheme was developed at Cragside in Northumberland , England, by William Armstrong . It was used to power a single arc lamp in his art gallery. The old Schoelkopf Power Station No. 1 , US, near Niagara Falls , began to produce electricity in 1881. The first Edison hydroelectric power station,
2755-806: The International Exhibition of Hydropower and Tourism , with over one million visitors 1925. By 1920, when 40% of the power produced in the United States was hydroelectric, the Federal Power Act was enacted into law. The Act created the Federal Power Commission to regulate hydroelectric power stations on federal land and water. As the power stations became larger, their associated dams developed additional purposes, including flood control , irrigation and navigation . Federal funding became necessary for large-scale development, and federally owned corporations, such as
2850-633: The Tennessee Valley Authority (1933) and the Bonneville Power Administration (1937) were created. Additionally, the Bureau of Reclamation which had begun a series of western US irrigation projects in the early 20th century, was now constructing large hydroelectric projects such as the 1928 Hoover Dam . The United States Army Corps of Engineers was also involved in hydroelectric development, completing
2945-583: The Vulcan Street Plant , began operating September 30, 1882, in Appleton, Wisconsin , with an output of about 12.5 kilowatts. By 1886 there were 45 hydroelectric power stations in the United States and Canada; and by 1889 there were 200 in the United States alone. At the beginning of the 20th century, many small hydroelectric power stations were being constructed by commercial companies in mountains near metropolitan areas. Grenoble , France held
Matahina Power Station - Misplaced Pages Continue
3040-506: The potential energy of dammed water driving a water turbine and generator . The power extracted from the water depends on the volume and on the difference in height between the source and the water's outflow. This height difference is called the head . A large pipe (the " penstock ") delivers water from the reservoir to the turbine. This method produces electricity to supply high peak demands by moving water between reservoirs at different elevations. At times of low electrical demand,
3135-400: The water frame , and continuous production played a significant part in the development of the factory system, with modern employment practices. In the 1840s, hydraulic power networks were developed to generate and transmit hydro power to end users. By the late 19th century, the electrical generator was developed and could now be coupled with hydraulics. The growing demand arising from
3230-727: The Audit Department criticised the MOW's cooperative contract system and its method of reimbursing skilled tradesmen, the MOW introduced at Matahina a “daily project construction allowance”. However, the Public Service Commission refused to authorise the payment. The Cabinet refused the Commissioner of Works' argument that without the allowance it would be difficult to attract workers, as they believed these allowances would contribute to inflation and as well there
3325-463: The IEA released a main-case forecast of 141 GW generated by hydropower over 2022–2027, which is slightly lower than deployment achieved from 2017–2022. Because environmental permitting and construction times are long, they estimate hydropower potential will remain limited, with only an additional 40 GW deemed possible in the accelerated case. In 2021 the IEA said that major modernisation refurbishments are required. Most hydroelectric power comes from
3420-547: The MOW called tenders for the excavation and the driving of the diversion tunnel, which was 800 feet (240 m) long by 25 feet (7.6 m) diameter through a rock abutment on the west side of the river. The MOW had estimated that the work would cost £510,000, but the three lowest tenders were all under, that with the lowest being from the French company Etudes et Enterprises (£257,150), followed by Dominion Earthmovers and Morrison-Knudson/Downer/Ferguson. The MOW considered voiding
3515-609: The Power Planning Committee decided that Matahina was no longer urgent and could be delayed for two years, because of the priority that was being given to the HVDC Inter-Island link. Work began in 1960 on access roading and the construction of Te Mahoe village. As preliminary construction work began on site, detailed site investigations found that the site's geological conditions were more difficult than expected, with complicated ground faults, and that
3610-461: The Rangitaiki, causing a panicked spontaneous evacuation of people from the village of Te Mahoe and other settlements along the river. Although no abnormal leakage flows were observed, as a precaution in case the issues that had occurred during the original completion of the dam had reoccurred, a programme of performance monitoring and investigations was implemented. While no leakage was found in
