Motukawa Power Station facts for kids
Quick facts for kids Motukawa Power Station |
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 Location of Motukawa Power Station in New Zealand
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| Country | New Zealand |
| Location | Taranaki |
| Coordinates | 39°12′31.9″S 174°20′0.3″E / 39.208861°S 174.333417°E for the dam on the Mako Stream |
| Purpose | Power |
| Status | Operational |
| Construction began | 1923 |
| Opening date | 1927 |
| Owner(s) | Taranaki Electric Power Board (1927 - 1993) Taranaki Electricity (1993 - 95 ) Powerco (1995 - 98) Trustpower (1998 - ) |
| Operator(s) | Trustpower |
| Dam and spillways | |
| Type of dam | Earth |
| Impounds | Mako Stream |
| Height (foundation) | 15 m |
| Reservoir | |
| Creates | Lake Ratapiko |
| Surface area | 21 hectare |
| Maximum length | 3 km |
| Power station | |
| Name | Motukawa Power Station |
| Coordinates | 39°11′2.3″S 174°22′54.0″E / 39.183972°S 174.381667°E |
| Operator(s) | Trustpower |
| Commission date | 1927 |
| Type | Conventional |
| Hydraulic head | 99 m |
| Turbines | Four |
| Installed capacity | 5 MW (6,700 hp) |
| Annual generation | 22 GWh (79 TJ) |
| Website Trustpower |
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The Motukawa Power Station is a hydroelectric power plant in Taranaki, New Zealand. It uses water from the Manganui River and Waitara River areas to make electricity. Water is taken from a small dam (called a weir) on the Manganui River near Tariki. This water then flows through a special channel to Lake Ratapiko. From the lake, it goes through large pipes called penstocks to the power station. The water then flows out into the Mākara Stream, which is part of the Waitara River.
Contents
History of Motukawa Power Station
Building the Power Station
Work on the Motukawa Power Station began in 1923.
The first step was to build a weir (a small dam) on the Manganui River near Tariki in 1924. This weir helped power a small generator. This generator provided electricity for building the main power station. It even supplied power to some local farmers!
To help with construction, a 200 kVA hydro generator was set up in 1924. It had enough extra power to give electricity to nearby farms. You can still see parts of this old generator today.
The plan was to move water across a swampy area at Ratapiko using a canal and a tunnel. But digging through mud, peat, and buried logs was very hard. The tunnel kept collapsing.
Because of these problems, they decided to build a canal instead of a tunnel for most of the route. Two workers used a powerful pump to clear the swampy soil and explosives to remove buried trees.
For another part of the tunnel, they bought a special tunnelling machine from Scotland. It arrived in New Zealand in January 1924. This was probably the first time such a machine was used in New Zealand!
Setting up the machine was difficult, and they even received the wrong parts. New parts had to be made in New Zealand.
The machine finally started digging on September 15, 1924. It dug through hard rock (called papa rock) about one meter per hour. But they kept hitting large boulders, which had to be dug out by hand. One boulder was over 7 meters long!
In November 1925, after digging 2,080 meters, the ground changed to soft, silty swamp. The tunnel collapsed over the machine, filling 80 meters of the tunnel. Luckily, no one was hurt. They had to dig a large crater from above to get the machine out.
Workers then finished the tunnel by hand, using strong timber supports. By May 1926, the damaged part of the tunnel was lined with concrete. The rock sections were lined with a spray-on concrete called shotcrete. The tunnel was finally finished on August 23, 1926.
The tunnelling machine was removed in May 1926. It was later used for parts for other projects.
The whole project ended up costing more than twice the original estimate. Because of this, the power board had to charge extra fees to customers living near the power lines for four years to help cover the costs.
Starting Operations
The first generator at Motukawa Power Station began making electricity on January 9, 1927. The last of the three main generators started working in 1938.
Stratford received electricity from Motukawa by 1930. Inglewood got its supply by 1933, and Waitara by 1934.
Upgrades in the 1970s
In 1970, the station was upgraded to make more power. The old steel pipe (penstock) that carried water was replaced with a larger, stronger one. The original designers had planned for this, so the change was made with very little interruption to the electricity supply.
Changes in Ownership
In the early 1990s, New Zealand's electricity companies changed how they operated. The Taranaki Electric Power Board joined with New Plymouth Energy in 1993 to form Taranaki Energy Ltd.
In 1995, Taranaki Energy Ltd merged with Powerco.
In 1998, a new law required electricity companies to separate their power lines from their power stations. Powerco decided to focus on power lines. So, they sold their five power stations, including Motukawa, to Trustpower. Trustpower still owns and runs the station today.
Recent Improvements
In 2005, Trustpower added a new weir and a small 200 kW generator in the canal. This generator uses the natural drop in the canal to make extra power. In 2007, pumps were installed to lift water from the Mangaotea Stream into the canal. These improvements have helped the Motukawa scheme produce even more electricity.
How Motukawa Power Station Works
The Motukawa scheme uses a 99-meter drop in elevation between the Manganui River and the Waitara River. This drop helps drive three generators inside the power station. There's also a smaller generator in the canal.
Water Collection (Headworks)
Water is taken from the upper part of the Manganui River using a weir (a low dam). This weir has a special fish pass to help fish move past it. It's located about four kilometers from the main road.
Up to 5,200 liters of water per second can be taken from the river. Two motorized gates control how much water flows from the weir into a short canal and then into a settling pond. From this pond, the water travels along a five-kilometer canal. This canal includes two tunnels and a bridge (aqueduct) over the Mangaotea Stream before it reaches Lake Ratapiko.
Rules say that at least 400 liters of water per second must stay in the Manganui River below the weir. This ensures fish can pass and the river stays healthy.
Lake Ratapiko
The canal flows into Lake Ratapiko. This is a man-made lake created by building a 15-metre-high (49 ft) earth dam across the Mako Stream. The lake is 21 hectares (about 210,000 square meters) in size and about three kilometers long. It's quite shallow, with an average depth of 2.5 meters.
The lake's water level can only change by one meter when the power station is making electricity. Besides storing water for the power station, Lake Ratapiko is also used for fun activities like power boat racing and water skiing!
The Tunnel and Pipes
From Lake Ratapiko, water flows into a special structure called a forebay. Then it enters a 2,875-kilometre-long (1,786 mi), 2.13-metre-diameter (7.0 ft) tunnel. This tunnel carries the water to a large chamber called a surge chamber, located in the hill above the power station.
From the surge chamber, a 1.6-metre-diameter (5.2 ft) steel pipe (penstock) takes the water down to the powerhouse. The powerhouse is found on Motukawa Road in Ratapiko, Inglewood.
After the water has passed through the generators in the power station, it flows out into the Mākara Stream, which is a branch of the Waitara River.
Operating the Power Station
The Motukawa Power Station operates under 23 special permits (resource consents) with 186 conditions. These permits were obtained in 2001 and will expire in June 2022.
Eels and fish cannot pass through the power scheme on their own. However, there's a successful program to trap and move longfin eels. This helps these eels migrate (travel) safely.
The power station is connected to Powerco's electricity network.
The Motukawa Power Station is controlled remotely. This means people at Trustpower's control center in Tauranga can operate it using a special computer system called SCADA.
