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Maraetai Power Station
Maraetai Power Station is a hydroelectric power station on the Waikato River, in the North Island of New Zealand. It is the fifth of the eight hydroelectric power stations on the Waikato River, and at 360 MW, is the largest hydroelectric station on the Waikato.
The station has two powerhouses - Maraetai I powerhouse is directly in front of the Maraetai Dam, while Maraetai II powerhouse is located 550 metres (1,800 ft) downstream of Maraetai I. Although both are completely separate, both powerhouses are operated as one power station.
Maraetai is owned and operated by Mercury Energy.
In early 1946, the Minister of Public Works Bob Semple, announced a full development of the Waikato River, with the first three stations planned at Ohakuri, Whakamaru, and Maraetai. Although Ohakuri was chosen first, the choice soon shifted to Whakamaru as it would be the best location for transmission needs. However, more investigation had been done for the Maraetai site, and starting Whakamaru first would make it more complex to divert the river for Maraetai later, so it was decided to build Maraetai first.
Investigations into a hydroelectric station at Maraetai had been completed between 1940 and 1945. The site was in a deep narrow gorge, west of Tokoroa and 20 miles (32 km) upstream of Arapuni. Because of the narrowness of the gorge, the powerhouse took up the entire length of the base of the dam, meaning no orthodox spillway could be constructed. This meant that the spillway had to be designed as part of the diversion tunnel. The site was composed of volcanic ignimbrite, which had cracked extensively on cooling meaning extensive grouting of the rock was required.
Construction of Maraetai I began in 1946, with the construction of an access road from Tokoroa, and establishing services and accommodation for the workers of the dam. The service and accommodation camp formed the town of Mangakino, on the south shore of what would become Lake Maraetai. Problems were encountered right from the beginning - the Second World War had just ended, which meant there was a great deal of shortages of labour and materials. The Public Works department's work-force was less than two-thirds of its pre-war size, with thousands of vacancies not filled. Concrete and steel were also in short supply, as steel imports were less than half their pre-war levels, and local contractors could only produce two-thirds of the required amount of concrete. Combined with industrial unrest and the nature of the site, the target completion date of 1951 became less achievable.
Work on the diversion tunnel - 25 feet (7.6 m) in diameter and 1,685 feet (514 m) in length - began in late 1946 on the southern side of the site. However, work was slowed by large amounts of water that poured into the tunnel until it was extensively grouted with cement and bitumen and lined with concrete. Because of the constant water seepage, it was not uncommon for the workers to work in knee-high or even waist-high water. By 1948, some 800 workers were working on the site. The tunnel was completed in March 1949, when the northern portal was opened and the first water flowed through the tunnel. Work then started by building cofferdams to block the natural channel of the river and allow dam construction to begin. The Taupō control gates were shut to lower the water level in the Waikato, and 11 bulldozers frantically pushed spoil into the river to stop the natural flow. The process was hampered by unexpected heavy rain which caused the river to rapidly rise, with it taking 27 hours to finally dam the river's natural course. The spillway tunnel was then constructed, which dropped at a 45-degree angle to intersect with the diversion tunnel.
In late 1949, work finally started on the dam foundations. Extensive and careful grouting of the rock took place, reaching 200 feet (61 m) below the river bed, and along the sides for a length of 1,000 feet (300 m). The grouting involved drilling thousands of holes in the rock face, and 11,000 tonnes (11,000 long tons; 12,000 short tons) of cement was used in the process.
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Maraetai Power Station
Maraetai Power Station is a hydroelectric power station on the Waikato River, in the North Island of New Zealand. It is the fifth of the eight hydroelectric power stations on the Waikato River, and at 360 MW, is the largest hydroelectric station on the Waikato.
The station has two powerhouses - Maraetai I powerhouse is directly in front of the Maraetai Dam, while Maraetai II powerhouse is located 550 metres (1,800 ft) downstream of Maraetai I. Although both are completely separate, both powerhouses are operated as one power station.
Maraetai is owned and operated by Mercury Energy.
In early 1946, the Minister of Public Works Bob Semple, announced a full development of the Waikato River, with the first three stations planned at Ohakuri, Whakamaru, and Maraetai. Although Ohakuri was chosen first, the choice soon shifted to Whakamaru as it would be the best location for transmission needs. However, more investigation had been done for the Maraetai site, and starting Whakamaru first would make it more complex to divert the river for Maraetai later, so it was decided to build Maraetai first.
Investigations into a hydroelectric station at Maraetai had been completed between 1940 and 1945. The site was in a deep narrow gorge, west of Tokoroa and 20 miles (32 km) upstream of Arapuni. Because of the narrowness of the gorge, the powerhouse took up the entire length of the base of the dam, meaning no orthodox spillway could be constructed. This meant that the spillway had to be designed as part of the diversion tunnel. The site was composed of volcanic ignimbrite, which had cracked extensively on cooling meaning extensive grouting of the rock was required.
Construction of Maraetai I began in 1946, with the construction of an access road from Tokoroa, and establishing services and accommodation for the workers of the dam. The service and accommodation camp formed the town of Mangakino, on the south shore of what would become Lake Maraetai. Problems were encountered right from the beginning - the Second World War had just ended, which meant there was a great deal of shortages of labour and materials. The Public Works department's work-force was less than two-thirds of its pre-war size, with thousands of vacancies not filled. Concrete and steel were also in short supply, as steel imports were less than half their pre-war levels, and local contractors could only produce two-thirds of the required amount of concrete. Combined with industrial unrest and the nature of the site, the target completion date of 1951 became less achievable.
Work on the diversion tunnel - 25 feet (7.6 m) in diameter and 1,685 feet (514 m) in length - began in late 1946 on the southern side of the site. However, work was slowed by large amounts of water that poured into the tunnel until it was extensively grouted with cement and bitumen and lined with concrete. Because of the constant water seepage, it was not uncommon for the workers to work in knee-high or even waist-high water. By 1948, some 800 workers were working on the site. The tunnel was completed in March 1949, when the northern portal was opened and the first water flowed through the tunnel. Work then started by building cofferdams to block the natural channel of the river and allow dam construction to begin. The Taupō control gates were shut to lower the water level in the Waikato, and 11 bulldozers frantically pushed spoil into the river to stop the natural flow. The process was hampered by unexpected heavy rain which caused the river to rapidly rise, with it taking 27 hours to finally dam the river's natural course. The spillway tunnel was then constructed, which dropped at a 45-degree angle to intersect with the diversion tunnel.
In late 1949, work finally started on the dam foundations. Extensive and careful grouting of the rock took place, reaching 200 feet (61 m) below the river bed, and along the sides for a length of 1,000 feet (300 m). The grouting involved drilling thousands of holes in the rock face, and 11,000 tonnes (11,000 long tons; 12,000 short tons) of cement was used in the process.