U.S. Department of the Interior Printed on recycled paper U.S. Geological Survey

Fact Sheet 2009–3040

May 2009

Science for 

Stewardship of 

California’s 

Water 

Resources

The USGS California 

Water Science Center brings many 

capabilities and tools to the understanding, 

management, and protection of California’s water 

and other natural resources. The Center’s approximately 

200 scientists and technicians are leaders in:

• Conducting long-term monitoring of streamflow and 

 water quality. 

• Developing new sampling, analytical, and interpretive

 methods to assess groundwater quality. 

• Studying the geology of groundwater systems to help 

 managers protect and optimize supplies.

• Devising new computer models that can play a key role

 in everything from managing surface-water and groundwater 

 supplies to assessing the impact of climate change on 

 individual watersheds.

• Conducting multi-disciplinary ecosystem and 

 watershed research, including large-scale 

 studies in the Sacramento-San Joaquin 

 River Delta and San 

 Francisco Bay.

Helping Agencies 

Manage 

and Protect 

Groundwater

USGS scientists are 

helping local water agencies throughout California 

better understand, manage, 

protect, and maximize the 

effective use of groundwater 

basins. Scientists are conducting 

water-quality assessments, developing groundwater computer models that 

simulate a variety of scenarios, and devising 

new strategies for replenishing groundwater basins 

and using them in conjunction with surface-water supplies. For 

instance, USGS scientists, 

working with the city of 

Victorville and the Mojave 

Water Agency, have found 

innovative new ways to 

recharge water through 

400 feet of dry earth in 

California’s Mojave Desert. 

Research could help the 

agencies use groundwater 

basins that were previously 

thought to be unavailable for municipal water 

storage. (http://ca.water.

usgs.gov/news/releaseMarch13_2008.html)

Maintaining a Long-Term Stream Monitoring Network

The USGS, in cooperation with State, local and Tribal 

agencies, operates more than 500 stream gages in California for 

monitoring of streamflow and water quality. This statewide network is part of a nationwide program that provides streamflow 

The U.S. Geological Survey (USGS) 

is the primary Federal 

agency responsible for 

scientific evaluation of 

the natural resources of 

the United States, including its water. To meet 

the demands of a growing 

California, the U.S. Geological Survey’s California Water 

Science Center provides essential 

science to help Federal, State, and 

local water agencies evaluate and manage California’s critical water resources; adapt 

to a changing climate; assess, predict, and mitigate 

natural hazards, such as mudslides and debris flows; and protect 

the health of rivers, forests, wetlands, and other habitats.

The following are some of the ways the USGS is working 

with other agencies to protect California’s water resources and 

assure that Californians have safe and reliable water supplies for 

now and in the future. 

Keeping Watch on Groundwater Quality

Groundwater provides more than 40 percent of California’s drinking water. To protect this vital resource, the State of 

California created the Groundwater Ambient Monitoring and 

Assessment (GAMA) Program. Under GAMA, the USGS is 

working with the State Water 

Resources Control Board to 

monitor and assess water quality in groundwater basins that 

are used for public supply. With 

the cooperation of local water 

agencies and well owners, the 

USGS is testing groundwater 

quality in those basins over a 

10-year period. (http://ca.water.

usgs.gov/gama/)

CALIFORNIA

WATER

SCIENCE

CENTER

Meg Hurst prepares water-quality 

samples in a mobile laboratory.

USGS geologist David O’Leary 

measures the depth to the water 

table at a pilot-study recharge pond 

near Yucca Valley.
resulted in a steady loss of land-surface elevation. As a result, 

most of the farmed Delta islands – such as Twitchell Island, 

above – are more than 20 feet below the surrounding waterways 

and must be permanently protected by levees. The USGS, 

working with the California Department of Water Resources 

and the University of California, is conducting research on 

a new type of farming that traps atmospheric carbon dioxide 

and rebuilds lost soils (http://ca.water.usgs.gov/news/ReleaseJuly23_2008.html).

Assessing Groundwater Availability in the 

Central Valley

Managing the Central Valley’s vast aquifer system – California’s biggest water reservoir – is an increasingly complex 

endeavor that is critical to the water supply of the entire State. 

The USGS has created a new water-modeling tool, the Central 

Valley Hydrologic Model, to help local water managers assess, 

understand, and address the myriad of issues affecting Central 

Valley groundwater supplies. The model could be used by 

managers to: 

• Effectively manage the interdependent use of surface

water and groundwater.

• Conserve farmland.

• Assess the effect of land-use changes on water 

resources.

• Assess the effects of climate change on groundwater 

supplies.

information for a variety of purposes, including drought and 

flood monitoring. It also provides long-term data to detect 

changes in streamflow caused by human activities or climate 

change. USGS streamflow gaging stations equipped with realtime telemetry are integral components of reservoir operations and river-forecast and flood-warning systems. Real-time 

streamflow information is available online at http://waterdata.

usgs.gov/nwis/rt.

Understanding the California Delta

The Sacramento-San Joaquin River Delta is the hub of 

California’s water system and also an imperiled habitat for 

fish and other wildlife. The USGS California Water Science 

Center is working with several Federal, State, and local agencies to develop the science for addressing a number of Delta 

issues. These issues range from fish migration and water flow 

to pesticides, water quality, and land-surface subsidence. In one 

of the largest projects, USGS scientists are conducting a hightech study in cooperation with the California Department of 

Water Resources to gather data on route selection and survival 

of juvenile salmon as they make their way through the Delta 

to the ocean. This research involves many scientific disciplines 

and the use of emerging technologies in fisheries science and 

hydrodynamic measurement, including a remote-controlled boat 

(below) that gathers data on river flows (http://ca.water.usgs.

gov/news/ReleaseNov14_2008.pdf). 