3705-464: The ability to transport particles heavier than itself downstream. This has a negative effect on dams and subsequently their power stations, particularly those on rivers or within catchment areas with high siltation. Siltation can fill a reservoir and reduce its capacity to control floods along with causing additional horizontal pressure on the upstream portion of the dam. Eventually, some reservoirs can become full of sediment and useless or over-top during
3800-595: The balance between stream flow and power production. Micro hydro means hydroelectric power installations that typically produce up to 100 kW of power. These installations can provide power to an isolated home or small community, or are sometimes connected to electric power networks. There are many of these installations around the world, particularly in developing nations as they can provide an economical source of energy without purchase of fuel. Micro hydro systems complement photovoltaic solar energy systems because in many areas water flow, and thus available hydro power,
3895-519: The basis of stored water. The dam has crest length of 1,300 feet (400 m), is 1,200 feet (370 m) wide at its base and has a height of 86 metres (282 ft) above foundation level with a 76 metres (249 ft) head behind the dam. It has a core of 600,000 cu yd (460,000 m) of impermeable compacted weathered greywacke clay with hard ignimbrite rock shoulders. The dam abutments are hard rock underlain by compact alluvial materials at lower levels. The diversion and dewatering tunnels,
Matahina Power Station - Misplaced Pages Continue
3990-469: The course of these investigations when in December 1987, an erosion cavity developed in the crest surface above the damage near the west abutment. This was attributed to erosion of the surface subsidence, which had been noticeable for many years and which had previously been thought to have been caused by heavy traffic. This discovery resulted in the generation of electricity being stopped and drawing down of
4085-404: The daily rise and fall of ocean water due to tides; such sources are highly predictable, and if conditions permit construction of reservoirs, can also be dispatchable to generate power during high demand periods. Less common types of hydro schemes use water's kinetic energy or undammed sources such as undershot water wheels . Tidal power is viable in a relatively small number of locations around
4180-476: The dam and thus a calamitous failure. While the risk was considered small due to the very large mean recurrence interval of a Waiohau fault earthquake, the vulnerability of the dam to these earthquakes combined with the depth and volume of Lake Matahina made the hazard unacceptable to the Electricity Corporation of New Zealand (ECNZ). As a result, engineering work was commissioned to strengthen
4275-456: The dam in order to prevent a catastrophic release of the lake after a SEE and so to protect downstream populations and property, including that owned by the ECNZ. However, it was not expected that the dam could return to service without substantial reconstruction. The proposed strengthening was reviewed and endorsed by an International Review Board. It was decided to strengthen the dam by installing
4370-500: The dam is capable of passing the 20-year flood (500 cumecs) following a SEE without overtopping, even if the spillway was to be out of service. The lake had been lowered to about elevation 45 metres RL immediately after the dam's deficiencies had been identified in July 1996, and it was maintained at approximately this level throughout construction using the low-level outlet. The spillway gates were also kept open to manage any floods. Once
4465-435: The dam). This fault was considered to have generated four major earthquakes in the previous 11,800 years and has the potential for generating large surface fault displacements at the dam site. As part of this work, a Safety Evaluation Earthquake (SEE) was identified, with characteristics more intense than the mean of an expected Waiohau earthquake. The SEE was estimated to have a moment magnitude scale value of M W 7.2 with
4560-505: The dams, sometimes destroying biologically rich and productive lowland and riverine valley forests, marshland and grasslands. Damming interrupts the flow of rivers and can harm local ecosystems, and building large dams and reservoirs often involves displacing people and wildlife. The loss of land is often exacerbated by habitat fragmentation of surrounding areas caused by the reservoir. Hydroelectric projects can be disruptive to surrounding aquatic ecosystems both upstream and downstream of
4655-400: The design had been completed, Thiess Contractors undertook a $ 50 million contract to modify the dam, with completion in mid-1998. The strengthening works were organized so that dam could be capable, while the construction works were underway, of passing a 100-year flood with 3 m of freeboard and the 1,000-year flood without overtopping, with all spillway gates open. After deciding that Matahina
4750-427: The downstream shoulder and a maximum of 800 millimetres (31 in) in the upstream shoulder. Meanwhile, as a precaution and to facilitate inspection, the spillway gates were opened and the lake level was drawn down 2.5 metres (8.2 ft). This had not been done immediately following the earthquake, as electricity was not available to power the spillway gates from either from the station's local service system or from
