5.2: Sources for Californias Water

California's limited water supply comes from two main sources: surface water, or water that travels or gathers on the ground, like rivers, streams, and lakes; and groundwater, which is water that is pumped out from the ground. The primary contributor for these sources is rainfall and California’s snowpack. Because both surficial and ground water are becoming either unreliable or depleted, California has had to begin producing a small amount of desalinated water, water that was once sea water, but has been purified. As an example, Catalina Island’s water comes from combination of underground aquifers and a desalination plant. While that plant helps supplement the lack of natural water supply, Catalina is still unable to meet the annual water needs of the island – making a steady supply of rain essential.

Figure 5.2: A Map of Water Storage, Watersheds, Rivers, & Delivery Facilities.[1]

Ground Water

Groundwater is a critical component for California’s water supply. During a normal year, 30% of the state's water supply originates from groundwater (underground water). In times of intense drought, groundwater consumption can rise to 60% or more. Over 850,000,000 acre-feet (276,973,717,105,760 gallons) of water is stored in California's 450 known groundwater reservoirs; however, not all the water is usable. California's water situation presents a complex challenge. Groundwater, despite its wider distribution compared to surface water concentrated in the north, faces significant limitations. Firstly, over half is unusable due to poor quality, potentially from natural minerals or accumulated pollutants. Secondly, centuries of rapid extraction have caused saltwater intrusion, contaminating remaining water with salt, and making it unsuitable for many uses. Finally, pumping groundwater, especially from deeper wells, can be expensive due to the high energy demands. These limitations highlight the need for a balanced approach to water management in California.

The largest groundwater reservoirs are found in the Central Valley. The majority of the supply there is in the form of runoff that seeps into the aquifer. Freshwater is usually found in deposits of gravel, silt, and sand. Below these deposits lies a layer of deep sediment, a relic of the era when the Pacific Ocean covered the area.

The large quantity of water beneath the surface has given rise to the misconception that groundwater is a sort of renewable resource that can be limitlessly tapped. Calculations assuming that groundwater usage is sustainable if the rate of removal equals the rate of recharge are often incorrect because of ignoring changes in water consumption and water renewal.

While the volume of groundwater in California is very large, aquifers can be over drafted when groundwater is removed more rapidly than it is replenished. Overdraft occurs where the average annual amount of groundwater extraction exceeds the long-term average annual supply of water to the basin. Effects of overdraft can include seawater intrusion, land subsidence, groundwater depletion, and/or chronic lowering of groundwater levels. In 1999, it was estimated that the average annual overdrafting was around 2,200,000 acre-feet (716,873,150,156 gallons) across the state, with 800,000 acre-feet (260,681,145,511 gallons) in the Central Valley. Since 1999, overdrafting has significantly increased, causing further strain and concern for California’s water storage. Satellite measurements found that in just the combined Sacramento and San Joaquin River basins, including the Central Valley, overdrafting between 2011 and 2014 was 12,000,000 acre-feet (3,910,217,182,669 gallons) of water per year… that is nearly 4 trillion gallons of water.

Groundwater-related subsidence is the subsidence (or the sinking) of land resulting from groundwater extraction. It is a growing problem in the developing world as cities increase in population and water use, without adequate pumping regulation and enforcement. One estimate has 80% of serious U.S. land subsidence problems associated with the excessive extraction of groundwater, making it a growing problem throughout the world.

Groundwater can be considered one of the last free resources, as anyone who can afford to drill can usually draw up merely according to their ability to pump (depending on local regulations). However, as seen in the figure, pumping-induced drawdown causes a depression of the groundwater surface around the production well. This can ultimately affect a large region by making it more difficult and expensive to pump the deeper water. Thus, the extraction of groundwater becomes a tragedy of the commons, with resulting economic consequences.

Figure 5.2: An Image of Maximum Subsidence in the San Joaquin Valley from 1925 to 1977.[2]

The arid areas of the world are requiring more and more water for growing populations and agriculture. In the San Joaquin Valley of California, groundwater pumping for crops has occurred for generations. This has resulted in the entire valley sinking an extraordinary amount, as much as 28 feet, as shown in figure 5.2. This has not come without consequences. Any large-scale change of topography, no matter how slight it may seem, has the potential to drastically change the surface-water hydrology. This has happened in the Joaquin Valley and other regions of the world, such as New Orleans and Bangkok.

