Shagun Juthani
Subsidence is the gradual sinking of the ground. Although this can happen naturally due to tectonic activity, in recent years, it has been exacerbated by humans who have been extracting resources–such as groundwater– at unsustainable rates. This may seem counterintuitive as water is considered to be renewable resource, but extracting groundwater at a rate faster than the rate of recharge in aquifers–which are permeable layers of rock containing groundwater–is disastrous; the space between the individual sediments that was once occupied by water suddenly closes due to the lack of it, and gravity forces the land above to collapse inward as well. Blocking the space that was once filled with groundwater ultimately results in the permanent closure of vital water storage space in aquifers, diminishing their water holding capacity.
Subsidence is especially prominent in California, a state that is notorious for consuming a plethora of water for agriculture. The overpumping of water from groundwater aquifers, particularly in San Joaquin Valley, has led to an irreversible amount of subsidence. As a “region [that] produces about a quarter of the nation’s food”, it is no coincidence that 21 of its groundwater basins have been classified “as being critically” overexploited. Unfortunately, climate change has amplified this issue. Due to the onset of more frequent and devastating droughts in the face of the warming planet–which have depleted permanent sources of surface water such as snow pack–“diminished surface water supplies have led farmers [in California] to rely heavily on groundwater for irrigation in the Central Valley.” Essentially, this positive feedback loop–where increased global warming exacerbates droughts and increases our reliance on aquifer systems–results in more subsidence. Besides the depletion of future groundwater storage space, there are many other consequences of subsidence. For example, it can displace agricultural infrastructure like canals and irrigation systems. This requires reconstruction efforts that are not only expensive but also utilize countless resources. The dislocation of agricultural infrastructure in the San Joaquin Valley has “reduced the freeboard and flow capacity of the Delta-Mendota Canal—as well as the California Aqueduct and other canals that transport floodwater and deliver irrigation water—requiring expensive repairs.” During the process of reconstruction, though, “surface-water deliveries” which are generally provided by the canals, “do not meet demand”, resulting “in additional land subsidence” because of an increased reliance on groundwater.
After feeling the effects of subsidence, Californians have realized that if this issue persists at such alarming rates, there could be disastrous consequences. As a result, they have been trying to come up with ways to mitigate subsidence. For instance, the Sustainable Groundwater Management Act (SGMA) of 2014 requires “local water agencies” in California “to bring groundwater basin withdrawals and deposits into balance by 2040” by “[crafting] plans to monitor and address land subsidence” before it is too late. In addition, “California’s Department of Water Resources has given [local water] agencies” limited time to collect data regarding subsidence and “address deficiencies such as a lack of information about infrastructure potentially at risk due to land subsidence”.
Citations
“Western Droughts Caused Permanent Loss to Major California Groundwater Source” AGU BIogospherehttps://blogs.agu.org/geospace/2019/03/19/western-droughts-caused-permanent-loss-to-major-california-groundwater-source/
“Land Subsidence in the San Joaquin Valley” U.S. Geological Surveyhttps://www.usgs.gov/centers/land-subsidence-in-california/science/land-subsidence-san-joaquin-valley
“When will California’s San Joaquin Valley Stop Sinking?” Stanford Newshttps://news.stanford.edu/2022/06/02/will-californias-san-joaquin-valley-stop-sinking/
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