Groundwater

California's groundwater resources are nearly as important as its rivers in terms of supply, and have been perhaps even more important economically.

Current supplies of useable groundwater in California are estimated to be six times the volume of all the state's surface water reservoirs combined. About half the population in California relies on groundwater for drinking.

Read Groundwater — California's Hidden Resource.

Groundwater is water that resides beneath the ground surface, in small spaces around soil or rock particles. The water got there by draining through surface layers of soil and rock, and the groundwater may in turn seep out to join streams and rivers. Thus groundwater and surface water are linked in the hydrologic cycle. Typically, streams contribute to the recharging of groundwater supplies in the spring, when runoff is high. In the fall, stream flow may be fed by the groundwater.

Groundwater sources may be found below the surface in most of the state, particularly along the Central Valley and underlying the Colorado Desert. In some cases the groundwater is under pressure, so that it rises to the surface without the aid of pumps when wells are dug. Such wells are called flowing artesian wells. In other cases, electric or wind-driven pumps may be used to bring the water to the surface.

Typically, about 30 percent of urban and agricultural water use is groundwater, but in dry years and in some areas, it may be 60 percent.

Facts and diagrams about groundwater.

Lakes and reservoirs

Besides its many rivers, northern California boasts sources of fresh water in mountain lakes, such as Lake Tahoe in the Sierra Nevada range, and in reservoirs, such as Lake Shasta — the largest reservoir in California — near Redding.

Until the end of the 19th century, California's Central Valley boasted the largest freshwater lake west of the Mississippi, Tulare Lake (pronounced tooLAIRee). At its largest, Tulare Lake probably covered 760 square miles (four times the size of Lake Tahoe). It was a rich source of freshwater fish, turtles, and frogs, many of which were consumed in the restaurants of San Francisco. The lake was drained for farmland during the mid-1800s.

Lake Tahoe. Source: Wikipedia

Modifications to California's freshwater sources

Centuries-old irrigation ditches built by Native Americans are known in some areas, such as those built by ancestors of the Agua Caliente Cahuilla Indians near Palm Springs.

In the 18th century, Spanish settlers, in conjunction with building California's missions, built larger scale irrigation systems that supplied river water for drinking and bathing, for irrigating orchards, vineyards and vegetable crops, and for driving mills to grind wheat.

Washbasin at Mission Santa Barbara, built about 1806.
Source: Wikipedia

Hydraulic mining

Major modifications of California's freshwater sources began with the discovery of gold on the western slope of the Sierra Nevada, in 1848. Early prospectors looked for gold by agitating ore and stream water in a pan and watching for the heavier gold particles to separate from sand and mud and settle at the bottom of the pan. By the mid-1850s, however, more water-intensive methods of extracting gold were used.

Hydraulic mining involved aiming high-pressure water hoses at the side of the mountain to clear away topsoil, and filtering out the gold from the gravel and debris that washed down. This technique was very destructive environmentally.

Sand, silt, and gravel from the mines clogged the Sacramento and other rivers, causing damaging floods and making navigation by steamboat nearly impossible. Farmers whose land had been ruined began seeking redress from the courts. In 1884, a judge from the US 9th Circuit Court issued an injunction against all hydraulic mining in the state.

See historic photos of hydraulic gold mining.

Exploitation of groundwater

The farmers' victory over the miners in the case of hydraulic mining highlights the increasing importance of agriculture in California, which became a state in 1850. The first farmers practiced dryland farming (without irrigation) and grew mostly wheat and barley. But in the 1850s, farmers in the Central Valley began tapping into groundwater sources.

Sometimes the water existed underground at high pressure and rose to the surface on its own, in what is called an artesian well; in other cases windmills pumped the water to the surface. By 1865, many farmers had switched from dryland farming to irrigated agriculture.

The completion of the transcontinental railway in 1869 prompted some of this intensive use of groundwater. The availability of refrigerated rail cars meant that farmers in California had an incentive to grow water-intensive but lucrative fruit and other crops for winter consumption in the east.

Subsidence

One potential problem with intensive use of groundwater is subsidence (sinking) of the land as water is removed from underground aquifers — and even after the water is no longer actively drawn out. In the San Joaquin Valley, more than 5,000 square miles of valley floor sank by at least a foot between 1925 and 1977. In an area west of Mendota, the subsidence amounted to 30 feet!

Learn more about subsidence.

Dr. Joseph Poland of the United States Geological Survey, standing by a pole that shows land levels in 1925, 1955, and 1977. In 1925, the ground surface was at the marker at the top of the pole. The subsidence was due to groundwater extraction. Source: US Geological Survey

Data for the Santa Clara Valley (a part of the Central Valley just south of the San Francisco Bay area) provides an example of the rapid increase in groundwater use: The first well was dug in the early 1850s; by 1865, there were about 500 artesian wells. In 1920, two-thirds of the valley was irrigated, and farmers were drilling 1,700 new wells each year. By 1930, water no longer rose to the surface on its own, as the water table was 80 feet below the ground surface. Industrial users of fresh water moved in, and by 1960 were using twice as much water as farmers. In 1964, the water table was 235 feet below ground level.

