Roxburgh Dam facts for kids
Quick facts for kids Roxburgh Dam |
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Roxburgh Dam machine hall
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 Location of Roxburgh Dam in New Zealand
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| Location | Central Otago, New Zealand |
| Coordinates | 45°28′33″S 169°19′21″E / 45.475811°S 169.322555°E |
| Construction began | 1949 |
| Opening date | 3 November 1956 |
| Construction cost | NZ£24,102,800 |
| Owner(s) | Contact Energy |
| Dam and spillways | |
| Type of dam | Concrete gravity dam |
| Impounds | Clutha River / Mata-Au |
| Height | 76 m (249 ft) |
| Length | 358 m (1,175 ft) |
| Width (crest) | 10.7 m (35 ft) |
| Width (base) | 61 m (200 ft) |
| Spillway capacity | 4,248 m3/s (150,000 cu ft/s) |
| Reservoir | |
| Creates | Lake Roxburgh |
| Surface area | 6 km2 (2.3 sq mi) |
| Normal elevation | 132 m |
| Power station | |
| Operator(s) | Contact Energy |
| Commission date | 1956 − 1962 |
| Turbines | 8 |
| Installed capacity | 320 MW (430,000 hp) |
| Annual generation | 1,650 GWh (5,900 TJ) |
The Roxburgh Dam is one of the first large hydroelectric power stations built in the lower part of New Zealand's South Island. It stretches across the Clutha River / Mata-Au. The dam is about 160 kilometres (99 mi) from Dunedin and 9 kilometres (5.6 mi) north of the town of Roxburgh. A small community called Lake Roxburgh Village is located near the dam's western side.
Contents
Building the Roxburgh Dam
Early Construction Work
Starting the Project
The Ministry of Works (MOW) was a government group in charge of designing and building power stations in New Zealand. In July 1949, they started digging a special channel to divert the river. This channel was planned to be about 610 m (2,000 ft) long, 30 m (98 ft) wide, and 21 m (69 ft) deep. They had to remove a huge amount of earth and rock for this. By the end of 1950, about 720 people were working on the site.
A Village for Workers
To house all the workers, the Ministry of Works built a special village. In 1947, they started with a camp for single men. By 1950, they began building 100 cottages for families. The next year, they added a YMCA hall, shops, a hospital, and 225 more cottages.
Eventually, the village grew to 724 houses. It also had a hostel, a primary school for 600 children, a cinema, shops, churches, and sports courts. There were also four camps for single men with 1000 huts. These facilities cost a lot of money, about NZ£2.2 million. The government even built a temporary power station to supply electricity to the village and the construction site.
Moving Materials and Equipment
Transporting heavy materials to the dam site was a big challenge. The main railway line to Roxburgh had steep hills and tight curves, which limited how much could be carried. It also had tunnels that were too small for the largest parts of the power station.
So, they used different routes. Most building materials went by train to Roxburgh, then by road to the dam. For very large items, like the turbine runners, they used a different railway line that had no small tunnels. These huge parts were then moved by a special transporter truck from the train station to the dam.
The roads near the site were also improved, and a new bridge was built over the Teviot River. A temporary Bailey bridge was put across the Clutha River in 1949 to help with access. Timber for the project came from a mill at Tapanui, transported by train. At its busiest, 15,000 to 20,000 feet of timber were moved daily.
Huge silos were built at the Roxburgh railway station to store cement. At its peak, the project used 50,000 tons of cement a year!
Challenges and Changes
Seeking Help from Overseas
The Ministry of Works realized they didn't have enough engineers and staff to build all the power stations the government wanted. A British group offered to design and build Roxburgh Dam. However, the New Zealand government had concerns about the cost and giving one company too much control. So, they said no to the offer.
Work continued slowly on the site. The river diversion channel was taking longer than planned.
Calling for Contractors
In 1949, a new government came into power. They preferred private companies to do big projects. By 1951, delays at Roxburgh Dam were causing worries about power shortages. The Minister of Works, Stan Goosman, decided to ask private companies to bid on building the dam.
Eight companies sent in their bids. The lowest bid came from a British company called Holland, Hannen & Cubitts. After more talks, this company teamed up with a Swiss company, S A Conrad Zschokke. They signed a contract in July 1952. The contract included bonuses for finishing early and penalties for being late.
