The Governor Edmund G. Brown California Aqueduct is a system of canals, tunnels, and pipelines that conveys water collected from the Sierra Nevada and valleys of Northern and Central California to Southern California. Named after California Governor Edmund Gerald "Pat" Brown Sr., the over aqueduct is the principal feature of the California State Water Project.

The aqueduct begins at the Clifton Court Forebay at the southwestern corner of the Sacramento–San Joaquin River Delta. The aqueduct then heads south, eventually splitting into three branches: the Coastal Branch, ending at Lake Cachuma in Santa Barbara County; the West Branch, conveying water to Castaic Lake in Los Angeles County; and the East Branch, connecting Silverwood Lake in San Bernardino County.

The Department of Water Resources (DWR) operates and maintains the California Aqueduct, including one pumped-storage hydroelectric plant, Gianelli Power Plant. Gianelli is located at the base of San Luis Dam, which forms San Luis Reservoir, the largest offstream reservoir in the United States.

The Castaic Power Plant, while similar and which is owned and operated by the Los Angeles Department of Water and Power, is located on the northern end of Castaic Lake, while Castaic Dam is located at the southern end.

Land subsidence has occurred along the aqueduct and has had a steady increase since its relatively stable state post construction of the aqueduct.

<!--==Geological context==

The Central Valley of California is surrounded by high mountains that are eroding into the valley itself. The valley is somewhat rebounding from recent ice age interglacial glaciations.

The region is prone to significant earthquakes due to the many faults and fault lines that pass through.

The flatness of the valley bottom contrasts with the rugged hills or gentle mountains that are typical of most of California's terrain. The valley is thought to have originated below sea level as an offshore area depressed by subduction of the Farallon Plate into a trench further offshore. The San Joaquin Fault is a notable seismic feature of the Central Valley.

thumb|right|An example of the extreme differences between the geology of the valley floor and that of the rugged hills of the Coast Ranges (Between Tracy and Patterson, CA:Interstate 5)

The valley was later enclosed by the uplift of the Coast Ranges, with its original outlet into Monterey Bay. Faulting moved the Coast Ranges, and a new outlet developed near what is now San Francisco Bay.

Over the millennia, the valley was filled by the sediments of these same ranges, as well as the rising Sierra Nevada to the east; that filling eventually created an extraordinary flatness just barely above sea level; before California's massive flood control and aqueduct system was built, the annual snow melt turned much of the valley into an inland sea.-->

The aqueduct system

thumb|San Luis Reservoir in July 2021

The aqueduct serves 35 million people and 5.7 million acres of farmland, and begins at the San Joaquin-Sacramento River Delta at the Banks Pumping Plant, which pumps from the Clifton Court Forebay. Water is pumped by the Banks Pumping Plant to the Bethany Reservoir. The reservoir serves as a forebay for the South Bay Aqueduct via the South Bay Pumping Plant. From the Bethany Reservoir, the aqueduct flows by gravity approximately to the O'Neill Forebay at the San Luis Reservoir. From the O'Neill Forebay, it flows approximately to the Dos Amigos Pumping Plant. After Dos Amigos, the aqueduct flows about to where the Coastal Branch splits from the "main line". The split is approximately south-southeast of Kettleman City. After the coastal branch, the line continues by gravity another to the Buena Vista Pumping Plant. From the Buena Vista, it flows approximately to the Teerink Pumping Plant. After Teerink it flows about to the Chrisman Pumping Plant. Chrisman is the last pumping plant before Edmonston Pumping Plant, which is from Chrisman. South of the plant the west branch splits off in a southwesterly direction to serve the Los Angeles Basin. At Edmonston Pumping Plant it is pumped over the Tehachapi Mountains.

Water flows through the aqueduct in a series of abrupt rises and gradual falls. The water flows down a long segment, built at a slight grade, and arrives at a pumping station powered by Path 66 or Path 15. The pumping station raises the water, where it again gradually flows downhill to the next station. However, where there are substantial drops, the water's potential energy is recaptured by hydroelectric plants. The initial pumping station fed by the Sacramento River Delta raises the water , while a series of pumps culminating at the Edmonston Pumping Plant raises the water over the Tehachapi Mountains.

A typical section has a concrete-lined channel at the base and an average water depth of about . The widest section of the aqueduct is and the deepest is . Channel capacity is and the largest pumping plant capacity at Dos Amigos is .

A 2021 study published in Nature Sustainability estimated that the installation of solar panels over the canal could potentially reduce annual water evaporation by of canal. While electricity generated by the solar panels could be used by the aqueduct's pumping systems, the study also considered the possibility of supplying power to irrigation systems in the Central Valley to reduce reliance on diesel-powered irrigation pumps. Similar canal-spanning solar installations have been demonstrated in India, including a steel truss design in Gujarat and a suspension cable design in Punjab.

