Once land subsides, it can never rise back up to where it had been. Worse, constant pumping of water from aquifers alters their structure, making them less able to hold water. The San Joaquin Valley in California is ground zero for unregulated groundwater pumping. Yes, California finally passed a law regulating groundwater pumping. However, it will be years before it is implemented and it’s mostly toothless. Meanwhile, crucial aquifers are overpumped, the earth is subsidizing, and aquifers canna take any more of this, captain.
Mavens Notebook has a comprehensive article on subsidence in the Central Valley. It is required reading for water wonks! Subsidence is some areas is now a foot a year and isimpacting the ability of crucial canals to carry water southward.
It’s been called the largest alteration of the earth’s surface. In the San Joaquin Valley, since the 1920s, farmers have relied on groundwater to varying degrees, and over time, overpumping of groundwater basin has caused the land to subside – over 30 feet in some locations.
We care about land subsidence for two reasons: Infrastructure damage and flood protection and damages to our natural resources, she said. “Water conveyance systems and other water infrastructure get damaged by subsidence because it’s happening at different rates at different locations. If the whole San Joaquin Valley was subsiding at the same rate and in the same way, then nobody would really care, but it’s this differential subsidence, the different amounts of subsidence in different places that really damages canals, roads, railways, pipelines, bridges – anything that crosses these areas of differential subsidence can get damaged.”
Canals are particularly sensitive because gravity is oftentimes used to move water, and this means that every point downstream needs to be at a lower elevation than every point upstream or pumps are needed.