China's construction of what is expected to become the world's largest hydropower project on the lower reaches of the Yarlung Zangbo river in Tibet has reached a critical juncture with fresh geological safety concerns. According to a report in the South China Morning Post, Chinese geologists have identified an active fault line directly beneath the mega-dam project, warning that it could pose risks to the infrastructure's long-term stability. The latest findings from Chengdu University of Technology reveal that the Paizhen Fault, a major fault in the Earth's crust capable of generating powerful earthquakes, has remained highly active since the Pleistocene Epoch. The researchers conclude that regional seismic activity could trigger landslides and slope failures, threatening both the structural integrity of the project and the safety of construction personnel. To reduce these risks, the researchers recommend reinforcing the surrounding slopes and implementing additional landslide mitigation measures. The study establishes four important scientific points: an active geological fault intersects the proposed reservoir area, the fault has remained active into relatively recent geological history, reservoir loading could plausibly interact with this fault through recognised mechanisms of Reservoir-Induced Seismicity, and these findings originate from Chinese scientific institutions themselves, lending them considerable credibility.
The Medog Dam or Yarlung Tsangpo Hydropower Project is being constructed at the river's great bend in Medog County in Tibet, where the Yarlung Tsangpo makes a sharp U-turn before entering Arunachal Pradesh as the Siang river and eventually becoming the Brahmaputra. Designed around five cascade power stations, the project is expected to have a combined installed capacity of more than 60 gigawatts. Construction began in July of last year and is currently projected for completion in 2033. The project is expected to generate over 300 billion kilowatt-hours of electricity annually, almost three times the output of the Three Gorges Dam, sufficient to meet the yearly power requirements of over 300 million people. With a total investment of 1.2 trillion yuan (approximately ₹1.5 trillion), it is expected to become the world's biggest infrastructure project once completed, surpassing China's renowned Three Gorges Dam. The dam is being built on the lower reaches of the Yarlung Tsangpo in Tibet's Medog County, one of the world's deepest river gorges, where the river drops around 2,000 metres over a stretch of nearly 50 kilometres, creating one of the world's richest hydropower resources.
The multi-billion-dollar project is situated close to the Indian border in Arunachal Pradesh, raising both geological and water security concerns. An Indian government analysis seen by Reuters estimated that the project could reduce dry-season flows by as much as 85 per cent under some conditions. It also estimated that the project might enable China to divert up to 40 billion cubic metres of water, slightly more than one-third of the annual flow received at a key border point. Arunachal Pradesh Chief Minister Pema Khandu has described the project as a 'ticking water bomb', warning that reduced flows during reservoir filling or sudden releases could threaten communities along the Siang. The controversy has fueled broader criticism that China is using its control over Tibet's headwaters as a strategic geopolitical tool, with officials and experts worrying that the dam could reduce water flow along one of the region's most important river systems. The principal concern is therefore not total water quantity but control over timing, as China contributes only about one-third of the Brahmaputra's annual flow, with most water originating from monsoon rainfall and tributaries within India and Bhutan. However, experts note that hydrologists say China cannot permanently stop the Brahmaputra from flowing into India because the river receives substantial additional water from heavy monsoon rainfall and numerous tributaries after entering Arunachal Pradesh and Assam.
India has accelerated plans for its own hydropower development in Arunachal Pradesh in response to China's dam-building efforts. According to Reuters, India is pushing forward with the Siang Upper Multipurpose Project (SUMP), an 11,000 MW hydroelectric and flood-control mega-dam proposed on the Siang river in Arunachal Pradesh's Upper Siang and Siang districts. Led by state-run NHPC, the project would become India's largest hydropower station if completed, generating around 47 billion units of electricity annually and projected to cost nearly ₹1.5 trillion. Beyond electricity generation, this project is envisioned as a strategic storage reservoir capable of buffering sudden upstream releases while maintaining dry-season flows, providing India with greater operational flexibility. However, it presents an important paradox as SUMP would be located within the same tectonically active Himalayan belt, confronting many of the same geological challenges now identified on the Chinese side. India has also approved investments of more than $4 billion for two major hydroelectric projects along the Brahmaputra, including the 1,720 MW Kamala project estimated at ₹260.7 billion and the 1,200 MW Kalai-II project costing ₹141 billion. India plans to develop more than 76 GW of hydropower capacity in the Brahmaputra basin by 2047 through a transmission investment programme worth $77 billion.
Beyond earthquakes and floods lies a slower but equally important issue—sediment transport. The Brahmaputra is among the world's most sediment-rich rivers, with these sediments replenishing fertile floodplains, maintaining the famous river islands of Assam, reducing erosion, and ultimately sustaining the vast delta of Bangladesh. Large reservoirs inevitably trap much of this sediment, with reduced sediment supply over decades potentially altering river morphology, accelerating bank erosion, diminishing agricultural productivity, and weakening the natural capacity of the river system to counter land subsidence. The worst-case scenario is not a disaster confined to one side of the border, but a simultaneous regional emergency affecting infrastructure, communication, transportation, and disaster response across both countries. By the time the Brahmaputra enters Bangladesh as the Jamuna, it carries the cumulative effects of everything occurring upstream, with any alteration in river flow, reservoir operation, sediment transport, or flood timing ultimately converging upon the densely populated Ganges–Brahmaputra–Meghna Delta, home to tens of millions of people. Ironically, Bangladesh—the country facing perhaps the greatest long-term consequences—has no formal trilateral framework with either India or China governing Brahmaputra management, making regional cooperation essential for addressing these complex transboundary challenges.
India and China do not have a comprehensive treaty allocating the Brahmaputra's waters, though they do have agreements covering hydrological information and an expert-level mechanism for discussing transboundary rivers. The project's location at the river's great bend in Tibet means it controls the timing and volume of water releases to a certain extent, raising downstream water security concerns for India and Bangladesh. The original MoU on sharing hydrological data for the Brahmaputra was signed in 2002 and renewed in 2008 and 2013. India and China also have a separate agreement covering the Sutlej River, originally signed in 2005 and renewed in 2010. In a written reply in the Rajya Sabha on February 8, 2018, the Ministry of External Affairs confirmed that China did not provide hydrological information on either the Brahmaputra or the Sutlej during the 2017 flood season despite existing bilateral Memorandums of Understanding. China resumed sharing hydrological data on the Siang River on May 15, 2018, under the bilateral MoU that requires Beijing to provide river flow information during the flood season from May 15 to October 15. The findings contrast with Beijing's longstanding assertions that the project has been designed to the highest safety standards and would help reduce disaster risks in the region. The announcement of China's construction has generated intense discussion across South Asia, with the Tibetan Plateau being the source of several of the world's longest rivers, making it a critical water resource for hundreds of millions of people across Asia.