The Ministry of Works built two cableways to carry concrete. They also bought a concrete mixing plant that had been used to rebuild Pearl Harbor after World War II. This plant started working in April 1953.
The new group of contractors brought 82 engineers and supervisors and 322 workers from overseas. They took over the civil construction work from the Ministry of Works in September 1952.
Growing Concerns
By March 1953, the Ministry of Works was worried about the contractors' progress. They felt the management team lacked experience in building hydro power stations. Many of the new workers were immigrants with little construction experience and limited English, which also slowed things down.
By October 1953, it was clear the dam would not be ready on time. The contractors changed some of their senior staff. Workers were also unhappy about changes to their working hours and pay.
Downer & Co Takes Over
Because of power shortages in the South Island, the government decided to make a big change. In April 1954, they asked a major New Zealand construction company, Downer & Co, to join the project. The original contract was cancelled, and a new one was signed with a group now called Cubitts Zschokke Downer. Arnold Downer from Downer & Co took charge of all the work on site. The new plan aimed to finish the dam by late 1956.
Diverting the River and Building the Dam
River Diversion
A key step was to block the Clutha River so all its water flowed through the new diversion channel. This was a difficult task because the river's flow was high. Arnold Downer decided to go ahead despite the challenging conditions. On July 1, 1954, twelve bulldozers worked for twelve hours, moving huge amounts of earth and rocks. They successfully diverted the river into the channel.
Once the river was diverted, temporary dams called cofferdams were built upstream and downstream of the main dam site. The area between them was then pumped dry. People hoped to find gold in the exposed riverbed, but they were disappointed.
Workers then started digging the foundations for the main dam. They found a large gravel-filled hole in the riverbed, which they dug out and filled with special concrete.
Under Arnold Downer's leadership, the construction sped up. The amount of concrete poured each week increased quickly. By May 1955, the project was on track, with the powerhouse construction six months ahead of schedule.
How the Dam was Built
The Roxburgh Dam was built using large concrete blocks, each about 15 m (49 ft) wide. There were small gaps between these blocks, which were filled later. Different concrete mixes and cooling pipes were used to control the temperature of the concrete. This was important to prevent cracks, which could weaken the dam.
A special "grout curtain" was also installed under the dam to make the rock stronger and prevent water leaks. In total, about 535,000 m3 (18,900,000 cu ft) of concrete were used to build the dam and spillway. Most of the cement came from a factory near Dunedin.
A company called Stevenson & Cook made and installed the huge steel pipes (penstocks) that carry water to the turbines. They also built the steel frame of the powerhouse.
Electrical Equipment and Power Lines
Installing the Generators
The government's State Hydro-electric Department was in charge of buying and installing all the electrical equipment. They started installing the first generating unit in August 1954.
In November 1955, a problem was found with the wiring in the generators. Luckily, workers went on strike for a few weeks, which gave engineers time to fix all the wiring.
Building Power Lines
To connect the new power station to cities, new transmission lines were built. A 110 kV line was built to Gore. Then, a longer 110 kV line was built to Halfway Bush substation in Dunedin, finishing in July 1955.
The main connection was a very long 220 kV line, about 428-kilometre ([convert: unknown unit]), built from Roxburgh to a new substation near Christchurch. This line was completed by the winter of 1956 and cost about £1 million.
Filling the Lake and Opening the Dam
Lake Filling Begins
By June 1956, there were power cuts across the South Island because of electricity shortages. The government urged workers to finish quickly so the lake could be filled. They even offered a bonus to the workers if the lake was filled before August 19.
At midnight on July 21, 1956, the lake began to fill. The water level rose quickly, about 0.9 m (2 ft 11 in) an hour. As the lake filled, engineers noticed leaks behind the dam's grout curtain. They had to stop filling the lake temporarily to fix this problem by adding more grout.
First Power Generated
Despite the leak, the need for electricity was urgent. On July 23, 1956, the lake reached the top of the spillway. The first generating unit was immediately tested and connected to the national power grid at 6 p.m. The next day, the second unit was also ready. This allowed the 220 kV line to Christchurch to start working.
The third generating unit was ready in August 1956, and the fourth in December 1956. The Roxburgh Power Station was officially opened on November 3, 1956. The remaining four generating units were installed between 1959 and 1962.
