Mangorei Power Station facts for kids
Quick facts for kids Mangorei Power Station |
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 Location of Mangorei Power Station in New Zealand
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| Country | New Zealand |
| Location | Taranaki |
| Coordinates | 39°07′08.9″S 174°07′36.8″E / 39.119139°S 174.126889°E for the dam |
| Purpose | Power |
| Status | Operational |
| Construction began | 1904 |
| Opening date | 1906 |
| Owner(s) | New Plymouth Borough Council (1906 - 93) Taranaki Electricity (1993 - 1995) Powerco (1995 to 98) Trustpower (1998 -) |
| Operator(s) | Trustpower |
| Dam and spillways | |
| Type of dam | Concrete-core earth |
| Impounds | Mangamahoe Stream |
| Height (foundation) | 27.4 metres |
| Length | 160 metres |
| Reservoir | |
| Creates | Lake Mangamahoe |
| Power station | |
| Name | Mangorei Power Station |
| Coordinates | 39°06′18.5″S 174°07′07.7″E / 39.105139°S 174.118806°E |
| Operator(s) | Trustpower |
| Commission date | 1906 |
| Type | Conventional |
| Turbines | Four |
| Installed capacity | 4.5 MW (6,000 hp) |
| Annual generation | 20.9 GWh (75 TJ) |
| Website Trustpower |
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The Mangorei Power Station is a hydroelectric power plant located near Mangorei in Taranaki, New Zealand. It uses water from the Waiwhakaiho River and the Mangamahoe Stream to generate electricity. This station has been an important source of power for the local area for over a century.
History of Mangorei Power
Building the First Power Station
The idea for the Mangorei Power Station began with a design by an engineer named Mestayer. A contract to build the power scheme was signed on 13 July 1903. Workers started digging a tunnel for the water flow. They dug from different points, including a side tunnel and a deep shaft. To make sure the tunnel was straight, surveyors used special tools like plumb bobs and a theodolite.
The government gave permission for the power scheme to generate electricity on 24 February 1905. The entire project was finished by late 1905.
First Electricity in New Plymouth
The town of New Plymouth received its first electricity in January 1906. This new power lit up 120 street lamps and the town hall. By the end of that year, the power station was supplying electricity to 41 customers, running from dusk until midnight. Demand quickly grew, with 126 customers by 1907 and 230 by 1912.
The power station first had two turbines, each making 45 kilowatts (kW) of power. To meet the growing demand, the station was expanded. An additional 150 horsepower turbine, which made 90 kW of power, started working in December 1907.
Expanding the Power Supply
The original power station relied directly on the river's flow, meaning it didn't have a way to store water. This made it unreliable during dry summer periods when river levels were low. As New Plymouth grew and planned to introduce electric trams, more electricity and water were needed.
In 1909, the council hired engineer Henry Westcott Climie to find solutions. He suggested several ways to increase power. One idea was to build a new dam on the Mangamahoe Stream. This new diversion, completed in 1914, captured water from both the Waiwhakaiho River and the Mangamahoe Stream. It cost about £4,000.
With this increased water flow, the power station's total output grew to 750 kW. However, the new water intake often got blocked by stones and branches, which had to be cleared by hand. Improvements were made to its design and finished by January 1916.
Around the same time, two new 250 kW generators were added in 1912 and 1913. In 1914, the two original 45 kW generators were replaced with a new 250 kW generator. In 1915, the power system's voltage was updated, and again in 1921 to a three-phase system.
Damage to the Dam
On 25 March 1917, the Mangamahoe River bed was severely washed away under the tunnel. This caused the dam to lose all its water. A temporary dam was quickly built to get some water back.
Instead of repairing the old dam, which would have meant shutting down power to the town, it was decided to build a new dam. This new dam would be about 15 metres downstream from the damaged one. The design for a new concrete dam was approved in May 1917.
The new dam was 33 metres long at the top and 5.5 metres high. It was built with a strong base. Workers had to dig deeper than planned to find a solid, watertight foundation. A large valve was installed to allow the lake to be emptied and to remove sand. By February 1918, the new dam was finished and refilled with water.
Planning for More Power
As the demand for electricity in New Plymouth kept rising, the council decided to expand the Mangorei scheme even further. In late 1918, they hired engineer John Blair Mason to explore options. Mason proposed several plans, with "Scheme D" becoming the preferred choice.
Scheme D involved building a new, much taller dam (about 33.5 metres high) on the Mangamahoe Stream. This would create a larger lake, covering about 12 hectares, and provide a lot more stored water. This bigger lake would allow the power station to generate much more power. The estimated cost for this large project was £46,000.
Over the next two years, the plans were changed. Scheme D was renamed Scheme 1. It would create an even larger lake, covering 38 hectares, and require two long embankments to prevent water from overflowing. This scheme was expected to produce 9,000 horsepower.
The council decided in 1919 to go ahead with a smaller version of the plan, called the "partial scheme." However, by January 1920, the estimated cost had jumped to £112,000. Despite the high cost, the town's residents approved loans to fund the project. By October 1920, the cost increased again to £172,000, and the council had to ask for another loan.
