Groundwater Info Center
Land Subsidence Monitoring

Inelastic land subsidence caused by groundwater extraction is a major problem in some regions of California and is exacerbated by additional pressure on groundwater resources during periods of drought. DWR monitors and reports on land subsidence using various methods.

Land Subsidence Reports and References

California Aqueduct Subsidence Study, July 2017
The purpose of this project is to research and study past and present subsidence reports and data, and to understand and summarize the magnitude, location, and effects on the Aqueduct. This report summarizes the significant information found, and presents the results of the data that were analyzed.

NASA Progress Report: Subsidence in California, March 2015-September 2016
New NASA InSAR satellite maps prepared for the California Department of Water Resources (DWR) in this February 2017 report, "Subsidence in California, March 2015-September 2016", show that land continues to sink at accelerating rates in certain areas of the Central Valley, putting state and federal aqueducts and flood control structures at risk of damage. Download the report and check out DWR's California Water Conditions Drought website.

NASA Land Subsidence Report: 2015
A report on subsidence in California's Central Valley, prepared for DWR by NASA's Jet Propulsion Laboratory, was released in August 2015. The report, Progress Report: Subsidence in the Central Valley, California, shows that subsidence rates of up to nearly two inches per month have occurred in some locations within the Central Valley.

Summary of Recent, Historical, and Estimated Potential for Future Land Subsidence in California
This report summarizes recent and historical subsidence and estimates the potential for future subsidence within the DWR Bulletin 118-defined groundwater basins of California. The results of this work are intended to be used as a screening tool to identify areas where the potential for subsidence due to groundwater extraction may persist and to act as a guide to focus future site-specific subsidence studies. The information contained in this report is also available on the Groundwater Information Center Interactive Map Application.

Land Subsidence from Groundwater Use in California
This report was recently released by California Water Foundation and highlights the escalating occurrence and severity of land subsidence due to groundwater pumping in California. This report provides examples of significant and far-reaching impacts of subsidence and includes recommendations to avoid those impacts. | Summary Report | Full Report |

Land Subsidence Monitoring

DWR along with the United States Geological Survey (USGS) and local agencies have monitored land subsidence in California for decades. A description of the different land subsidence monitoring methods are described below along with links to additional land subsidence information provided by the USGS.

Borehole Extensometers

Borehole extensometers are a more site specific method of measuring land subsidence. These instruments consist of a pipe or cable anchored at the bottom of a well casing. Pipe or cable extend from the bottom of the well, through geologic layers susceptible to compaction, to the ground surface. The pipe or cable is connected to a recorder that measures the relative distance between the bottom of the bore hole to the ground surface. These instruments are capable of detecting changes in land surface elevation to 1/100th of a foot. When land subsidence and water depth monitoring activities are paired together, hydraulic and mechanical properties of the aquifer system can be determined. DWR monitors 11 extensometers in the Sacramento Valley.

Interferometric Synthetic Aperture Radar (InSAR)
Interferometric Synthetic Aperture Radar (InSAR) is a satellite-based remote sensing technique used to measure changes in land surface elevation over large areas. DWR has been working with NASA Jet Propulsion Laboratory to acquire and process InSAR data to measure relative changes in land surface elevation in portions of the Central Valley and other locations throught California since 2007.
Global Positioning System (GPS) Surveying
The Department of Water Resources (DWR), together with 20 federal, state and local agencies, installed and surveyed a land elevation measurement network in the Sacramento Valley. The Sacramento Valley Height-Modernization Project allows land surface elevations to be accurately measured with Global Positioning System (GPS) technology using a consistent vertical datum known as NAVD88. The data is stored by the National Geodetic Survey. The GPS network, consisting of 339 survey monuments spaced about seven kilometers apart, covers all or part of 10 counties in the Sacramento Valley.
Additional Land Subsidence Information

Detailed descriptions of additional Land Subsidence monitoring methods are available at the following site.
USGS Land Subsidence Monitoring