4845-705: The effect of forest decay. Another disadvantage of hydroelectric dams is the need to relocate the people living where the reservoirs are planned. In 2000, the World Commission on Dams estimated that dams had physically displaced 40–80 million people worldwide. Because large conventional dammed-hydro facilities hold back large volumes of water, a failure due to poor construction, natural disasters or sabotage can be catastrophic to downriver settlements and infrastructure. During Typhoon Nina in 1975 Banqiao Dam in Southern China failed when more than
SECTION 50
#17327877109244940-399: The excess generation capacity is used to pump water into the higher reservoir, thus providing demand side response . When the demand becomes greater, water is released back into the lower reservoir through a turbine. In 2021 pumped-storage schemes provided almost 85% of the world's 190 GW of grid energy storage and improve the daily capacity factor of the generation system. Pumped storage
5035-400: The exterior upstream and downstream faces of the dam. As a result of issues with obtaining suitable materials for the earth dam, modifying the design to take account of the adverse site ground conditions and extensive grouting and installing additional drainage tunnels, filling of the lake was delayed. During the filling of the lake a large temporary increase in flow from the drainage blanket
5130-411: The external electrical lines. As a result, it took a few hours until the spillway gates could be opened. To those residents downstream who were unaware of the deliberate nature of this action, the increase in the river flow raised apprehension, lending weight to rumours of critical damage at the dam. Resulting fears of an imminent failure of the dam, spread through the population living along the banks of
5225-426: The following months, evidence of core cracking was discovered near the west abutment, similar to that which had occurred at the east abutment when the lake had first been filled. Investigations were unable to determine whether this damage had been due to the strain on the structure when it was first fill in 1967, or due to the 1987 earthquake, or to both. The lake had been operating below its normal operating level over
5320-534: The forest is inundated, substantial amounts of greenhouse gases may be emitted. Construction of a hydroelectric complex can have significant environmental impact, principally in loss of arable land and population displacement. They also disrupt the natural ecology of the river involved, affecting habitats and ecosystems, and siltation and erosion patterns. While dams can ameliorate the risks of flooding, dam failure can be catastrophic. In 2021, global installed hydropower electrical capacity reached almost 1,400 GW,
5415-506: The highest among all renewable energy technologies. Hydroelectricity plays a leading role in countries like Brazil, Norway and China. but there are geographical limits and environmental issues. Tidal power can be used in coastal regions. China added 24 GW in 2022, accounting for nearly three-quarters of global hydropower capacity additions. Europe added 2 GW, the largest amount for the region since 1990. Meanwhile, globally, hydropower generation increased by 70 TWh (up 2%) in 2022 and remains
5510-409: The lake are shallow (1 to 4 m), with a sinuous channel constricted by a narrow ignimbrite gorge. As the gorge widens down lake, the depth increases to15 metres (49 ft) along a delta front, and to 40 metres (130 ft) to 50 metres (160 ft) in the basin immediately behind the dam. As the Rangitaiki River has high water flow generation from the station tends to be 'run-of-river' rather than on
5605-564: The lake from the 2.5 metres (8.2 ft) below normal that it had been operating by a further 6 metres (20 ft) in order to allow repairs to be undertaken. While the dam was being repaired, the opportunity was taken to address the now identified latent flaws which had the potential to cause issues in the future, by making the following modifications to the core and transition zones and the core-foundation contacts at both abutments: These repairs and modifications lasted from December 1987 until mid-1988, and cost $ 16.5 million, of which $ 7 million
5700-519: The largest renewable energy source, surpassing all other technologies combined. Hydropower has been used since ancient times to grind flour and perform other tasks. In the late 18th century hydraulic power provided the energy source needed for the start of the Industrial Revolution . In the mid-1700s, French engineer Bernard Forest de Bélidor published Architecture Hydraulique , which described vertical- and horizontal-axis hydraulic machines, and in 1771 Richard Arkwright 's combination of water power ,
5795-750: The largest, producing 14 GW , but was surpassed in 2008 by the Three Gorges Dam in China at 22.5 GW . Hydroelectricity would eventually supply some countries, including Norway , Democratic Republic of the Congo , Paraguay and Brazil , with over 85% of their electricity. In 2021 the International Energy Agency (IEA) said that more efforts are needed to help limit climate change . Some countries have highly developed their hydropower potential and have very little room for growth: Switzerland produces 88% of its potential and Mexico 80%. In 2022,
