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In principle, yes: storing water behind the Three Gorges Dam shifts mass on Earth, which can very slightly affect the planet’s rotation. The effect is far too small to notice in daily life. The often-repeated figure of a 0.06-microsecond longer day is not verified by the NASA pages cited here, which provide no calculation for that number.
How can a dam affect Earth’s rotation?
Earth’s rotation depends partly on how its mass is distributed relative to its rotation axis. A reservoir holds water in a different place and arrangement than the river and land it covers. That redistribution changes Earth’s moment of inertia; in principle, a change in moment of inertia affects the rotation rate. This is the physical basis for saying a large reservoir could alter the length of a day by a tiny amount.
This is not a change to Earth’s orbit, and it does not mean the planet suddenly spins down in a way people could feel. The effect discussed is an extremely small change in rotation, not a perceptible shift in everyday timekeeping.
What is established about the Three Gorges Dam?
The dam crosses the Yangtze River in China. NASA describes its intended purposes as flood control and hydroelectric power; it also cites navigation among the project’s benefits. NASA’s 2012 Photojournal description says the reservoir extends 660 km: NASA Photojournal: Three Gorges Dam reservoir.
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The scale of the reservoir helps explain why it is used to illustrate mass redistribution, but the dimensions alone do not establish a numerical effect on the day’s length. NASA’s 2007 account reported that about 632 square kilometers were expected to be submerged and anticipated that more than a million people would be relocated: NASA Earth Observatory, 2007.
Is the 0.06-microsecond claim confirmed?
The figure commonly repeated online is that the reservoir lengthens a day by 0.06 microseconds. The NASA pages cited here do not provide the calculation or identify a source for that exact estimate, so it should not be presented as a figure verified by those pages. The sounder conclusion is qualitative: changing the distribution of water can affect rotation in principle, but the exact magnitude needs a traceable calculation.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What the dam changes beyond rotation
The project’s scale also comes with substantial human and environmental consequences. NASA’s accounts give different relocation figures, reflecting different dates and descriptions rather than one interchangeable number:
- In 2007, NASA Earth Observatory described more than a million people as expected to be relocated.
- A 2012 NASA Photojournal caption said over 1.3 million people had been relocated.
- A 2017 NASA summary reported that construction forced some 1.2 million people to relocate: NASA Earth Science Division, 2017.
NASA also describes inundated cultural sites, silt accumulation, biodiversity concerns, and reported landslides and seismic effects, alongside hydropower, flood mitigation, and navigation benefits. These costs and benefits are part of the project’s real-world significance; they are distinct from the tiny rotational effect.
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