Sacramento–San Joaquin River Delta

The Delta consists of approximately 57 reclaimed islands and tracts but there are nearly 200 islands in the delta that are named or not named. These are all surrounded by of levees that border of waterways. The southwestern side of the Delta lies at the foothills of the California Coast Ranges, while to the northwest sit the lower Montezuma Hills. Most of the Delta lies within Contra Costa, Sacramento, San Joaquin, Solano and Yolo Counties. The total human population of the Delta was 515,264 as of 2000. The main source rivers include the Sacramento River from the north, the San Joaquin from the southeast, and the Calaveras and Mokelumne Rivers from the east. The Calaveras and Mokelumne are both tributaries of the San Joaquin River. The Sacramento and San Joaquin Rivers join at the western end of the Delta near Pittsburg, at the head of Suisun Bay, although they are linked upstream by the Georgiana Slough, which was first used by steamboats in the 19th century as a shortcut between Sacramento and Stockton. The southwestern part of the Delta is also transected by the Middle River and Old River, former channels of the San Joaquin. These rivers transport more than of water through the Delta each year – about 50 percent of all California's runoff. Nearby cities include Lodi and Stockton to the east, Tracy and Manteca to the south, Brentwood to the southwest, and Pittsburg and Antioch to the west. The state capital, Sacramento, is located just to the north of the Delta. The Sacramento River Deep Water Ship Channel connects the Delta to the Port of Sacramento, with its terminus located near Rio Vista, on the northwestern side of the Delta. The Stockton Ship Channel is a dredged and partially straightened section of the San Joaquin River cutting directly through the Delta from the Port of Stockton to the San Joaquin's confluence with the Sacramento near Antioch. ==Geology, formation and natural conditions==

The Delta was formerly located at the bottom of a large inland sea in the Central Valley, which formed as the uplift of the California Coast Ranges blocked off drainage from the Sierra Nevada to the Pacific. About 560,000 years ago, water breached the mountains, carving out the present-day Carquinez Strait and San Francisco Bay. The drainage of all the water through this narrow gap formed a bottleneck in the Central Valley's outflow; this constriction is essential to provoke the slowing of river current and the resulting sediment deposits that now make up the Delta. The Delta in its contemporary (pre-1850s) state began to form about 10,000 years ago at the end of the last Ice Age. During the Ice Age global sea levels were about lower than today, and the Delta region, as well as Suisun Bay, the Carquinez Strait and San Francisco Bay, were a river valley through which the continuation of the Sacramento and San Joaquin Rivers flowed to the Pacific Ocean. When sea levels rose again, ocean water backed up through the Carquinez Strait into the Central Valley; the combination of the narrow strait and tidal action pushing inland dramatically slowed the current of these rivers and forced them to drop sediment. The early delta was composed of shifting channels, sand dunes, alluvial fans and floodplains that underwent constant fluctuation because of rapidly rising seas – per year. About 8,000 years ago, the rate of sea-level rise slackened, allowing wetland plants to take hold in the Delta, trapping sediment; the growth and decay of these plants began to form the vast peat deposits that make up the Delta islands. The Delta reached a stabilized form similar to its mid-1800s state about 2,000–3,000 years ago. Immediately before large-scale human development, most of the Delta islands had saucer-like cross sections, with low natural levees flanking a marshy interior "bowl" that flooded intermittently with the seasons and tides. The height of these natural levees, formed from overbank deposits of sediments deposited by annual river floods, ranged from above mean high tide at Sherman Island on the Sacramento River, to at Andrus, Staten and Tyler Islands, located further east near the Mokelumne River. An estimated 60 percent of the Delta flooded for up to two hours each day at high tide; ==History==

