User:Marthatnathistory/California Aqueduct

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In cases of groundwater removal, disruption to land on the surface and underground water storage can either be elastic, meaning recoverable, or inelastic, meaning permanent. Coarse-grained sediment which holds groundwater can be drained and recharged with minimal underground and surface level damage and the change that does occur is considered seasonal subsidence. However, fine-grained sediment takes longer to draw water out of and recharge and if groundwater levels are left low for too long, the compaction of the sediment is permanent and causes irreversible land subsidence.

The Central Valley, where a large portion of the California Aqueduct runs through, has been affected by the pumping of groundwater and subsequent land subsidence. Farmers in and near the Central Valley have become reliant on groundwater especially with recent droughts impacting the amount of readily accessible surface water. However, overuse of groundwater can cause irreversible damage. During the 2011-2017 California drought, a record high drought, groundwater and its storage capabilities in the San Joaquin Valley saw a sharp decline. From October 2011 to September 2015 measurements made on groundwater levels in the San Joaquin Valley’s aquifers recorded a loss of 14 km³/year, a total of 56 km³. During this same period up to 1,000 mm of land subsidence was measured in the San Joaquin Valley. Concerns around groundwater depletion have contributed to legislation to reduce the demand for groundwater and incentivize farmers to use sustainable irrigation practices.