New data released on January 29 measure changes in land subsidence in the Sacramento Valley in Sacramento, California, over the past nine years, finding the greatest land surface declines near the city of Arbuckle in Colusa County.
According to the Sacramento Valley GPS Subsidence Network Report and accompanying fact sheet, most of the valley has experienced little to no subsidence, however, land in the Arbuckle area has sunk 2.14 feet compared with baseline measurements recorded in the same location in 2008. The report was led by the California Department of Water Resources (DWR), in coordination with 19 state and local agencies.
“We’ve long known that excessive groundwater pumping causes subsidence, which is one of the many reasons we’ve pushed for sustainable groundwater management and pursued innovative tools to better manage and report subsidence throughout the state,” said DWR Director Karla Nemeth. “Data provided by studies like this inform water managers and owners of large infrastructure so they can plan for and prevent against subsidence.”
Land subsidence can damage critical infrastructure, including water delivery systems, levees, roads, and bridges. In 2017, the DWR worked with NASA to release a report on San Joaquin Valley subsidence citing areas along the California Aqueduct that have experienced almost two feet of subsidence over three years.
The Sacramento Valley survey results were collected as groundwater levels were recovering from the severe drought of 2012-16, which saw groundwater levels in much of the state reach historic lows. Compared with 2011 pre-drought groundwater levels, the largest decreases were observed in Glenn and Colusa counties at 58 to 43 feet, respectively. Field work indicates that groundwater levels have recovered an average of seven feet, but more frequent and more comprehensive monitoring is needed to more accurately detail the impacts of droughts and high-water years on groundwater levels and subsidence.