The historic pace of land subsidence in California Central Valley, the most productive U.S. agricultural region in the U.S., drives need for extensive infrastructure fixes. A canal that delivers vital water supplies from northern California to southern California is subsiding in places. So are stretches of a riverbed undergoing historic restoration. On farms, well casings appear like mushrooms as the ground around them subsides.
4 years of drought and heavy reliance on pumping of groundwater have made the land sink faster than ever up and down the Central Valley, requiring repairs to infrastructure that experts say are costing billions of dollars. This land subsidence, at rate of more than one foot a year in some places, is not expected to stop any time soon, experts say, nor will the expensive repairs.
It is shocking how such large area is affected, said James Borchers, a hydrogeologist, who studies subsidence and says careful monitoring is necessary to detect and address sinking before it can do major damage to costly infrastructure such as bridges, foundations, and pipeline crossings, etc.
Land subsidence is largely the result of pumping water from the subsurface. As aquifers are depleted, the surface subsides. The most severe examples today are in San Joaquin Valley, where the U.S.G.S. in 1975 said half of the land is prone to subsiding. USGS researchers later called it one of the single largest alterations of the land surface attributed to humankind.
A sparse mountain snowpack in California, driest 4-year span on record, has forced farmers in the Central Valley, the most productive agricultural region, to rely on groundwater to irrigate their crops. Drought has spawned a well-drilling boom, with some tapping deep aquifers 3,000 ft down.
The Houston, Texas area had similar problems of subsidence caused by overpumping until it was decided to transition to surface-water sources from behind dams.
See: https://i2mconsultants.com/downloads/ela-iet/HouFaultGuideDecember2014.pdf
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