Surprising effects of pumping groundwater 1

[GregLocock]

You'll have seen the alarmist stories about cities sinking and being drowned. All good fun designed to make little girls scared.

One of the main reasons is that we pump groundwater out of artisanal basins. This study claims we pumped 2150 billion tonnes between 1993 and 2010, which is equivalent to a sea level rise of 6mm. So that's about 2 years of normal sea level rise due to us, in 17 years. Remember the kerfuffle about 'accelerating' sea level rise?

The other surprising thing is that this has been modelled to show that it has shifted the axis of rotation of the Earth. It isn't important, but it is interesting.

https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2023GL103509

Cheers

Greg Locock


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[TugboatEng]

A similar claim was made about 3 Gorges slowing down the rotation or Earth.

 

[BridgeSmith]

A similar claim was made about 3 Gorges slowing down the rotation or Earth.

I'd like to see that story; it would be good for a laugh. I don't think anything tops World Jump Day, though. I about fell off my chair laughing when I read about that.

 

[TugboatEng]

Here is one example but it's behind a paywall. I'll keep looking for others. I'm trying to find pre-Obama articles so they aren't loaded with obligatory climate change nonsense.

https://www.nytimes.com/1996/03/03/...y-are-altering-earth-s-orbit-expert-says.html

 

[dik]

You guys disappoint me, but I'm not surprised. As engineers, you should realise that a large, quick spinning semi-solid object (the tangential velocity is fairly high...1470 fps). 88fps = 60mph. is going to experience some stress if the geometric properties are altered. This happens with change in sea level or removing ground water (if the groundwater is immediately replaced there should be little effect). The effects of the 3 Gorges dam pale in comparison (even that can have an effect).

I have no idea of the effect these events will have on said spinning mass, but there could be a change in forces in the tectonic plates, etc. It's easy to mock this because it seems so far fetched. I do not know if this is happening, but the possibility is there. Were dealing with huge forces on a 'semi-plastic' object. I don't know what the earth and it's crust would be catagorised as.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[BridgeSmith]

You guys disappoint me, but I'm not surprised. As engineers, you should realise that a large, quick spinning semi-solid object (the tangential velocity is fairly high...1470 fps). 88fps = 60mph. is going to experience some stress if the geometric properties are altered.

The feeling is mutual. I'm disappointed that, as an engineer, you don't seem to recognize that 1) the shift in center of mass of the Earth by the building of a dam and the creation of a reservoir, or pumping a few million gallons of water to the surface from a few hundred feet down, is wholly negligible, and that 2) the change in the inertia of the Earth by a few mm rise (or a several foot rise) of the sea level is equally negligible.

 

[dik]

Just because it may be 'far fetched', can you provide me with any information to refute this? Simple mechanics would indicate that there are huge forces involved. We are looking at huge forces and huge amounts of energy.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[btrueblood]

"Just because it may be 'far fetched', can you provide me with any information to refute this? Simple mechanics would indicate that there are huge forces involved. We are looking at huge forces and huge amounts of energy."

Distributed over an even more huge (or yuge) ball of rock.

 

[BridgeSmith]

Distributed over an even more huge (or yuge) ball of rock.

Exactly. A change of even a few feet in the diameter across Earth's equator is negligible for a spheroid of 7926 miles (41,850,000 feet) equatorial diameter.

 

[dik]

...with a tangential velocity of 1470 fps... based on what. How do you know it's negligible? We are dealing with huge forces/energy. Or are you just wishing that was the case? Apparently the reduction in ground water has had an influence on the tilt of the earth poles... I'd have never 'guessed' that.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[BridgeSmith]

Apparently the reduction in ground water has had an influence on the tilt of the earth poles.

You have a credible source for that?

How do you know it's negligible?

I did the math. Calculating the moment of inertia of a sphere is not that hard. Neglecting the decrease in moment of inertia at the poles and the lesser density of water compared to the other materials making up the Earth, the change in moment of inertia is the change in the diameter to the 4th power. Even with those 2 conservative assumptions, the change in the moment of inertia for a 3' increase in the diameter of the Earth is .000000287. That would theoretically slow the rotation of the Earth, making each day a couple hundredths of a second longer. FYI, slowing the Earth's rotation would theoretically make the earth less oblate, decreasing the stresses on the tectonic plates, not increasing them.

 

[SwinnyGG]

How do you know it's negligible? We are dealing with huge forces/energy

Are you serious?

Moderately big numbers are still tiny percentages of gargantuan numbers.

The earth weighs 6 x 10²⁴ kilograms

'2150 billion tonnes' of water is 0.0000000000036%. That's 3.600134e-11 percent.

If the earth were the size and mass of a basketball, the equivalent would be to take 0.0000000216 grams of mass out of the ball from a depth of .001 mm or so, and redistribute that mass in a way that results in a diameter increase of 0.000000118 mm.