The Partial Scheme is Completed
The partial scheme was finished in early 1923. It included a new concrete weir and water intake on the Waiwhakaiho River, located about 2.4 kilometres upstream from the old one. This new intake had gates to control the water flow.
From the intake, water flowed through a 548-metre-long tunnel called Tunnel No. 1. Workers used pony-drawn trucks to remove the excavated material. The tunnel was lit by electricity and had air shafts for ventilation.
At the end of Tunnel No. 1, a 11-metre-high "Turning Wall" dam was built to direct water into Water Race No. 1. This 340-metre-long race led to a 170-metre-long pipeline that carried water over the Mangamahoe Stream. The water then entered Water Race No. 2, which was 600 metres long. This race then connected to Tunnel No. 2, a 1,219-metre-long tunnel that led to a forebay (a small reservoir before the power station). From here, steel pipes called penstocks carried the water down to the powerhouse.
This improved water supply and increased water pressure allowed the council to install two new 1,000 kVA generators. They also upgraded one existing 250 kW machine to produce 750 kVA and replaced another 250 kW unit with a new 1,000 kVA unit.
Problems were found in Tunnel No. 2, which led the council to dismiss their consulting engineers in 1923. In April 1928, a landslide destroyed part of the pipeline over the Mangamahoe Stream, cutting off water to the power station for about two weeks. During this time, street lights and trams were turned off, and New Plymouth relied on power from another source.
Creating Lake Mangamahoe
As electricity demand continued to grow, the council decided to build the full scheme, including a large dam on the Mangamahoe Stream. This would create a bigger reservoir for both power generation and a reliable water supply for New Plymouth. The contract to build the dam was awarded in March 1929.
Construction began in 1929. The stream was diverted through a tunnel, and the dam's foundations were dug. Tractors and scrapers, which were new at the time, were used to build the dam.
When the dam was finished in 1931, it created Lake Mangamahoe, covering about 32 hectares of land. At the time, this dam was the highest earth dam in Australia and New Zealand. The existing water races and pipeline were left in place and became submerged by the new lake.
By March 1948, the power station had an output of 3,750 kW, thanks to various upgrades and new generators. On 1 September 1983, the power station was recognized as a Historic Place Category 2 in New Zealand.
Changes in Ownership
In the early 1990s, New Zealand's electricity industry was reorganized. The electricity department of the New Plymouth City Council joined with the Taranaki Electric Power Board in 1993 to form Taranaki Energy Ltd.
In 1995, Taranaki Energy Ltd merged with and became Powerco. Later, in 1998, a new law required electricity companies to separate their network (power lines) and retail (selling electricity) businesses. Powerco chose to focus on networks and sold its five power stations, including Mangorei, to Trustpower.
Recent Improvements
In recent years, Trustpower has worked to improve the tunnels that supply water to the power station. They have made the tunnel linings smoother to reduce friction, which helps the water flow more efficiently.
How Mangorei Power Station Works
Design and Water Flow
The Mangorei Power Station uses a clever design to generate electricity. First, a weir (a small dam) on the Waiwhakaiho River diverts water into a concrete-lined tunnel called Tunnel No. 1. This tunnel is 548 metres long and 2.2 metres in diameter. It carries the water to the top of Lake Mangamahoe.
Lake Mangamahoe is a man-made lake created by a large earth dam at its northern end. This dam holds back the Mangamahoe Stream. The dam is 27.4 metres high and 160 metres long at the top. It has a strong concrete core running through its centre. The side of the dam facing the lake is covered with stone to protect it.
On the western side of the lake, there's an intake structure with four gates that can be controlled remotely. From this structure, Tunnel No. 2, which is 1,219 metres long and 2.2 metres in diameter, carries water from the lake to a forebay (a large chamber) that is 11.2 metres in diameter. From the forebay, two large steel pipes called penstocks carry the water downhill to the powerhouse.
Inside the powerhouse, there are four generators: one 700 kW generator and three 1.3 MW generators. After the water passes through the generators, it flows into a tailrace (a channel) that empties into the Waiwhakaiho River, about six kilometres downstream from where it was first diverted.
Water is also taken from two intakes on the lake's western shore to a nearby water treatment plant. This water is then cleaned and sent to homes and businesses in the New Plymouth area.
Operating the Power Station
Water Management
The Mangorei Power Station operates under special permissions, called resource consents, which were granted in 1996 and are valid until June 2021. These consents allow the power station to divert up to 10 cubic metres of water per second from the Waiwhakaiho River and then return it to the river. The power station must also make sure that a certain amount of water always flows in the river below the diversion weir.
Lake Mangamahoe is important not only for generating electricity but also as a source of drinking water for New Plymouth. It is also a Wildlife Refuge, protecting local animals. To help longfin eels migrate, a special program catches them and moves them safely past the power station.
The Mangorei Power Station is connected to Powerco's electricity network. It is operated remotely using a special computer system called SCADA from Trustpower's control centre in Tauranga.