Read the complete story of Santa Clara's water here.

Subsidence in the Santa Clara Valley as of 1962. Source: Poland, J. F. and Ireland, R. L, USGS

Groundwater contamination

Another problem with the use of groundwater today is its potential contamination with hazardous chemicals.

Until the 1970s, it was thought that soil would filter agricultural and industrial byproducts from water as it percolated down to underground aquifers. However, groundwater in some places is now known to be contaminated with pesticides, chemicals such as perchlorate from defense-related industrial plants, solvents from computer makers and benzene from leaky gas storage tanks. Other sources of groundwater contamination include landfills, leaking septic systems, de-icing salts used on roads, and hazardous waste sites.

It is difficult to assess the extent of the problem in California. Remediation of contaminated groundwater sites is possible (for example, by removing soil and pumping and treating the water) but expensive. Prevention of contamination is critical.

In recent decades, substantial progress has been made in artificially recharging groundwater supplies to use them as underground reservoirs.

Reclamation of wetlands

The federal government, through a series of legislative acts between the 1850s and 1970s, encouraged the draining of swampland and the reclamation of wetlands for farming and for the elimination of mosquito breeding grounds. In California, this led to intensive efforts in the 1860s to build levees and drains, particularly along the Sacramento River and in the Delta. By the 1920s, an estimated 70 percent of wetland acreage had already been modified by drainage and reclamation efforts.

Read the section on 1900 to 1950 for more details.

The situation changed in the 1970s, when policy setters became convinced of the important environmental functions of wetlands. These include reducing flood peaks by detaining storm flows, protecting coastal areas from wave erosion, and recharge groundwater supplies. The protection and restoration of some wetlands is now legislatively encouraged.

Diversion of water for urban centers

As agricultural use of water in California rose beginning in the 1850s, urban centers grew too, creating a larger demand for municipal water. Small towns located along rail routes began to grow in the Central Valley, and Los Angeles and San Francisco saw big gains in population around the turn of the century and in the early years of the 20th century.

In 1880, the population of Los Angeles was 11,000. A decade later it was 60,000. In 1900, it was about 100,000. By 1921, 1 million people lived in Los Angeles County.
San Francisco already had a population of 233,000 in 1880, and this reached about 500,000 in 1920.

Learn more about the population history of San Francisco and Los Angeles.

The increase in urban population led city leaders to initiate projects to assure the supply of fresh water and electricity from hydropower. San Francisco and Los Angeles naturally account for two of the largest such locally controlled projects.

Perhaps the most famously controversial dam in the United States is the one San Francisco built on the Tuolumne River in the Hetch Hetchy Valley of the Sierra Nevada to supply the city with fresh water.

The O'Shaughnessy Dam was completed in 1923. (Downstream from this dam are the Kirkwood, Moccasin, and Holm hydropower facilities.) John Muir and other early environmentalists vigorously opposed the plan to flood the Yosemite Valley. Environmental groups are currently arguing for the removal of the dam.

Read basic information on Hetch Hetchy from the Bay Area Water Supply and Conservation Agency, which represents cities, water districts, and private utilities.
Learn about current environmental proposals to restore the Hetch Hetchy Valley.

Hetch Hetchy Reservoir in Yosemite National Park. Source: Wikipedia

Los Angeles' acquisition of Owens Valley River water was also highly controversial.

In 1902, Fred Eaton, an engineer and former mayor of Los Angeles, created the Los Angeles Department of Water and Power (now the nation's largest municipal utility). Eaton and his associate William Mulholland began buying land and water rights in Owens Valley in 1905. Owens Valley residents were under the impression they were selling land and water rights for a federal irrigation project, and were outraged to find out later that the water was for the city of Los Angeles. The first aqueduct bringing water from Owens Valley to Los Angeles, which was completed in 1913, is the Los Angeles Aqueduct (although it is sometimes referred to as the Owens Valley aqueduct). Some aspects of this story inspired the 1974 film Chinatown.

Two Caterpillar 45 steam tractors pull a wagon train in the Mojave Desert during construction of the Los Angeles Aqueduct in 1909. Source: Wikipedia

Mono Lake was partially drained by a 1941 extension of the Los Angeles Aqueduct and became a battleground in the so-called California water wars.

Other water transport and storage projects built to provide cities with drinking water include the Colorado River Aqueduct (built between 1933 and 1941, to serve southern California) and the first Mokelumne Aqueduct (completed in 1929, to serve the eastern side of the San Francisco Bay Area).