SECTION 60
#17327877109245890-671: The last of the power stations on the Waitako River nearing completion and wishing to find work for itself and its large workforce, investigations were undertaken for four years in the late 1950s on the hydro-electric potential of the Bay of Plenty. As it held the most promise, the Kaituna River was the first to be considered for the development. However, the Kaituna proposal was abandoned after detailed investigations found that all of
5985-552: The lowest two, and giving the work to highest bidder as they were judged to be financially sounder and to have a workforce coming available, as they were completing Meremere Power Station. The MOW instead declined all offers and proposed to ask them to reprice with the performance bond increased from £20,000 to £100,000. Instead a revised price of £287,124 was accepted from Etudes et Enterprises. The company had undertaken work in Australia and in New Zealand to an acceptable standard, but
6080-432: The main tunnel. The company did a poor job of supporting the ground which caused cavities to be created outside of the required tunnel dimensions and therefore more back filling. They also did a poor job of excavating the overburden that covered the downstream portal area, which was 50% higher than stated in the contract and after it did a poor job of excavating the material, things were not helped by MOW being slow in clearing
6175-444: The material that was being used in the construction of the dam would require extensive grouting to control potential seepage, the MOW decided to install as a safety measure a dewatering tunnel to provide a means of partially lowering the water behind the dam, as well as a number of small drainage and grouting tunnels. Four tenderers were received from Fletcher Construction, Downers, Wilkins & Davies, Green & McCahill to undertake
6270-457: The mid-1950s the MOW was short of experienced investigating engineers and senior design staff which meant that without a full in-depth study, work on the scheme was started before Matahina was authorised under an Order in Council dated 14 January 1959. In 1959, the Power Planning Committee recommended approval of Matahina and this was given by the government later in that same year. The intention
6365-445: The pace of construction work began to increase due to the river having been diverted and the work-force doubling as resources were released from elsewhere. Work began on the dam foundations, which was made more complex as in a reversal of normal conditions, the rock was on top of the sediments. The river had removed all of the rock along the bottom of the gorge, and had deposited a mixture of boulders, gravels, pumice and other debris that
6460-633: The plant site. Generation of hydroelectric power changes the downstream river environment. Water exiting a turbine usually contains very little suspended sediment, which can lead to scouring of river beds and loss of riverbanks. The turbines also will kill large portions of the fauna passing through, for instance 70% of the eel passing a turbine will perish immediately. Since turbine gates are often opened intermittently, rapid or even daily fluctuations in river flow are observed. Drought and seasonal changes in rainfall can severely limit hydropower. Water may also be lost by evaporation. When water flows it has
6555-498: The possible sites on the river would be expensive to develop due to their geological complexity and would only be able to generate a small amount of electricity. Instead, a site on the northward flowing Rangitaiki River at the mouth of the Rangitaiki Gorge was selected, where the river had eroded through ignimbrite of andesitic composition to underlying tertiary age sediments of weak conglomerate, sandstone and siltstone. In
6650-726: The power station was delayed by two years, by which time the cost had doubled. Generator 1 was commissioned on 25 January 1967 and generator 2 in April 1967. In 1978, the New Zealand Department of Electricity which had been operating the power station since its commissioning was restructured into the Ministry of Energy. In 1987, the government established a state-owned enterprise called the Electricity Corporation of New Zealand (Electricorp) to take over
6745-450: The rainfall regime, could reduce total energy production by 7% annually by the end of the century. Lower positive impacts are found in the tropical regions. In lowland rainforest areas, where inundation of a part of the forest is necessary, it has been noted that the reservoirs of power plants produce substantial amounts of methane . This is due to plant material in flooded areas decaying in an anaerobic environment and forming methane,
6840-421: The required work. As Fletcher Construction was the lowest at £326,993, it was awarded the contract, and completed the work six months early and £676 below the original contract price. The intake and spillway structures were almost complete by 1963, and progress had been made on the powerhouse. By 1964, installation of the dam's foundations had been completed and the powerhouse was being prepared for installation of
