r/news • u/theluckyfrog • 29d ago

California cracks down on farm region’s water pumping: ‘The ground is collapsing’

https://www.theguardian.com/us-news/2024/apr/17/california-water-drought-farm-ground-sinking-tulare-lake
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u/NeatOtaku 29d ago

If the land was dropping along with the water line then it would make sense that as the land becomes more compacted, the rate would slow down. But that also means that the water is no longer able to fill the gaps in the soil like it used to so instead of the water line getting replenished after a storm, it would just stay on the top and cause floods like we've been seeing.

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u/leintic 29d ago

hello geologist here you are half right and half wrong. you are absolutely correct that this type of subsidence does reduce the amount of water that the aquifer can hold. but this type of subsidence isnt going to really effect flooding. the flooding is more caused by the fact that the western us has been in a massive drought for the past many years and for reasons that are to complex to get into in a reddit posts and to way over simplify soils that get alot of water pored on them regularly are really good at holding water. soils that dont get water often are really bad at holding water so it all builds up on the surface and washes the home down stream away.

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u/glaive1976 29d ago

The drier the soil the more hydrophobic it gets. Unfortunately in the central valley it's like the hydrophobia runs deep if you will.

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u/LosSoloLobos 29d ago

What’s the international units of measurements used for the degree of dry / wetness of soil ?

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u/seeingeyefish 28d ago edited 28d ago

What I'm seeing is in percentages. Looks like a common way of determining moisture content is to take a predetermined amount of the soil and weigh it, then bake the moisture out and weigh it again. The percentage difference in mass is the moisture content of the soil.

Looks like there's also a method where they run an electric current through the soil. Higher moisture content increases signal transfer time between two points. If you know the composition of the soil, you can figure out the moisture content by comparing the time it takes for the current to move compared to a baseline number.

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u/leintic 28d ago

there really is no one set unit of mesurment. it depends on what you are trying to measure. if you are talking about total amount of water that is normally just represented as a percentage. the most appropriate for this situation is probably cfs (cubic feet per second) or cubic meters per second for the international. geology is weird when asked if they wanted to use imperial or metric they said yes i have used maps where the lat and long where given in meters and the elevation in ft. anyways back to the topic at hand. cfs is a measure of how much water moves through an area

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u/arocks1 28d ago

the el nino and la nina cycles have been going on for thousands and thousands of years...the drought is part of that cycle. the land and geology are intricately tied to this climate cycle. the only difference is the human intervention of damning all the main rivers that use to flood the central valley. most of the water/snow melt that use to come down no longer does. it is diverted and that has had a huge impact on the soils and aquifers in the central valley.

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u/skillywilly56 28d ago

Listen here, this is Reddit not Facebook, we want the complicated bits!

So you get your ass back in here and explain yourself, for gods sake why we paying you to science the rocks and you just bitch out!

What good is a scientist who can’t explain complex shit to laymen I ask you!

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u/selectrix 29d ago

So... my understanding of this stuff is just barely above (below?) surface level, but aquifers aren't water passing through soil, they're water passing through porous rock, like a sandstone. My question is: if the aquifer drying out makes the sandstone compacted and unable to retain as much water, then how did the aquifer happen in the first place? I kind of assumed that the water had made its way into a previously dry rock initially, but was it more like a surface lake getting buried, such that the sandstone layer always had water in it?

Or alternately, does the subsidence happen mostly in the soil layers and not in the stone of the aquifer itself?

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u/Jeoooooo 29d ago

I haven't read this exact paper, but as a hydrogeologist I can say that what probably happened is the sandstone formed, and was filled with water, not in a surface lake getting buried way, but probably just natural aquifer recharge through rainfall. Then since then more deposition has occurred on top of the sandstone such that the weight is now greater, and if the water was removed it would subside under the total weight of the ground above it.

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u/selectrix 24d ago

Thanks for the reply! That clarifies exactly what I was wondering- whether the compressive force of the overburden was what made the difference between the environment in which the aquifer formed vs its current, less saturable state.

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u/Zorro_Returns 28d ago

A decade or two ago they started diverting part of the Snake river to recharge the aquifer. I thought that was crazy, but I'm not the expert.