Sustainable Groundwater Management in California: How USGS Science Helps

Pumping groundwater can make the land sink. USGS.

In 2014, California passed the historic Sustainable Groundwater Management Act (SGMA). Local agencies must write and carry out groundwater-sustainability plans that avoid "undesirable results":

1. falling groundwater levels;
2. shrinking groundwater storage;
3. seawater intrusion;
4. declining water quality;
5. land subsidence;
6. depletion of connected surface water.

The U.S. Geological Survey supplies data, models and analysis to help managers plan for and assess each, understand trends, and test management strategies.

Groundwater levels

Water levels in wells are the basic measure of groundwater's quantity and movement. Since 1992, the USGS and the Mojave Water Agency have run a large monitoring network and drawn regional water-table maps for the Mojave River and Morongo basins (maps and data).

Water levels in the Mojave River basin. USGS.

Storage

Storage change is estimated from water levels and remote sensing, combined with models. The Central Valley Hydrologic Model has measured the Valley's large storage losses since 1962. It divides the aquifer into 20,000 one-square-mile cells and 10 layers, 50 to 750 feet thick.

Central Valley groundwater storage change (red) and surface-water deliveries (green). USGS.

Seawater intrusion

Falling water levels let seawater push into many coastal basins. Measuring it means understanding how the aquifer connects to the ocean and telling apart sources of salty water. In the Los Angeles West Coast Basin, USGS chloride studies map intrusion in three dimensions and test injection barriers (project).

Seawater intrusion monitoring in the Los Angeles West Coast Basin. USGS.

Water quality

Tracking quality means steady monitoring plus understanding how groundwater flows. Using the USGS Groundwater Ambient Monitoring and Assessment (GAMA) program and state public-health data, scientists found that natural uranium was being mobilized by human activity — especially excess irrigation water draining into the aquifer.

Uranium in groundwater of the eastern San Joaquin Valley. USGS.

Land subsidence

Heavy pumping has made land sink across California, damaging wells, buildings and highways and disrupting drainage, flood control and canals. The USGS uses satellite imagery, continuous GPS, extensometers and models to measure subsidence in the San Joaquin Valley and find solutions (subsidence).

Subsidence in the San Joaquin Valley. USGS.

Streams and groundwater

Groundwater sustains much of the flow in streams and the water in lakes and wetlands, especially in dry periods, so both must be measured and modeled together. The GSFLOW model estimated how pumping reduced streamflow on the Santa Rosa Plain, Sonoma County, from 1976 to 2010 (report).

Streamflow reduced by pumping on the Santa Rosa Plain. USGS.

Models

USGS tools include MODFLOW and integrated groundwater–surface-water models such as GSFLOW and MODFLOW-OWHM, and recharge and runoff models such as the Basin Characterization Model and PRMS.

USGS MODFLOW-based groundwater models in California. USGS.

Sources

Based on Sustainable Groundwater Management, USGS Fact Sheet 2015–3084 (version 2.0, February 2016), California Water Science Center, U.S. Geological Survey (DOI); a work of the United States government in the public domain. The illustrations come from the fact sheet's PDF.