California’s groundwater

Groundwater in California has received a lot of attention lately, and for good reason:  We use a lot of it.  So much so, California has been identified as the heaviest groundwater user in the United States, with approximately 16% of the nation’s groundwater supplies being extracted from the state’s aquifers.

Irrigation Central Valley #3 08-2008 smallerGroundwater is often described as a ‘hidden resource’; but because it cannot be directly seen, it is likely most Californians do not give much thought to the economic benefits that vast groundwater supply has added to the State,  nor consider it’s value. But it is unlikely that California could have achieved its present status as the largest food and agricultural economy in the nation and eighth largest overall economy in the world without groundwater resources.

These economic benefits have not come without many costs: the diminished quantity and degraded quality of groundwater resources, the infrastructure damaged by land subsidence, the decline in ecosystem services provided by the interaction of groundwater and surface water, and the increased energy required to bring the groundwater to the surface.

Many of the state’s groundwater basins are being managed sustainably – meaning that withdrawals do not exceed the amount replenished by man or by nature; but some basins, especially those in major agricultural regions in the southern Central Valley and Central Coast, groundwater withdrawal exceeds the amount that is recharged, causing conditions of overdraft and threatening this vital resource.

California's groundwater use by the numbers
California's groundwater basins

Groundwater use and overuse

Kern Water Bank Groundwater Pump #2Groundwater can be recharged in many ways: by precipitation, by water that leaks into aquifers from surface waters, by intentional recharge efforts, by irrigation water applied in excess of what crops use, or even inadvertently from leaky pipelines and canals.

There is a balance that occurs when the amount pumped out approximates the amount of recharge; however, if more water is pumped out than is recharged, the groundwater basin can become overdrafted.

Groundwater overdraft can have numerous impacts:

Increased pumping costs, new wells to be drilled ...
Water quality degradation ...
Seawater intrusion ...
Land subsidence ...
Depletion of surface water ...

The Sustainable Groundwater Management Act (SGMA)

gov signs gw legisCalifornia depends on groundwater for a major portion of its annual water supply, and sustainable groundwater management is essential to a reliable and resilient water system. In recognition of this, Governor Brown signed a three-bill legislative package of laws collectively known as the Sustainable Groundwater Management Act (SGMA) in September of 2014 that set in motion a plan to sustainably manage the state’s groundwater basins.

SGMA basics

The legislation defines roles for local agencies, the Department of Water Resources, and the State Water Resources Control Board.

The role of local agencies
The role of the Department of Water Resources
The role of the State Water Resources Control Board

DWR’s Water Available for Replenishment Report

The Sustainable Groundwater Management Act (SGMA) directed the Department of Water Resources to do a number of things, one of them being to prepare a report on the water available for groundwater replenishment in the state.  In January of 2017, the draft Water Available for Replenishment report was released.

More information

Statewide groundwater level monitoring

Information on the state’s groundwater levels is available through the California Statewide Groundwater Elevation Program, or CASGEM.

CASGEM-logoCASGEM is the state’s long-term program to collect and track groundwater elevations statewide. The program is a collaborative effort between the Department of Water Resources and the local agencies (called Monitoring Entities) who are responsible for collecting and reporting the data; the Department’s role is to coordinate, maintain, and make the data available in a publicly-accessible database. The intent of the CASGEM program is to establish a permanent, locally-managed program of regular and systematic monitoring in all of California’s alluvial groundwater basins.

Accessing data about the state's groundwater basins
CASGEM basin prioritization
Basins subject to critical overdraft
Other sources of data on groundwater

Other Groundwater Topics

Conjunctive use

Conjunctive management refers to the planned use and management of both surface and groundwater resources to maximize the availability and reliability of water supplies in a region. With the right infrastructure in place, water districts and agencies can manage surface water and groundwater as a single source, using one to balance the other when surface water or groundwater levels are low, thus reducing diversions and groundwater pumping while enhancing supplies.

More information

Groundwater banking


Kern Water Bank

California has long relied on surface reservoirs to manage the state’s fluctuating water supply as evidenced by the over 1300 reservoirs both large and small that dot the landscape – from Redding in the north to San Diego in the south. However, environmental impacts, evaporation, and other concerns associated with reservoirs and the dams that create them have caused a shift towards groundwater banking as a water storage and management strategy for California.

The Central Valley, especially the southern portion of Kern County, is home to numerous groundwater banking operations which played a critical role during the dry years of 2007 to 2009, recovering over two-million acre-feet of banked supplies to their customers. However, groundwater banking is not just for the wide-open spaces of the Central Valley; when properly managed, the same techniques can be applied to groundwater basins in urban areas, providing a reliable local source of water.

How groundwater banking works
Kern Water Bank
Water Replenishment District of Southern California
Orange County Water District

Groundwater quality

Content coming soon.

Groundwater reports

Groundwater InformationLand subsidenceSGMA ImplementationGroundwater qualityOther topicsRegional Reports

California’s Groundwater Update 2013, special update to the California Water Plan, from the Department of Water Resources (2015)

Bulletin 118: California’s groundwater, from the Department of Water Resources (2003)

Addressing nitrate in California’s drinking water, from UC Davis and the State Water Board (2012)

Communities that rely on a contaminated groundwater source for drinking water, report to the legislature from the State Water Board

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