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Comment by KennyBlanken | Hacker News Reader

This hides one major component, however: ground compaction. When you draw down the water table, the ground compacts, and the capacity is never regained, which means you now have far less capacity in the aquifer for a particular area.

It will only get worse in overdeveloped areas or areas that overdraw their water for agriculture and industry.

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Do we have measurement of that? How worse does it get on overdraw?

there have been articles/posts with showing just how much the ground has compacted or sunk.

"overpumping caused land in the state's San Joaquin Valley to sink almost 3 feet (85 centimeters) during a recent drought from 2007 to 2010." [0]

"USGS Scientists Explain How Aquifer Compaction is Measured" [1]

[0] https://www.jpl.nasa.gov/news/overpumping-reduces-california...

[1] https://www.usgs.gov/centers/california-water-science-center...

"Further inland in California’s Central Valley, excessive pumping of groundwater for agriculture has caused the land to sink significantly. Since the 1920s, sections of the San Joaquin Valley have sunk by as much as 8.5 meters (28 feet). Groundwater pumping becomes even more problematic during droughts, exacerbating subsidence problems. Data from 2015 showed some spots subsided at rates as high as 600 millimeters (2 feet) per year."

https://www.washingtonpost.com/climate-environment/2023/05/3...

https://www.usgs.gov/media/images/location-maximum-land-subs...

Keep in mind this picture was taken 47 years ago

Also damns slowly fill with silt over their finite lifespans. When the orriville dam is past it’s useful life, there is little alternative for central CA.

interesting view - as environmentalist around here are promoting initiatives to reduce use of concrete etc to allow more water in the ground -> that would be useless then ?

> When you draw down the water table, the ground compacts, and the capacity is never regained, which means you now have far less capacity in the aquifer for a particular area.

Now that i think it over, if you're not suppose to use it (the capacity below water table) due to compaction, that capacity is useless, so it doesn't matter if it disappers ?

Porous concrete has been useless. It clogs up eventually and loss it's ability to transport water.

The groundwater disappearing is a problem if you build up ag/industry/development based on the groundwater availability and then lose that source of water with no economical alternative.

It also seems crazy in certain areas, such as where the ground freezes in winter. All those little pores will freeze and break, turning the entire concrete mass to powder.

People hate unneeded work, so in the old days, if there were large boulders of granite in fields to clear, they'd hand drill holes in the top. Then, over a few winters, the freezing water would break the granite.

It's less of a problem than you would think as water that's liquid will drain through it and snow etc doesn't expand. You generally get pot holes because water pools in an a layer and then expands and contracts, but if it's draining that's not a problem.

Also, air entrainment has long been (~1930's) used as a means of freeze thaw resistance because it allows some deformation without cracking. Porous concrete has similar flexibility.

There are technologies that have different advantages and weaknesses vs. porous concrete. For instance, TruGrid holds fine gravel in place using tiles made of recycled water bottles. It's ADA approved for wheelchairs, and certified compatible with stiletto heels (by someone that must have an absolutely bizarre certification facility).

if groundwater lowering categorically caused a lower capacity for water that was impossible to reverse in every case, the earth would not have any aquifers at all. We can see this is untrue. It's therefore not likely there's no nuance.

Historically, who was draining those aquifers? It seems that pumping large amounts of water out of the earth is a relatively new thing. On planet timescales anyway.

Historically artesian wells, possibly during earthquakes as well you'd see water leaving an aquifer. The volume on the other hand seems totally inconsistent with what we pump on a daily basis from something like the Ogallala

I absolutely do not know the process for aquifer formation, however:

* the ice age left immense amounts of water behind, including hidden under ground ice bergs that took thousands of years to thaw

* if you had a lake in a place, that sort of saturation would lead to an aquifer I think. Then the lake disappears, but the saturated ground remains, hidden from the air and sun, until drained

> including hidden under ground ice bergs that took thousands of years to thaw

Citation needed?

I think they just mean glaciers

Yeah I have no idea what they are referencing either. Ice sheets are called as such because they sit on top of the continents. Apparently North America was actually compressed downwards by the last sheet and is still basically rising back up.

Maybe they are thinking of permafrost or something? I'm not sure how deep that gets at the Northern reaches like Svalbard. But most of the land on earth is not permafrost for a long time now.

If it were as simple as water removed can never return, then all ground would eventually become impermeable over time as periodic dry seasons incrementally do their work.

Some aquifers are as he says and others aren't. Some aquifers readily refill when it rains while others cannot, or cannot on human-relevant timescales.

Water linger is what is needed. There are ways to accomplish that. But it means undoing decades of making that not happen. Then once you figure out the water linger problem you have to figure out the soil fungus/plants/animals. So it does not just all run off again. Probably the worst thing we did was decimating the beaver population. That takes time to fix.

It is not because you remove the water that you immediately compact. This takes time, so, you are probably going to lose more capacity if you do not refill within 5 years or if you refill every year.

I have no ideas about the scale, both in space and time.

The compaction associated with installing permeable concrete is in the top 10's of inches of ground at most. Typical aquifiers are 10's-100's of feet below ground surface, so that doesn't matter.

California has particularly terrible drainage. Although engineers and installers around here are correct when they point out that soil heaving is a real issue (everything is clay, and so it expands and contracts a lot), it's mostly gross incompetence from what I've seen.

The contracts we ended up signing with geological engineers, etc, all limited liability to the price of the contract. So we paid $10K to a useless engineering firm to get obviously broken designs approved by the local planning office and environmental review (the plan reviewers are also completely incompetent from what I've seen -- think "water likes to flow uphill", or "I dropped out of grade school because I don't understand trigonometry" incompetent).

The broken plans ended up costing us $150K, and now I'm good with a shovel and earth-moving equipment and material relocation logistics. It's probably illegal for us to touch the drainage without a permit, but we also are apparently legally liable if we don't maintain / repair it.

It's not just us: Tons of roads wash out, basements flood, suburban yards end up with sinkholes that could swallow a car, drains clog, roads flood, bridges wash away, etc, etc. This sort of thing happens on a widespread basis every few years.

Anyway, tl;dr: If you want to reduce the environmental impact of construction and drainage in California, mandate legal liability that includes damages + replacement / upgrade costs to a working system, and spread that liability across the engineering firms and planning commissions that are approving these plans.

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