Images

Pre-subsidence diagram showing the relation between surface and subsurface processes with linkage to land subsidence. The linkages to subsidence deformation are briefly summarized for surface-water, landscape and groundwater flow processes.

The dominant cause of land subsidence in the Sacramento-San Joaquin Delta is decomposition of organic carbon in the peat soils. Under natural waterlogged conditions, the soil was anaerobic (oxygen-poor), and organic carbon accumulated faster than it could decompose. Drainage of peat soils for agriculture led to aerobic (oxygen-rich) conditions.

Reduced surface-water availability (associated with droughts) during 1976-77, 1986-92, 2007-09, and 2012-2016 caused groundwater-pumping increases, water-level declines to near or beyond historic lows, and renewed aquifer compaction.

Withdrawal estimates for each category represent the total amount of water removed from the water source, regardless of how much of that total is consumptively used. In most cases, some fraction of the total withdrawal will be returned to the same or a different water source after use and is available for other withdrawals.

Detailed location map of the Cuyama Valley, California watershed and groundwater basin, with the hydrologic model boundary and major rivers.

Extremely low water levels at Huntington Lake, CA in August, 2014 during the severe drought California faced from 2012 -2016.  Located in the Sierra Nevada mountain range, Huntington Lake is a reservoir operated by the U.S. Bureau of Reclamation.

Extensometers are used in land subsidence studies to measure the compaction and expansion of the aquifer system to some depth. This pipe borehole dual-stage extensometer was built in 2008 in San Lorenzo, CA and measures compaction from 10 to about 300 meters. The illustration highlights the features that can be seen in the photograph.

Standard configuration of a Sacramento-San Joaquin Delta flow and water quality monitoring station.  The U.S. Geological Survey (USGS) has operated and maintained a monitoring network in the Sacramento-San Joaquin Delta since the 1970’s.

Juvenile sand lance (Ammodytes hexapterus) (top) and surf smelt (Hypomesus pretiosus) (bottom) collected on Bainbridge Island, Washington. Scale is in inches.

The extensive withdrawal of groundwater from the unconsolidated deposits of the San Joaquin Valley has caused widespread land subsidence—locally exceeding 8.5 meters (m) between 1926 and 1970 (Poland and others, 1975; fig. 2), and reaching 9 m by 1981 (Ireland, 1986).

Generalized surface geology of the Anza–Terwilliger study area, Riverside and San Diego Counties, California (modified from
Rogers, 1965).

One of the wells that's part of the groundwater monitoring network in Anza Valley, CA.

Malakoff Diggins State Historic Park

In 2012, the Groundwater Ambient Monitoring & Assessment Priority Basin Project (GAMA-PBP) began water-quality assessments of shallow aquifers, the groundwater resources typically used for private domestic and small system drinking-water supplies.

The All-American Canal (AAC) in southern Imperial County, California, has historically been unlined, resulting in substantial losses to seepage. In 2006, the Imperial Irrigation District, under a contract with the United States Bureau of Reclamation, initiated a project to build a concrete-lined canal parallel to 23 miles of the earthen AAC.

Location map showing the location of facilities along the Colorado River and Yuma agricultural area adjacent to the United States-Mexico Border (USBR, 2011).

A USGS Hydrologist purges a groundwater monitoring well in preparation for water-quality sampling in the Imperial Sand Dunes Recreation area, Imperial Valley, California.  This sampling was done as part of the Forecasting Total Dissolved Solids Concentrations of Groundwater from the Lower Colorado Water Supply Project study.

The Imperial Sand Dunes Recreational Area, located in Imperial County in the far southeast corner of California. It is home to a groundwater well field that is part of the U.S. Bureau of Reclamation's Lower Colorado Water Supply Project.

The Central Valley Hydrologic Model (CVHM) is built on knowledge from USGS and other Federal, State, and local studies. The CVHM was constrained by comparing simulated and historically observed groundwater levels, streamflows, and subsidence.

A USGS Hydrologist re-develops a monitoring well to ensure a good hydraulic connection is present between the perforations in the well and surrounding aquifer.  This work was being done as part of a groundwater system characterization and groundwater quality study being conducted along the All-American Canal that runs through the area.

A scientist from the USGS California Water Science Center taking well water sample in California.