Sinking Land Meets its Match: Science and Technology
The San Joaquin Valley has sunk almost two stories in the past hundred years.
The phenomenon is known as land subsidence, and can occur when groundwater is pumped out faster than it can “recharge.” In California, water is as valuable as gold in come circles, and during the recent drought Californians depended more heavily on groundwater.
Unfortunately, this dependency is a triple-edged sword for San Joaquin Valley residents. Compounding the issue of over-drafting the valley’s groundwater budget, clay layers underground compact when water is pumped out. Then, when water becomes more plentiful and the underground storage begins to fill again, the clay layers can’t absorb as much water as they once held because the clay particles have gotten stuck together.
On the other hand, if you drain a layer of sand or gravel, the little rocks keep their orientation and the spaces between them, which are then able to refill with water when the time comes.
And to tie it all together, land subsidence puts the area at higher risk for flooding when the rains return due to damaged levees.
To summarize, over-pumping groundwater:
1. Drains the water from the aquifer
2. Decreases the ability of the aquifer to store water underground in the future
3. Causes land to sink and infrastructure to fail, making it more likely to flood homes and damage residential water supply during times where high-volumes of water are moving through the system.
While the land subsidence in the San Joaquin Valley has been an issue for a long time, there hasn’t been many innovative solutions to the issue. The go-to has been to pump less groundwater. But when it’s a question of the height of the land or whether your farm produces enough profit to feed your family, it’s obvious which priority has been winning out in the past few drought-stricken years.
But the solution seems obvious now: avoid pumping water from the clay layers. This is a little trickier than it sounds, of course. Firstly, this is all underground, so we need to figure out how to tell where the clay layers are and how to avoid them.
This is when our friends, Science and Technology, come in. Geophysical electromagnetic methods (using electricity and magnetism to understand the geology of the land) we can “see” into the ground beneath our feet to identify different layers of rock or sand or clay. This way we can essentially build a 3D map and use it to drill wells and pump groundwater more responsibly.
In a perfect world, the answer to our surface water drought would be to just pump groundwater. And the answer to our groundwater drought would be to just bide our time until it rains.
But with climate change, our surface water will be more scarce until winters like 2016–2017 in California where surface water rained out onto our land and into the ocean quicker than the groundwater could recharge. And this is only likely to get worse since our climate is continuing to warm and our population and demand for water is also growing.
So, Science and Technology, can I buy you a drink?
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