Of course, California’s population continued to grow, and did so at a fantastic rate after World War II. The influx of workers who found jobs in the defense and computer industries contributed to a steep rise in both industrial and municipal water use.

The Central Valley Project

Army engineers first contemplated a comprehensive approach to irrigating the Central Valley for agricultural use in 1873. Federal and state agencies then contributed to the unfolding plan, and in 1931 the state's Division of Water Resources presented a comprehensive proposal to the state legislature.

The plan called for the state to sell revenue bonds to finance the construction of facilities for the storage and transport of water in the Central Valley, but the Great Depression impeded the sale of those bonds. The federal government took control of the project, which is now operated by the U.S. Bureau of Reclamation. Construction of the project's various dams and canals began in 1937.

Although the original purpose of the Central Valley Project was to provide for irrigation of Central Valley farmland, it now includes facilities to generate power and to improve flood control and navigation, projects to enhance water quality and provide for recreation, and measures to restore fish and wildlife habitats. The Central Valley Project involves 20 dams and reservoirs, 11 power plants, and some 500 miles of canals. It is a vital source of water for three-quarters of the irrigated land in California.

Learn more about the Central Valley Project and its history.

Shasta Dam, on the Sacramento River above Redding, is shown here under construction in June 1942. Source: Wikipedia

The State Water Plan and the California Aqueduct

The State Water Project (SWP) — the largest state-built water project in the nation — is a complex array of dams, power plants, canals, and pumping stations. It provides millions of acre-feet of water per year from the Sacramento Delta to communities north and south of the Bay Area and in San Luis Obispo and Santa Barbara counties. About half the water is pumped south to San Joaquin Valley farms and over the Tehachapi Mountains to urban areas of Southern California. (Such pumping of water around the desert southwest leads to jokes about water flowing uphill towards money!)

In the middle of the SWP's chain of canals, reservoirs, and pumps are facilities that are shared with the federal Central Valley Project. The California Department of Water Resources, which operates the SWP, works closely with the U.S. Bureau of Reclamation, which operates the Central Valley Project, to run the combined systems. (The SWP was built most intensively between 1961 and 1974.)

Lake Palmdale, with the California Acqueduct in the foreground. Source: Wikipedia

To cross the Tehachapi Mountains, the SWP raises the level of water nearly 2,000 feet — “more water pumped higher than anywhere else in the world,” according to Sue McClurg in Water and the Shaping of California.

South of the Tehachapi mountains the water flows into two main aqueduct branches, one going east and the other west, and connects to lines of the Metropolitan Water District of Southern California and other contracting agencies. (Entire books have been written about the major water agencies and projects in California! The State Water Project alone supplies water to 29 agencies.)

The 444-mile long California Aqueduct is a prominent aspect of the State Water Project.

Salt in soil and water

All over the world, the irrigation of crops in arid and semi-arid regions leads eventually to an accumulation and concentration of mineral salts in the soil and in the water that drains from agricultural land. In what is known as the Fertile Crescent in ancient Mesopotamia, farmers were gradually forced to switch from growing wheat to growing only more salt-tolerant barley over a period of 2,000. More recently, in Egypt, farmers saw crop deterioration as a result of salt buildup in only five years.

Learn more about the problem of salt buildup in general, and its effect on Mesopotamia.

The concentration of salts in the soil and in agricultural runoff occurs when there is insufficient drainage. Salt that is naturally present in the soil or in the irrigation water gets left behind on the surface of the ground or in the root zone when water evaporates or is transpired by plants. To avoid the buildup of salts, farmers must be able to supply extra water to flush the salts away. The salts generally end up in the groundwater (which may also create a problem).

Salts dissolved from the soil on rangeland in Colorado. Source: Wikipedia

In California, the buildup of some specific salts came to the public’s attention in the early 1980s, when migratory waterfowl and fish in Kesterson Reservoir in the San Joaquin Valley began to sicken, die, or disappear. Farmers were also reporting the deformity or death of livestock. An investigation by state and federal researchers revealed that agricultural drainage water directed into the reservoir was very high in selenium salts, which occur naturally in the soil on the western side of the valley. Although selenium in low doses is vital to life, at sufficiently high levels, selenium is toxic to wildlife and humans.

Remediation of the Kesterson Reservoir area began immediately, and environmental agencies and academic researchers began studying the newly named Kesterson effect to see how it can be avoided. The U.S. Bureau of Reclamation is studying options to address drainage issues in the San Joaquin Valley and keep selenium out of the food chain. State officials now see the problem as one of preserving the sustainability of agriculture in the Central Valley; the California Health and Safety Code declares that “the buildup of salt and selenium in agricultural soil is an unsustainable practice that degrades soil, harms an irreplaceable natural resource, reduces crop yields and farm income, and poses threats to wildlife.”

Read a fact sheet on the salt balance problem.
For all the details, read an overview of the entire problem and proposed solutions from an academic research perspective.