Planning for Climate Change

A changing climate will have profound and wide-ranging 

impacts across California. Water and environmental-resource 

managers need new scientific tools that will help them predict 

how a changing climate will affect local watersheds, groundwater basins, forests, and wetlands. USGS scientists are 

developing those tools. Using their knowledge of hydrology and 

physical processes, scientists are able to create a link between 

future climate scenarios and what may happen to ecosystems 

and water supplies.

The USGS is also developing a pilot project to potentially 

reverse, or minimize, one of the causes of global warming – the 

emission of greenhouse gases to the atmosphere. The project 

might also help save one of California’s most-imperiled landscapes – the Sacramento-San Joaquin River Delta. Throughout 

the Delta, oxidation of the soils from farming practices has 

Scientists release tagged 

juvenile salmon into the 

California Delta. A remotecontrolled boat gathers 

stream data. 

A test “carbon-capture” farm 

shows promise for making 

Delta islands less vulnerable 

to flooding.
Detail of model grid

Pacific Ocean

Central Valley

Model Grid 

Boundary

California Department 

of Water Resources

water balance subregions

A

A'

San

Francisco

Central

Valley

C A L I F

O

R

N I A

flooding or debris flows during heavy rainfall. The webcams 

provide visual data to the National Weather Service, firstresponders, and area residents of real-time conditions in creek 

channels. The webcams, which can be viewed and operated 

remotely by the public, can be accessed at http://ca.water.usgs.

gov/webcams/.

Central Valley Hydrologic Model

Cross section 

Land surface

Layer 10

Layer 9

Layer 8

Layer 7

Layer 6 Layer 3

Layer 2 Layer 1

Corcoran Clay

Not in model

A A'

0 57 miles DISTANCE ALONG SECTION

ALTITUDE, IN FEET -2,500

Sea 

Level

1,000

This new tool simultaneously accounts for changing water 

supply and demand. It simulates irrigated agriculture and surface-water and groundwater flow across the entire Central Valley hydrologic system. The detail and breadth of this hydrologic 

model makes it invaluable to water-resource managers faced 

with increasing water-management challenges and constraints.

Real-Time Monitoring of Hydrologic Hazards

The USGS California Water Science Center has installed 

a network of webcams across California in conjunction with 

its stream gages. Several of the webcams are in watersheds 

in Santa Barbara, Ventura, Orange, Los Angeles, and San 

Diego Counties that, because of recent fires, are at high risk of 

To create enough detail 

to be useful for watermanagement decisions 

for the entire Central 

Valley aquifer system, 

an extensive threedimensional computer 

model was designed. 

The aquifer was divided 

horizontally into 20,000 

model cells of 1 square 

mile, and vertically into ten 

layers ranging in thickness 

from 50 to 1,800 feet. 
For 

more information on 

the California Water Science 

Center, visit our Web site at http://

ca.water.usgs.gov/ or call the Sacramento 

Project Office at (916) 278-3000 or the San 

Diego Project Office at (619) 225-6100.

Contacts:

• Eric Reichard, Acting Director

(egreich@usgs.gov)

• Donna Schiffer, Deputy Director

(schiffer@usgs.gov)

•James Nickles,

Public Affairs Specialist

(jnickles@usgs.gov)

Assessing the Fate and Transport of Pesticides 

The USGS Pesticide Fate Research project is a series of 

studies that assess the occurrence, transport, and fate of currentuse pesticides in water throughout California, including the San 

Francisco Bay watershed, the Salton Sea, and central California 

coastal rivers. Working with toxicologists and ecologists, USGS 

scientists are focusing on the potential effects of compounds on 

aquatic organisms and human health. Scientists have developed 

analytical methods for measuring pesticide concentrations in 

water, sediments, and biological tissues at environmentally relevant levels. They are conducting field studies to track when and 

where these pesticides occur in waterways. Complementary 

laboratory studies are also under way to understand the factors 

controlling the breakdown rates of pesticides in the environment. (http://ca.water.usgs.gov/user_projects/toxics/)

Measuring Land Subsidence

The USGS is studying land subsidence in several regions, 

including the Coachella Valley in Southern California. Since 

the 1920s, groundwater has been a major source of agricultural, 

municipal, and domestic supply in the valley. Overpumping has 

caused underground water tables to drop as much as 100 feet. 

That has led to declining land-surface elevations, known as 

subsidence, which can disrupt surface drainage; reduce aquifer 

storage; cause earth fissures; and damage wells, buildings, roads 

and utility infrastructure. The USGS and the Coachella Valley 

Water District launched the research in 1996. USGS scientists 

are using Global Positioning System (GPS) surveying and a 

satellite mapping process known as Interferometric Synthetic 

Aperture Radar (InSAR) to document the drops in elevation. 

The data collected are helping the Coachella Valley Water District develop new water-conservation and management initiatives to eliminate overpumping. (http://ca.water.usgs.gov/news/

release071217.html)

 

CALIFORNIA

 WATER

 SCIENCE

CENTER

USGS researcher Kelly Smalling gathers fish-tissue samples for a 

pesticide study on California’s Central Coast. 

The USGS uses a Global Positioning System (GPS) to measure 

changes in the position of Earth’s surface (subsidence) over time at 

20 bench marks in the Coachella Valley.