With Roxburgh Dam running, power cuts in the South Island ended, and there was plenty of electricity for many years.
Project Costs
In 1947, the project was expected to cost £11.5 million. By 1949, this estimate grew to £17 million. The final cost of the entire project was £24,102,800. This included money for building the dam, buying and installing the generators, and other works.
How the Dam Works Today
Upgrades and Ownership
Over the years, the Roxburgh Dam has been updated. In the 1990s, its control systems were automated, meaning it could run without people constantly on site. Now, it's controlled from the Clyde Power Station.
In 1987, the dam became part of a new company called Electricity Corporation of New Zealand (ECNZ). Then, in 1996, ownership was transferred to Contact Energy, which later became a private company.
Generator Improvements
The generators at Roxburgh Dam sometimes ran hotter than ideal. Engineers found ways to improve the airflow and cooling inside the generators. Starting in 2002, all the generating units underwent a major upgrade. This included installing new parts, improving the turbines, and replacing cooling systems. These changes helped the generators work more efficiently.
Fire Safety
To improve fire safety, the powerhouse was divided into separate fire zones in the mid-1990s. Fire-rated doors and walls were installed to stop fire or smoke from spreading. However, these changes also reduced airflow, making the machine hall hotter. To fix this, new systems were put in place that automatically close fire doors if an alarm goes off, but keep them open otherwise to allow air to circulate.
Power Boost
In 2012, a key transformer was replaced with a much more powerful one. This change removed a limit on how much power the station could send out, allowing it to generate more electricity.
Design of the Roxburgh Dam
The Roxburgh Dam is a concrete gravity dam, meaning it uses its own weight to hold back the water. It is about 357-metre ([convert: unknown unit]) and 56-metre ([convert: unknown unit]). Eight large steel pipes, called penstocks, carry water from the dam to the powerhouse below.
The dam has three huge spillway gates on its western side. These gates can release large amounts of water, designed to handle very big floods. Below the spillway, there were also three low-level sluice gates. These were used to divert the river during construction. Now, one of these gates has been sealed with concrete.
The Powerhouse Building
The powerhouse is where the electricity is made. It's built with a steel frame and concrete panels. Inside, two large cranes can move heavy equipment.
The main machinery is on three different floors. The building was designed to be watertight up to a certain flood level. The windows are high up, and the doors are raised. The generator transformers, which change the electricity's voltage, are located outside on a platform above the river's outflow.
Generating Electricity
Each of the eight penstocks feeds water to a Francis turbine. These turbines spin at a speed of 136.4 revolutions per minute. Each turbine can produce 56,000 horsepower and uses a lot of water when running at full power.
Each turbine is connected to a large generator. These generators produce electricity at 11,000 volts. They are air-cooled by fans, and water-cooled radiators help remove heat.
The electricity from the generators goes to large transformers. These transformers can change the voltage to either 110,000 volts or 220,000 volts. The power then travels through overhead lines to an outdoor switchyard.
Backup Power
The power station has two smaller auxiliary generating units. These provide backup power for the station's own needs. They are supplied by a separate penstock from the top of the dam. These units were upgraded in 2017.
Lake Roxburgh
Lake Roxburgh is the lake formed behind the dam. It stretches for almost 30 kilometres (19 mi) upstream towards the town of Alexandra.
How the Dam is Operated
The Roxburgh Dam must follow certain rules about how much water it releases. These rules are set by resource consents that last until 2042. The dam must always release at least 250 m3/s (8,800 cu ft/s) of water.
Since the dam was built, sediment (like sand and gravel) that used to flow down the Clutha River has been trapped behind the dam. This has caused the riverbed downstream to rise. Floods have also caused problems in Alexandra. To help with this, Contact Energy, the dam's owner, sometimes lowers the lake level during floods to try and flush sediment downstream.
The maximum operating level of Lake Roxburgh was increased slightly in 2009. This allows the power station to generate more electricity. However, there are conditions to ensure that the dam's operations match natural flood flows and protect local areas.
Since 2012, a program has been in place to help eels (called elvers) get around the dam. They are trapped below the dam and then transported to the lake above it.
Images for kids
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Spillway
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Outdoor view, clearly showing the eight penstocks
