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How Infamous Hydroelectric Dam Changed Earth’s Rotation

“Powerful” does not actually do this astonishing (and VERY controversial) structure justice. Since the $30 billion project was announced, Chinese officials have faced heavy inquiry from both researchers and environmental activists like.

Many believe that the dam will eventually result in disaster. Some worries include the dam trapping pollution, generating earthquakes and landslides, uprooting citizens (more than 1.3 million people have by now been forced to relocate), and abolishing historical locations – along with the habitats of endangered animals. (The government lastly conceded that the project was ill conceived – after years of naming the dam one of the most remarkable pieces of engineering in Chinese history – but the damage is already done.)

The last 32 generators (each proficient of producing 50 MW of power) went into action at the end of July last year. The gushing water produced by the dam has sufficient power to produce about 22.5 million kilowatts (22,500 megawatts) of energy (the estimates vary), which is equal to about FIFTEEN nuclear reactors and, of course, it does not cause worries about radioactive materials being released (which is a very good thing, specifically after events like the Chernobyl and Fukushima nuclear disasters) – so the disastrous effects can be annulled by most, mainly due to the fact that it’s a clean, effective way of rendering energy for a booming population.

Wondering how this could possibly have an influence on the Earth’s rotation? Here’s a wonderful source that breaks it down further:

“Three Gorges Dam crosses the Yangtze River in Hubei province, China. It is the world’s biggest hydroelectric power station by total capacity, which will be 22,500 MW when finished. When the water level is at maximum….it will flood a total area of 632 km2 of land. The reservoir will have about 39.3 cubic km (9.43 cubic miles) of water. That water will weigh more than 39 trillion kilograms (42 billion tons).

A shift in a mass of that size will influence the rotation of the Earth due to a phenomena known as “the moment of inertia”, which is the inertia of a rigid rotating body with respect to its rotation. The moment of inertia of an object about a given axis defines how hard it is to change its angular motion about that axis. The longer the distance of a mass to its axis of rotation, the slower it will spin. You may not know it, but you see examples of this in everyday life. For example, a figure skater trying to spin faster will draw her arms tight to her body, and thereby decrease her moment of inertia. Likewise, a diver trying to somersault faster will bring his body into a tucked position.

Raising 39 trillion kilograms of water 175 meters above sea level will rise the Earth’s moment of inertia, and thus slow its rotation. Though, the impact will be exceptionally small. NASA researchers calculated the shift of such a mass will increase the length of day by only 0.06 microseconds, and make the Earth only very faintly more round in the middle and more flat on the top. It will also shift the pole position by about two centimeters (0.8 inch). Note that a shift in any object’s mass on the Earth relative to its axis of rotation will change its moment of inertia, although most shifts are too small to be measured (but they can be calculated).”

Not to worry, however. Earth’s rotation changes normally, with many different variables added into the equation. First, we have the moon slowly receding from the Earth changing Earth’s rotation ever-so-slightly.  Earthquakes (like the mega quake in Japan back in 2011) also help along the process (the same quake changed Earth’s rotation by 2.68 microseconds). Additionally, every 5 years (or so), the length of the day increases and decreases by about a millisecond, or about 550 times bigger than the change caused by the Japanese earthquake.

Still, this knowledge begs many interesting questions. Namely, how far is too far? Individually, these things don’t make much of a difference one-way-or-another, but together, who knows.

what are your thoughts?

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