Power scheme intake gate work complete

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STAFF REPORTER

The $26.5million Tekapo Intake Gate Project has been completed on time and under budget, protecting one of the South Island’s key hydropower stations from Alpine Fault earthquake risks.

The 50-tonne gate is designed to stop inflows from Lake Tekapo in an emergency, such as a magnitude-7 plus earthquake that could send up to 680million tonnes of water surging around the lake.

The five-year project overcame many engineering challenges, including how to integrate modern gate technology into infrastructure and tunnels originally designed and built in the 1940s.

This included digging 22m down to the original tunnel and cutting a 20m hole in its roof to construct the new gate housing.

The gate was designed so it can be triggered manually, but will automatically close when its earthquake monitors hit a certain threshold, to act as a “dead man’s switch”.

The gate can shut completely under its own weight and does not require any electronics or hydraulic systems.

This would be vital in an emergency when power may not be available or the station’s operators are incapacitated.

Genesis chief operations officer Nigel Clark said the key to the project’s success was co-ordinated teamwork by numerous partners under lead engineering contractor Downer Engineering.

“The scale of the challenge was significant, especially when we needed to continue operating the Tekapo Power Scheme during construction,” he said.

“As a Government-classified essential services provider, construction also had to continue throughout the Covid-19 lockdown to hit deadlines.

“I am proud to say our teams have performed admirably under strict health and safety guidelines to get this done on time and under budget.”

Genesis also upgraded the Tekapo A and Tekapo B power stations during the process.

The Tekapo Power Scheme is now back to running at its full 190MW capacity, providing power to more than 100,000 homes and businesses.

Genesis will plant 400 native grasses and plants to fill the former construction site.

Key facts

INTAKE GATE PROJECT

  • The main shaft housing the new intake gate is 22m deep.
  • The tunnel the gate sits in has a diameter of 6m, and is 1.4km long.
  • The intake gate itself weighs 50tonnes.
  • Up to 130 cumecs of water flow through the tunnel equivalent to 130tonnes of water passing per second, or the weight of 65 cars per second.
  • More than 4100cum (9000tonnes) of dirt was removed during construction.
  • More than 4000tonnes of concrete was poured.
  • It took 22 months of construction, five years in the planning.
  • Up to 35 people worked on site, and a further 25 provided support, design and management.

TEKAPO POWER SCHEME

  • The Tekapo A Power Station opened in 1951. Tekapo B opened in 1977 (and is New Zealand’s only power station completed surrounded by water).
  • The canal between Tekapo A (sitting on Lake Tekapo) and Tekapo B (sitting on Lake Pukaki) is 25.5km long
  • The Tekapo Power Scheme (Tekapo A and B) produces 190MW of zero-emissions, 100% renewable electricity.
  • It powers nearly 100,000 New Zealand homes.