Sad and scary

[Craig Good]

Time lapse of Folsom Lake drying up.

[jack saunders]

Did you guys see that KQED/Center for Investigative Reporting story over the weekend about SUBSIDENCE?  Hot new topic in the central valley where the dirt you walk on is subsiding INCHES PER MONTH.  "The ground I am standing on was ten years ago over my head," said the reporter.

The breaking point in this tale reached page one very soon -- perhaps this winter if we get a major el nino event.  The levees look like ancient sidewalks, all cracked up.  The camera showed the unaided eye  four in either direction, and the report claimed they're all over the system.  Dump Texas or So. Carolina rains on them and levees go catastrophically....because the ground water is being pumped out.

Government has stepped in boldly -- new law will, for the first time, regulate ground water pumping.....to take effect in 25 years (from now).  Agri biz has a lot of clout in Sacto.

 

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From: Craig Good <clg...@gmail.com>
To: Ipse Dixit <Ipse-...@googlegroups.com>
Sent: Tuesday, October 13, 2015 12:12 PM
Subject: [Ipse Dixit] Sad and scary

Time lapse of Folsom Lake drying up.

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[Brian Howell]

Aquifers are measured by three criteria: capacity, permeability, and porosity. The first is a measurement of an aquifer's total capacity to hold water. The second is how easily water flows through the aquifer; it's dependent both upon the mineralogy (some rocks hold onto water molecules more strongly than others) and the third criterion: porosity. Porosity is how much space to hold water there is per unit volume of aquifer. Obviously, an aquifer with larger pores (small holes within it in which water can accumulate) will hold more water per unit volume than one with smaller holes; larger pores also often—but not always—mean greater permeability, too. A highly porous stratum can be thought of as being sponge-like in construction, if not actual material. Aquifers are created when a porous stratum of rock or sand becomes overlain with one or more impermeable strata. 

Most people who've studied physics know that liquids are nearly incompressible. During the creation of an aquifer stratum, water is trapped in its porous material. When topped by other strata, the hydrostatic pressure of the water trapped in the aquifer can, in part, support the load of overburden. This is especially true for highly porous aquifers. 

Regardless of whether an aquifer is recharged (by rainfall or groundwater through a region where a portion of the aquifer is exposed to surface water; what hydrologists call a zone of recharge), pumping too much water from an aquifer (e.g., faster than it can be recharged) will significantly reduce the hydrostatic pressure within the aquifer. For a highly porous, spongy aquifer, this loss of structural support within the aquifer stratum coupled with the weight of the overburden can cause the pores to collapse into themselves. On the surface this is experienced as subsidence. 

Okay, thanks for the science lesson, Brian. What's the point?

When an aquifer collapses, it permanently loses capacity. No amount of water flowing into the aquifer—if any—is going to be able to generate sufficient pressure to lift the overburden and restore the porosity of the aquifer. In other words, once collapsed, then permanently collapsed; those farmers who are pumping dry Central Valley aquifers—many of which do recharge, albeit slowly—are destroying those aquifers. Even if the rains come, those former aquifers will never again be available in times of future drought.

[jack saunders]

Brian -- when you speak of an aquifer collapsing, I'm assuming you're speaking literally.....and some are quite large.  Would their collapse be felt like an earthquake to nearby cities?

 

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From: Brian Howell <bdho...@gmail.com>
To: Ipse Dixit <Ipse-...@googlegroups.com>
Cc: clg...@gmail.com; jack...@pacbell.net
Sent: Wednesday, October 28, 2015 7:28 AM
Subject: Re: [Ipse Dixit] Sad and scary -- that and SUBSIDENCE

Aquifers are measured by three criteria: capacity, permeability, and porosity. The first is a measurement of an aquifer's total capacity to hold water. The second is how easily water flows through the aquifer; it's dependent both upon the mineralogy (some rocks hold onto water molecules more strongly than others): Porosity is how much space to hold water there is per unit volume of aquifer. Obviously, an aquifer with larger pores (small holes within it in which water can accumulate) will hold more water per unit volume than one with smaller holes; larger pores also often—but not always—mean greater permeability, too. A highly porous stratum can be thought of as being sponge-like in construction, if not actual material. Aquifers are created when a porous stratum of rock or sand becomes overlain with one or more impermeable strata. 

[Brian Howell]

Interesting question, Jack. As far as I know, aquifer compaction (the proper term) can cause tremors—albeit they tend to be rather small, because the subsidence is gradual. That being said, they can also cause fractures and even, apparently, increase orogeny: apparently the Sierra Nevada are rising at a faster rate than in the past because we've permanently pumped the equivalent of Lake Tahoe from Central Valley aquifers; millions and millions of tons of water.

https://www.wwu.edu/content/wwu-geologist-sheds-light-impacts-human-caused-groundwater-depletion-seismicity-and-mountain

A good, brief read.

http://news.nationalgeographic.com/news/2014/08/140819-groundwater-california-drought-aquifers-hidden-crisis/