Surficial Water

California has ten major drainage basins defined for convenience of water management. These basins are divided from one another by the crests of mountains. From north to south the basins are: North Coast, Sacramento River, North Lahontan, San Francisco Bay, San Joaquin River, Central Coast, Tulare Lake, South Lahontan, South Coast, and Colorado River regions. Each region incorporates watersheds from many rivers of similar clime. Many of the drainage basins are extremely altered, with hydroelectric power generation happening in much of the upper portion of these watersheds.

Figure 5.2: A Map of Major Rivers in California.[3]

The Central Valley watershed, which incorporates the Sacramento River, San Joaquin River, and Tulare Lake regions, is the largest in California, draining over a third of the state – 60,000 square miles (160,000 km2) – and producing nearly half the total runoff. The Sierra Nevada snowpack feeds Central Valley River systems and is a critical source of water in the state's long dry season when little if any precipitation falls. Up to 30 percent of California's water supply is from snowpack, and most of the California's hydroelectricity is also generated from the Sierra Nevada snowpack. More generally, in the US one of the largest uses of fresh water is withdrawal for the energy sector. Much of California's extensive reservoir and aqueduct system is designed to store and capture runoff from the Central Valley watershed. As this infrastructure ages, dam removal in California has become more widespread—a process that has been largely successful. The Sacramento and San Joaquin Rivers converge at the Sacramento–San Joaquin River Delta, a large fresh-water estuary where much of the state's water supply is withdrawn. The Central Valley watershed provides most of the water for Northern and Central California, as well as a significant chunk of Southern California's usage.

A proposed project by the Project Authority aims to divert water from the Sacramento River, upstream of the Delta, for storage in a new reservoir located 14 miles away. Existing canals would be used to transport the water. Construction is tentatively scheduled to begin in mid-2024, with operations targeted to start by 2030. The estimated cost of $3.9 billion would be funded through a combination of local, state, and federal public money. Significantly, the project has already secured funding from California's Proposition 1 water bond ($816 million) and the U.S. Department of Agriculture ($449 million). The U.S. Bureau of Reclamation is also a key partner.

The new reservoir would be incorporated into the existing California State Water Project (SWP). While economic benefits are estimated around $260 million annually, operation costs are projected to be between $10 million and $20 million. Based on a "beneficiary pays" principle, approximately 30 public water agencies, irrigation districts, counties, and cities in California have expressed tentative financial commitment to the project.

The North Coast watershed receives the highest annual precipitation of any California watershed. It incorporates many large river systems such as the Klamath, Smith, Trinity, and Eel, and produces over a third of the runoff in the state. With the notable exceptions of the Trinity Dam complex that transfers water from the Trinity River into the Sacramento River and Scott Dam that transfers water from the Eel River into the Russian River, most of the North Coast watersheds are relatively undeveloped, some have federal Wild and Scenic status that protect them from development; the northern coastal rivers provide water for salmonid habitat, carbon-sequestering forests, and local communities; some are within the influence of tribal water and fishing rights. Water flowing in these watersheds and into the Pacific Ocean is critical for sensitive, threatened, and endangered salmonids. There have been proposals to create additional inter-basin transfers from North Coast rivers to increase water supplies in the rest of California, but these projects have been rejected due to presumed environmental harm.

The Colorado River originates more than 1,000 miles (1,600 km) from California in the Rocky Mountains of Colorado and Wyoming and forms the state's southeastern border in the Mojave Desert. Unlike the other California watersheds, essentially all the water flowing in the Colorado River originates outside the state. The Colorado River is a critical source of irrigation and urban water for southern California, providing between 55 and 65 percent of the total supply.

The Central and South Coast watersheds include the most populous regions of California – the San Francisco Bay Area, Los Angeles, and San Diego – but have relatively little natural runoff, requiring the importation of water from other parts of the state.

Rivers of the Lahontan watersheds in eastern California are part of the high desert Great Basin and do not drain to the Pacific. Most of the water is used locally in eastern California and western Nevada for irrigation. The Owens River of the South Lahontan region, however, is a principal source of water for Los Angeles.