Humans have inhabited the Delta for up to 4,300 years. The estimated indigenous population of the Delta at the time of first contact with Europeans was about 3,000–15,000, predominantly Miwok and Maidu, with some estimates ranging up to 20,000. The Native Americans lived in villages of 200–1,000 people on the eastern edge of the Delta, where the land was higher and less susceptible to flooding. Their lives centered around the abundant reeds or tules that grew on the Delta islands, which they used to make houses, boats, and garments. The Spanish conscripted large numbers of Native Americans for labor on missions; many Native Americans fled deep into the Delta in order to escape their European masters. However, this did not protect them from diseases. A malaria epidemic in 1833 decimated local native populations; this was probably exacerbated by the marshy geography of the area, which bred large amounts of mosquitoes. Because of the flat terrain coupled with year-round availability of fresh water, irrigation here was cheaper and simpler than other fertile regions of California. As a result, the Delta remained California's richest farming region (alongside Los Angeles County) until the 1940s, when massive federal water projects finally made possible the full-scale irrigation of the main body of the Central Valley. Today, the Delta is still among the state's most productive farming regions. In 1850, Congress passed the Arkansas or Swampland Act, which allowed for the transfer of title for wetlands to private owners on the conditions that the land would be reclaimed. In California, more than of wetlands were partitioned under the Swampland Act, of which were in the Sacramento–San Joaquin Delta, roughly the same amount of land that has been developed to date. Agricultural interests in the Delta were protected by the building of levees, a colossal effort first undertaken by Chinese laborers from the 1850s to the 1870s. The Board of Reclamation, formed in 1861, collectivized levee construction in the Delta by grouping islands into areas known as reclamation districts. By the 1890s, the original levee system had been largely replaced with stronger embankments consisting of clay dredged from nearby river bottoms. By 1900, about , or nearly half of the Delta's land area, had been reclaimed. Most of the farmable land in the Delta had been reclaimed by the 1920s. ==Economy and human use==

Agriculture The Delta produces crops valued at about $650 million annually (for the 1998–2004 period), making it one of the most productive farming regions of the United States in terms of crop value per unit area. Agriculture provides secondary benefits of over $2 billion to the local economy. Petroleum is shipped to both the Benicia Refinery and the Martinez Refinery by water. Nearby is the Port Chicago Marine Ocean Terminal, a facility that supports the U.S. Navy. Water supply The Delta is often considered the nexus of California's statewide water system. About half the total river flow in the state passes through this region, from which water is exported to other areas of the San Joaquin Valley, Southern California and portions of the Bay area to supply some of farmland and 23 million people in central and Southern California. The Delta provides an estimated of water per year, of which about are exported to the San Francisco Bay Area, are used locally, and over are exported to the San Joaquin Valley, coastal Central and Southern California. Today, the California Aqueduct and the Delta-Mendota Canal, two of the state's largest water conveyance facilities, both draw water from the southern end of the Delta at the Clifton Court Forebay. Built in the mid-twentieth century, the former supplies water to the Los Angeles Basin and coastal central California via the State Water Project; the latter, a part of the CVP, provides supplies of irrigation water in the fertile San Joaquin Valley. Although the vast majority of water supplied by these projects is used for agriculture and urban areas, some water is also provided for wildlife refuges and habitat conservation works. The Contra Costa Canal and North Bay Aqueduct also take Delta water, supplying the nearby San Francisco Bay Area. Locally, the Delta provides water for cities and towns in five counties and for over 1,800 agricultural users. The Delta is home to over 100 marinas and 25 yacht clubs. In 2010, over seven million 'annual visitor boating days' occurred on the Delta, according to a local government survey. Originally a Delta farming island, Franks Tract flooded in 1936 and again in 1938. The levees were never repaired and the island remained submerged, becoming an expanse of open water dotted with remnants of the original levees now the only landforms. In 1959, the area became a state park. Franks Tract State Recreation Area is accessible only by water and is used for fishing, waterfowl hunting, and boating. The Pacific Flyway, a north–south route for migratory birds, crosses the Delta. The migratory birds provide both birdwatching and hunting opportunities. Including the northern Suisun Marsh, there are over 150 private duck clubs in the area. ==Effects of the levee system and freshwater diversion==

