The world’s largest dam costing £110bn will have ’12-mile tunnels’ through Himalayas

China’s Three Gorges Dam is one of the world’s largest, standing over 600 feet tall and extending for nearly 8,000 feet. The dam is so massive, it’s reputed to have slowed the Earth’s rotation. But, not content with building that monstrous edifice, Chinese engineers are now planning to build an even more gigantic dam.

The controversial Medog Dam is to be built across the Brahmaputra river, and it is slated to generate an enormous 300 billion kilowatt-hours of electricity annually, making it three times more powerful than the Three Gorges Dam.

But the project has been greenlit without any involvement from nations downstream from the site, leading to concerns that India and Bangladesh could in future be deprived of essential water supply for agriculture.

The Medog dam will be built across the Yarlung Tsangpo River, known in India and Bangladesh as Brahmaputra. Nicknamed “the Everest of rivers”, it has a unique combination of flow and gradient on the planet.

In its most vertical section, the Great Tsangpo Canyon, the river descends in an abrupt turn known as the Great Bend before crossing the border into India’s Arunachal Pradesh region.

In just one 30-mile stretch, the water falls over 6,500 feet, a dream for energy generation. Chinese authorities have predicted that the future power station could have an output well in excess of 60,000 megawatts.

Building such a huge dam in this remote, treacherous area won’t be easy, and the Medog dam is predicted to become the most expensive infrastructure project in history, with an estimated cost of one trillion yuan (about £110 billion).

The plan includes diverting half of the river’s flow, more than 2,000 cubic metres per second, through six 12-mile-long tunnels drilled into the solid rock of the Himalayan mountain range.

An intervention of this magnitude in the most seismically active mountainous landscape on the planet is unprecedented, and any structural failure could turn the dam into a real “water bomb” with devastating consequences for downstream communities.

But while the ambitious project puts China on course to achieve carbon neutrality by 2060, it has drawn significant international criticism.

A 2024 report from the Australian Strategic Policy Institute warns that “China is quietly and irreversibly working to legitimise its control over border regions, including territories disputed with India”.

“Populating these territories with civilians and infrastructure provides Beijing with a better negotiating position in border talks, allowing it to reject any agreement that involves displacing these local populations.”

The colossal dam strengthen’s China’s foothold in the region. Beijing refers to the Indian region of Arunachal Pradesh as “South Tibet” and considers it, at least partially, as part of its territory.

According to the Pentagon’s 2021 annual report on Chinese military power, in 2020 Beijing built a village with 100 houses within this disputed area with India, near the area where the Medog dam project is being developed.

This move is an emblematic example of the so-called “salami tactic”, a strategy based on making repeated small changes that, over time, alter the status quo on maps and borders. This same approach has yielded results for Beijing in its control over the South China Sea.