The Three Gorges hydropower dam is so large that when it is full of water, the Earth's rotation will slow down and the day-long period will grow

Although the change will be small, it is undeniable its influence on the Earth's rotation.

Here's the truth: Large earthquakes can affect Earth's orbital motion, reduce the length of the day, deform the planet's surface or even cause the Arctic to move slightly. . However, all these changes are extremely small, not enough for us to feel but science still has a way to calculate the changes, no matter how small the number.

' Any action involving the movement of a large amount of matter affects the rotation of the Earth , from seasonal weather to land vehicles ,' Professor Benjamin Fong Chao said. from Goddard Space Travel Center, NASA said.

So it's not uncommon for the Three Gorges Dam, the world's largest hydroelectric project (based on an installed capacity of 22,500 megawatts), to potentially affect the Earth's axis motion. When full, the water level of the Three Gorges reservoir will be 175 above sea level ; The lake is 660 km long, 1.12 km wide and has a pit volume of up to 39.3 km ³ , meaning that the water of the Three Gorges lake will weigh up to 42 billion tons.

Three Gorges Dam.

Such a large mass will affect the rotation of the Earth, namely the moment of inertia of rotational motion . Take the example of an ice skater rotating on the spot: when their arms are close to the reel, the moment of inertia decreases and their rotation speed increases; When stretching out your hand, the rotation speed will slow down. 

The full Three Gorges lake is like stretching an ice skater with his arms out; due to a huge amount of water accumulated in one place, the mass of the Earth moves farther away from the axis of rotation and thus the Earth's rotation speed slows down. The theory is that, but the actual number is not too large, because 42 billion tons of water is nothing to the Earth's mass of 5.972 billion tons.

NASA scientists calculated that the large volume of water in the Three Gorges lake will increase the day length to 0.0000000006 seconds. If there were no other changes, and continued to assume that the lake water would remain above the same level so that the continuous day length would add up to 0.00000006 seconds, then in 47,650, the time of day would be increased by 1 second.

The influence is too small for us to feel, but at least math gives us the answer to how small the effect is.