6935-467: The river had worn through the solid ignimbrite rock in its bed, exposing loose gravel and rock. As well, there were pumice beds under the rock at one of the abutments. Because Matahina was some distance from the support facilities that had been built up at Mangakino to build the Waikato River stations this required the establishment of a substantial number of temporary facilities on site. After
7030-544: The river mouth to create the warm monomictic gorge-type Lake Matahina which is approximately 6 km in length with a surface area of 2.3 km, containing approximately 55,000,000 m of water. The lake and has an upstream catchment of 2,844 km which ranges in altitude from 150 metres (490 ft) to 1,300 metres (4,300 ft). The lake has a maximum depth of 50 metres (160 ft), a relative depth of 2.8%, and an annually fluctuating water level of only 0.5 metres (1.6 ft) to 0.75 metres (2.5 ft). Upper reaches of
7125-425: The spillway, the penstocks and powerhouse are located on a prominent rock spur which forms the west abutment. A grout curtain forms a partial cutoff within the spur supplemented by two drainage drives. The core material is constructed of weathered low plasticity gravelly clay greywacke, with transition zones on each face made of ignimbrite fines and softer quarry strippings. The transition zones are in turn protected on
7220-443: The trading operations of the Ministry of Energy. The power station was strongly shaken during the 1987 Edgecumbe earthquake . The instrument at the base of the dam recorded a M L 5.2 foreshock, the M L 6.3 main shock and the largest aftershock, a M L 5.5 event eight minutes after the main shock. The accelerometers on site also recorded that the dam had been subjected to a peak ground acceleration of 0.33 g at its base and in
7315-446: The trees in the area. Until it could obtain access to the downstream portal, and so undertake a full excavation, Etudes et Enterprises kept its tunnellers busy by widening the pilot drive. It made a claim on the MOW for the delay and was paid half of the amount and granted an extension of six months. By early 1962 most of the tunnel had been driven and it was more than half lined with concrete. Despite this extension, Etudies still completed
7410-438: The tunnel 15 months later and was awarded £25,611 of additional costs which meant that the overall contract price was still cheaper than the other tenderers. When the river was initially diverted through the diversion tunnel, the water scoured a large hole at the outlet of the tunnel. The cause was put down to hasty design. This required the construction of a stilling basin, which delayed full diversion by several months. In 1962
7505-627: The turbines. In that same year the workforce reached its peak of nearly 700. Beginning in September 1964 the dam's core was formed. By 1965 nearly 3,000,000 cu yd (2,300,000 m) of material had been installed, the powerhouse was almost complete, all concrete structures had been completed and progress had been made on installing the generating units. The dam was constructed with a sloping earth 600,000 cu yd (460,000 m) core flanked by inner and outer transition zones. Sandy clayey silt and silty clay derived from weathered greywacke
7600-547: The upstream and downstream faces of the dam by shoulders made of hard ignimbrite rockfill. Galatea Road runs across the top of the dam. From the dam two 16.5 feet (5.0 m) internal diameter penstocks direct water subjected to a 76-metre gross head to the Dominion Engineering Canada Francis 50,000 hp turbines located in the powerhouse which in turn which drive English-Electric salient pole synchronous 40 MW 11 kV generators. Each generator
7695-414: The upstream-downstream direction 0.43 g at the crest. A landslide generated by the earthquake into Lake Matahina from road works created a series of approximately one metre high waves, with reports that several of these waves overtopped the spillway gate. Power generation was interrupted when one generator was shut down by a shock-activated protective relay. Generation was resumed about 12 hours later, after
7790-527: The west abutment, was inferred to be the main trace of the fault. Although fault traces were exposed in the bottom of the core trench during construction, they were considered to be inactive at that time. During a reappraisal of the seismic risk at the site, which included trenching across the fault just south of the reservoir, evidence was found that there were four traces of the Waiohau fault (later revised to six by discoveries during subsequent strengthening of
7885-524: The world are hydroelectric power stations, with some hydroelectric facilities capable of generating more than double the installed capacities of the current largest nuclear power stations . Although no official definition exists for the capacity range of large hydroelectric power stations, facilities from over a few hundred megawatts are generally considered large hydroelectric facilities. Currently, only seven facilities over 10 GW ( 10,000 MW ) are in operation worldwide, see table below. Small hydro