Branches

From its beginning until its first branch, the aqueduct passes through parts of Contra Costa, Alameda, San Joaquin, Stanislaus, Merced, Fresno, and Kings counties. The aqueduct then divides into three branches: the Coastal Branch in the Central Valley, and the East and West Branches after passing over the Tehachapi Mountains.

thumb|right|Aqueduct and surrounding farms in [[Kern County]]

Coastal Branch

The Coastal Branch splits from the main line south-southeast of Kettleman City transiting Kings County, Kern County, San Luis Obispo County, and Santa Barbara County to deliver water to the coastal cities of San Luis Obispo, Santa Maria, and Santa Barbara. The Coastal Branch is and has five pump stations. Phase I, an above-ground aqueduct totaling from where it branches from the California Aqueduct, was completed in 1968. With construction beginning in 1994, Phase II consists of of a diameter buried pipeline extending from the Devils Den Pump Plant, and terminates at Tank 5 on Vandenberg Space Force Base in Santa Barbara County. The Central Coast Water Authority (CCWA) extension, completed in 1997, is a (30–39&nbsp;in) (76–99&nbsp;cm) diameter pipeline that travels from Vandenberg through Vandenberg Village, Lompoc, Buellton, and Solvang where it terminates at Lake Cachuma in Los Padres National Forest.

Coastal Branch facilities include:

  • Las Perillas Pumping Plant
  • Badger Hill Pumping Plant
  • Devil's Den Pumping Plant
  • Bluestone Pumping Plant
  • Polonio Pass Pumping Plant
  • Polonio Pass Water Treatment Plant
  • Cuesta Tunnel
  • Santa Ynez Pumping Facility In the San Joaquin Valley, the San Joaquin River flows roughly northwest for , picking up tributaries such as the Merced River, Tuolumne River, Stanislaus River and Mokelumne River.

In the south part of the San Joaquin Valley, the alluvial fan of the Kings River and another one from Coast Ranges streams have created a divide and resultantly the currently dry Tulare basin of the Central Valley, into which flow four major Sierra Nevada rivers, the Kings, Kaweah, Tule and Kern. This basin, usually endorheic, formerly filled during heavy snowmelt and spilled out into the San Joaquin River. Called Tulare Lake, it is usually dry nowadays because the rivers feeding it have been diverted for agricultural purposes.

The rivers of the Central Valley converge in the Sacramento-San Joaquin Delta, a complex network of marshy channels, distributaries and sloughs that wind around islands mainly used for agriculture. Here the freshwater of the rivers merges with tidewater, and eventually reach the Pacific Ocean after passing through Suisun Bay, San Pablo Bay, upper San Francisco Bay and finally the Golden Gate. Many of the islands now lie below sea level because of intensive agriculture, and have a high risk of flooding, which would cause salt water to rush back into the delta, especially when there is too little fresh water flowing in from the Valley.

The Sacramento River carries far more water than the San Joaquin, with an estimated of virgin annual runoff, as compared to the San Joaquin's approximately . Intensive agricultural and municipal water consumption has reduced the present rate of outflow to about for the Sacramento and for the San Joaquin; however, these figures still vary widely from year to year. Over 25 million people, living both in the valley and in other regions of the state, rely on the water carried by these rivers.

Land subsidence

Background

Land subsidence is when the land gradually or suddenly sinks or settles due to movement or removal of natural materials such as water, minerals, oil and natural gases. More often than not, subsidence occurs when large quantities of groundwater are removed from sediment or rocks. As groundwater is drawn from deep underground layers of clay, the clay compresses, causing subsidence. In cases of groundwater removal, disruption to land on the surface and underground water storage can either be elastic, meaning recoverable, or inelastic, meaning permanent. Coarse-grained sediment which holds groundwater can be drained and recharged with minimal underground and surface level damage and the change that does occur is considered seasonal subsidence. The aqueduct has been increasing in subsidence rates rapidly, even though it was relatively stable for many years after being constructed. The Tulare Basin is subsiding at a rate of about 30&nbsp;cm (one foot) per year, as measured by NASA's GRACE satellite. The Central Valley, where a large portion of the California Aqueduct runs through, has been affected by the pumping of groundwater and subsequent land subsidence. Farmers in and near the Central Valley have become reliant on groundwater especially with recent droughts impacting the amount of readily accessible surface water. From October 2011 to September 2015 measurements made on groundwater levels in the San Joaquin Valley's aquifers recorded a loss of 14&nbsp;km<sup>3</sup>/year, a total of 56&nbsp;km<sup>3</sup>.

Consequences

Subsidence can put land, both private and public, at risk of infrastructure damage. Bridges, levees, roads, and groundwater wells are either at risk of damage or have been damaged already. With subsidence progression, underground aquifers could be at risk and water storage from them could be threatened. was commissioned by the U.S. A&E network in the late 2000s. The documentary is typically shown on the History television channel in the United States, although other educational broadcasters globally have shown it. It features the Clifton Court Forebay (a primary intake point for California Aqueduct) as a "strategic piece of California freshwater infrastructure" subject to shutdown for up to two years if struck by an earthquake of magnitude 7.5 or greater.

The aqueduct is featured in an episode of California's Gold with Huell Howser.

See also

  • Colorado River Aqueduct
  • Los Angeles Aqueduct

References

  • The California Department of Water Resources website
  • Historic Pump-Storage Operation in WSCC
  • USGS Geographic Names Information System data