Figure 5.3: California’s Main Watersheds. [4]

Table 5.1: 10 Main California Watersheds

Hydrologic Region	Annual Precipitation	Annual Runoff
North Coast	55,900,000 acre-feet (69.0 km^3)	28,900,000 acre-feet (35.6 km^3)
Sacramento River	52,400,000 acre-feet (64.6 km^3)	22,400,000 acre-feet (27.6 km^3)
North Lahontan	6,000,000 acre-feet (7.4 km^3)	1,900,000 acre-feet (2.3 km^3)
San Francisco Bay	5,500,000 acre-feet (6.8 km^3)	1,200,000 acre-feet (1.5 km^3)
San Joaquin River	21,800,000 acre-feet (26.9 km^3)	7,900,000 acre-feet (9.7 km^3)
Central Coast	12,300,000 acre-feet (15.2 km^3)	2,500,000 acre-feet (3.1 km^3)
Tulare Lake	13,900,000 acre-feet (17.1 km^3)	3,300,000 acre-feet (4.1 km^3)
South Lahontan	9,300,000 acre-feet (11.5 km^3)	1,300,000 acre-feet (1.6 km^3)
South Coast	10,800,000 acre-feet (13.3 km^3)	1,200,000 acre-feet (1.5 km^3)
Colorado River	4,300,000 acre-feet (5.3 km^3)	200,000 acre-feet (0.25 km^3)

Figure 5.4: California’s Main Watersheds & Annual Precipitation/Runoff Rates. [5]

Rain & Snowfall

Rain typically falls in California mostly during the winter and spring months, from October through May, with more rain falling on the northern half of the state than the southern. Approximately 75 percent of the total precipitation volume occurs north of Sacramento, while 75 percent of the total water demand is in the south. With very rare exceptions, summers are dry throughout the state. Precipitation falling as snow in the Sierra and other mountain ranges feeds the network of reservoirs and surface water sources that supply the state; a low rainfall or light snowfall year can result in drought.

Rivers in northern and coastal California are mainly rain fed, peaking from January to April and falling to very low levels between June and November. Snowmelt has a significant influence on the Sierra Nevada rivers from east of Sacramento to east of Bakersfield, which typically peak between April and July. Snowmelt is also the primary water source for the Colorado River which supplies southern California.

Annual precipitation in California is highly variable, with a statewide average of 22.9 inches (58.2 cm) of precipitation per year. However, recorded precipitation totals can fluctuate heavily from year to year because of atmospheric conditions and climate change. El Niño–Southern Oscillation often has a significant effect on the state's precipitation, with generally higher precipitation during El Niño periods. In addition, climate change has impacted California's precipitation patterns in recent years with effects including more rapid snowmelt, more frequent heatwaves, and drier conditions across the state. California precipitation and snowpack are measured by the state of California by "water year", which runs from October 1 to September 30.

From late 2022 through spring 2024, California experienced a relentless barrage of atmospheric rivers. These concentrated bands of moisture in the atmosphere unleashed record-breaking rainfall, causing widespread problems. Excessive rain overwhelmed rivers and streams, triggering extensive flooding in the Central Valley, Salinas Valley, and the Santa Cruz Mountains.

Desalinization

In response to water shortages in the state, some water districts are looking to desalination to provide water for residents. Supporters view seawater desalination as a more reliable water source, since it draws its water from the ocean and thus, is not affected by periods of drought like other sources of water are. Another incentive for desalination is the ability for localities to be more self-sufficient with their water supply, thus improving their drought resilience. However, desalination has been the subject of scrutiny by opponents, who believe that the costs and possible environmental effects of desalination are indicators that California should continue to pursue other alternatives.

Below is a photo of the desalination plants on Catalina Island, which produce 40% of the island’s drinking water.

Figure 5.5: Catalina Islands Desalinization Plant. Photo by Jeremy Patrich is licensed under CC BY 4.0

Although the response to desalination has been mixed, some areas of California are moving forward with seawater desalination. As an example, in December 2015, Poseidon Water completed the construction of the Claude "Bud" Lewis Carlsbad Desalination Plant, in Carlsbad California. This facility, which was approved by the San Diego Water Authority, is responsible for providing water for about 8% of San Diego County's water by the year 2020. The facility cost $1 billion to build and is the largest desalination facility in the Western Hemisphere producing up to 50 million gallons (190,000 m3) of water per day. This plans also uses approximately 35 megawatts (MW) to produce 50 million gallons of water per day. This translates to roughly 246,156 megawatt hours (MWh) of electricity used per year. As of December 2015, there are 6 additional seawater desalination plants currently in operation in the state of California. As of 2022, there are 12 active desalination plants.

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[1] Image by Wikimedia is licensed under a CC-BY-SA 4.0 license.

[2] Image by Wikimedia is licensed under a CC-BY-SA 4.0 license.

[3] Image by Wikimedia is licensed under a CC-BY-SA 4.0 license.

[4] Graphic by Jeremy Patrich

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