7980-539: The world. The classification of hydropower plants starts with two top-level categories: The classification of a plant as an SHP or LHP is primarily based on its nameplate capacity , the threshold varies by the country, but in any case a plant with the capacity of 50 MW or more is considered an LHP. As an example, for China, SHP power is below 25 MW, for India - below 15 MW, most of Europe - below 10 MW. The SHP and LHP categories are further subdivided into many subcategories that are not mutually exclusive. For example,
8075-618: Was persona non grata on the Snowy Mountain because it had the habit of bidding low and then claiming excessive variations. They had also recently bid low for the contract to construct the Victoria Park motorway bridge in Auckland. Etudes et Enterprises commenced work on what was a planned 18 month long project by cutting a pilot tunnel at the top of the arch of proposed tunnel. This would provide ventilation while constructing
8170-512: Was a non-core asset due to its size and location away from the major river systems, Electricorp decided to sell it along with four other stations. The power station was sold to TrustPower in 1999 for $ 115 million. The civil structures were designed and constructed by the Ministry of Works, while the electrical plant was designed and installed by the New Zealand Electricity Department. The Matahina Power Station
8265-586: Was allowed to provide irrigation and power to citizens (in addition to aluminium power) after the war. In Suriname , the Brokopondo Reservoir was constructed to provide electricity for the Alcoa aluminium industry. New Zealand 's Manapouri Power Station was constructed to supply electricity to the aluminium smelter at Tiwai Point . Since hydroelectric dams do not use fuel, power generation does not produce carbon dioxide . While carbon dioxide
8360-438: Was estimated to be 1,000 imp gal (4,500 L), the engineers drilled 60 drainage 100 feet (30 m) deep wells below foundation level and filled them with gravel. As detailed site investigations were undertaken, it soon became clear that the site of the power station was next to an active earthquake faultline, offered poor foundations and the surrounding area lacked suitable material for an earth dam. As problems with
8455-424: Was observed, followed shortly afterwards by the finding of an erosion cavity downstream of the core in the east (right) abutment area. The lake was lowered and exploratory pits revealed that shear deformations induced by benches in the abutment had led to cracking of the core and inner transition of the dam. This needed extensive remedial work on the core, which combined with the previous delays meant that completion of
8550-539: Was plenty of employment available in the Bay of Plenty, especially at Kawerau. As a result, the Cabinet ordered that the projec to be closed down. However, the Commissioner gained the permission of the Minister of Works to undertake only a “slowing down”. This allowed excavation works to continue and all existing contracts to be completed. As a result, completion was expected to be delayed by 12 months. In February 1960,
8645-637: Was that the first electricity would be generated by April 1965, when there was expected to be a shortfall in generation capacity in the North Island. The estimated cost was £8 million. When the National Party was returned to power in 1960, they stopped work on the Maraetai II power station and ordered that its two turbines be allocated to Matahina. The use of these turbines required some redesign work, which slowed down construction. In 1961,
8740-505: Was the cost of improvements. The Waiohau fault (which is one of the faults of the North Island Shear Belt system) runs through the base of the dam, with the linear nature of the river valley south of the dam and the vertical offset of formation contacts across the valley attributed to the fault. During the original dam design studies in the early 1960s, an exposure in the ignimbrite ridge, 300 metres (980 ft) west of
8835-436: Was tunnelled through this material without the need for any excavation support. The faces of the inner transition were then covered with an outer transition constructed of a mix of the fine grades of hard ignimbrite, sandy gravel and gravelly silt. Lastly, rockfill formed hard ignimbrite blocks ranging in size from 150 metres (490 ft) to 900 metres (3,000 ft) were added and compacted by heavy tractor track rolling to form
8930-518: Was unsuitable for use as a foundation. Removal of this debris required excavation of a 1,000 feet (300 m) long by 160 feet (49 m) wide trench to a depth of 80 feet (24 m). A 20 feet (6.1 m) deep earthquake-resistant concrete cut-off wall was then constructed within it to control seepage. A specially imported machine was imported to make the concrete for this wall. It was a type of plastic concrete, designed to be pliable enough to withstand earthquakes. To further manage water seepage which
9025-412: Was used to form the core of the dam. It was placed dry of optimum to high densities. It was however stiff and susceptible to cracking under shear at low confining pressures and is also readily erodible. On each face of the core an inner transition was formed of unwelded ignimbrite, which was compacted to such a high density and had a high unconfined compressive strength that the subsequent inspection gallery
#923076