China's large and mysterious dam project on Brahmaputra is alarming not just India but also experts

Step aside, Three Gorges Dam. China's latest colossal infrastructure project, if completed, will be the world's largest hydropower dam, high up in the Tibetan plateau on the border with India.

China says the Motuo Hydropower Station it is building in Tibet is key to its effort to meet clean energy targets. China also sees infrastructure projects as a way to stimulate the sluggish Chinese economy and to create jobs.

But this project has raised concerns among environmentalists and China's neighbors -- in part, because China has said so little about it.

The area where the dam is being built is prone to earthquakes. The Tibetan river being dammed, the Yarlung Tsangpo, flows into neighboring India as the Brahmaputra and into Bangladesh as the Jamuna, raising concerns in those countries about water security.

What's known about the project?

China announced in late December that the government had approved construction of the Motuo project in the lower reaches of the Yarlung Tsangpo, but it has released few details about it. That includes the cost of the project, where the money will come from, what companies are involved and how many people are likely to be displaced.

The dam will be in Medog County in Tibet, in a steep canyon where the river makes a horseshoe turn known as the Great Bend, then falls about 6,500 feet over roughly 30 miles.

By harnessing the kinetic energy of that drop, the hydropower station could generate 300 billion kilowatt-hours of energy per year, the state-owned Power Construction Corp. of China, or PowerChina, estimated in 2020. That would be triple the capacity of the Three Gorges Dam, currently the world's biggest, which cost China about $34 billion to build.

China has not disclosed which company is building the dam, but some analysts say PowerChina, the country's largest builder of hydropower infrastructure, is most likely involved. The company did not respond to requests for comment.

Experts say construction in the Great Bend, a 500-meter-deep canyon with no roads, would probably take a decade because of the technical challenges.

Even the dam's basic design is unknown.

According to Fan Xiao, a senior engineer at the Sichuan Bureau of Geology who spoke to The New York Times, one proposal, which he saw as a likely approach, involved building a dam near the top of the Great Bend and diverting the water through enormous tunnels drilled into the canyon.

China's top leader, Xi Jinping, has promised that the country's carbon emissions will peak around 2030 as it replaces coal with renewable sources of energy. The ruling Communist Party, which uses massive public works projects to showcase its engineering prowess, has for years studied ways to tap into the power of the Yarlung Tsangpo.

Are there environmental risks?

The same forces that created the Great Bend pose risks to the dam China is building on it. The Tibetan plateau was formed by a collision between the Indian and Eurasian tectonic plates millions of years ago. To this day, the Indian plate is still slowly moving toward the Eurasian one, which is why the Himalayas are regularly hit by earthquakes.

Such seismic events threaten the safety of dams. Chinese officials said cracks appeared on five hydropower dams in Tibet after a magnitude 7.1 earthquake struck near the city of Shigatse this month, killing more than 120 people.

Even if the Motuo dam is built well enough to withstand an earthquake, the landslides and mudflows resulting from quakes are difficult to contain and can kill people living nearby. Experts say the massive excavation involved in dam construction could make such disasters more likely.

What about the people living there?

It is hard to know how the project is being received by Tibetans and members of other, smaller ethnic groups who live in the area. Tibet is tightly restricted by the Communist Party, which has encouraged Han Chinese people to move to the plateau and strictly controlled the practice of Tibetan Buddhism. Tibet is open to foreigners only by permit, and it is usually off-limits to foreign journalists.

In the past, Tibetans have held protests against hydropower dam projects that threatened to displace them, including a demonstration last year in Sichuan province, according to a news report.

The Motuo dam project is expected to bring more changes to Medog, which was once China's most remote county. The government has built highways into the region that have drawn tourists and adventure travelers in recent years, according to Matthew Akester, a Tibet researcher based in India.

Now, people will have to be relocated to make way for the dam, which may require farmlands and towns to be submerged. It is unclear how many people could be affected. Medog has a population of 15,000.

Tibet, which is vast but sparsely populated, does not need a lot of energy, and the dam's estimated capacity would also exceed what neighboring provinces require, Fan said. Nearby Sichuan and Yunnan have many hydropower plants, producing more energy than the region needs. And sending the power over long distances to other parts of China would be expensive.

How are India and Bangladesh reacting?

The dam could affect people living downstream in the Indian states of Arunachal Pradesh and Assam, as well as in Bangladesh. If the dam trapped sediment, that would make the soil along the river downstream less fertile and erode riverbanks and coastlines in India, said Dr. Kalyan Rudra, a professor of river science and the chair of the West Bengal Pollution Control Board, a government body.

Scientists in India and Bangladesh have asked China to share details of its plans so they can better assess the project's risks. Indian diplomats have also urged Beijing to ensure that the project will not harm downstream states. China says it has taken measures to prevent negative consequences for its neighbors.

China's secrecy is fueling mistrust, said Genevieve Donnellon-May, a researcher at the United Kingdom-based Oxford Global Society who studies water policy and environmental conflict. "Without Beijing releasing hydrological data and detailed plans for the dam, India and Bangladesh are left in the dark, so it's harder to prepare to mitigate any potential impacts from it," she said.

Both China and India have accused each other of trying to exert control over water resources for strategic or economic gain -- what some experts and officials call "hydro-hegemony." The dam could be seen as a way of projecting Chinese power near the disputed border with India, including in Arunachal Pradesh, which China claims as its territory.

Because it is upstream, "China can make decisions that directly affect the water flow downstream, raising fears in India," Donnellon-May said.

Some officials in India have proposed building a large dam in a tributary of the Brahmaputra to store water and counter any reduction in flow that the Tibet dam might cause. But Rudra of the West Bengal Pollution Control Board said such a dam could cause the same problems with soil fertility and erosion.

This article originally appeared in The New York Times.