Sinking Lands, Damaged Infrastructure: Will Better Groundwater Management End Subsidence?

In the midst of the COVID-19 crisis, work continues on managing groundwater for long-term sustainability, as required by California’s landmark Sustainable Groundwater Management Act (SGMA). In January, water users in 21 critically overdrafted basins delivered their groundwater sustainability plans to the state Department of Water Resources. In this series , we examine the 36 plans submitted for 11 critically overdrafted basins in the San Joaquin Valley—California’s largest farming region, where excess pumping is a major challenge.

What is subsidence, and why does it matter?

Excess groundwater pumping can compact soils, causing land to sink. Because this subsidence can damage costly infrastructure, avoiding it is an important reason to manage groundwater.

Subsidence due to groundwater pumping has been occurring in the San Joaquin Valley for almost a century, but it accelerated during the 2012–16 drought. Subsidence has damaged some critical water conveyance arteries, including the Friant-Kern Canal (40% of capacity lost in some stretches), and the California Aqueduct (more than 20% of capacity lost). Bridges over these and other canals are sinking, a local dam can’t hold water anymore, and stretches of the high-speed rail track have been designed to prevent damage from future subsidence.

Subsidence can also permanently reduce the capacity of aquifers to store water. Valley aquifers may have lost as much as 3.25% of their capacity from soil compaction during the 2012‒16 drought.

This infrastructure damage doesn’t just affect the individual farms or water agencies that are pumping groundwater—it affects other parties, both locally and many miles away. Mitigating damage will cost many millions, if not billions, of dollars.

How does SGMA require plans to address subsidence?

Under SGMA, land subsidence is one of the six undesirable results that every groundwater sustainability plan should […]