The levee system allowed farmers to drain and reclaim almost of the Delta, then a tidal marsh. Once the rivers were confined to their riverbeds, the peat soil of the former tidal marsh was exposed to oxygen. As the oxygen-rich peat soil decomposed and then released carbon dioxide, profound subsidence of the land resulted, of up to 25 feet since the late 1800s. Currently, most of the Delta is below sea level, with a great deal of the western and central Delta at least below sea level. The California Department of Water Resources has experimented with re-flooding areas for wetland restoration, in order to sequester carbon and rebuild soil levels. Land subsidence has endangered the Delta's system of protective levees, occasionally triggering levee failure and subsequent flooding. Land subsidence also allows brackish water intrusion into the Delta, an issue compounded by the diversion of up to 25% of the freshwater flowing into the Delta. The decreased volume of freshwater in the Delta has had a profound effect on its ecology. In most years, large dams in the Delta watershed fully hold back spring runoff; as a result the Delta is most susceptible to salinity intrusion between February and June. However, regulation provided by dams helps boost freshwater flows during dry summers and autumns, reducing the risk of salinity intrusion in these months. Diversions located at the southern end of the Delta, however, have negated some of the benefits of upstream dams. The powerful pumps that supply water for the Central Valley Project and State Water Project cause water in the Delta to flow from north to south instead of the natural direction of east to west. This has caused multiple environmental issues, such as the disruption of fish migration and salinity buildup in the eastern Delta, where salts can no longer be flushed to the sea by natural river flows. ==Levee failures==

. Since 1900, there have been over 160 levee failures in the Sacramento–San Joaquin River Delta. These numbers include multiple failures of a single levee structure. Levee failures, also known as breaches, can be caused by overtopping or structural failure. One of the most recent examples of levee failure in the Sacramento–San Joaquin River Delta occurred in June 2004 when a levee breach caused more than of water to flood the entire island of Jones Tract. But, the significant improvements made to the Delta levee system since 1982 have reduced the incidence of failures to this one major failure in 30 years. The most up-to-date description and discussion of the Delta levee system can be found in the Economic Sustainability Plan of the Delta Protection Commission. This study concluded that the Delta levee system is now relatively robust but should be improved to effectively eliminate the risk of failure in extreme floods and earthquakes. It emphasizes the significant value of the infrastructure that passes through the Delta, including water conveyance, in addition to life and property, and the value of the Delta as a Place. A 2019 article states that "a catastrophic levee failure, defined as 20 islands flooding at once, has a 62 percent chance of occurring in the next two decades if subsidence isn’t addressed." Simultaneous levee failures on the Delta's 57 islands in the wake of an earthquake which allow the inflow of brackish San Francisco Bay waters could threaten the water supply for the Central Valley, which includes both the irrigation water for its $17 billion agricultural economy and the drinking water for about 25 million people. ==Ecology==

About 500 plant and animal species inhabit the Delta, which is one of the largest estuaries in western North America. Sediment deposits formed natural levees around the borders of islands, where larger trees, mainly willows, were able to take root and form large riparian forests. More extensive woodlands were prominent on the fringes of the Delta bordering the riparian zones. Composed primarily of valley oak, box elder and Oregon ash, these oak woodlands grew in bands that stretched up to inland. Farther away from water sources, vegetation gave way to grassland. The water hyacinth has become one of the most destructive plants to the Delta water way. Within one year it will spread and cover as much as of water space in one growing season. It has become a challenge to the agricultural community to eliminate. The plants spread by budding and spreading its seeds, and those seeds fall to the bottom of the water, where they can stay viable in the muck for years. The Hyacinth can form a mat up to thick, shutting off light and becoming acidic when they decompose. is an Endangered Species Act threatened species that has caused controversy over the amount of water that can be sustainably pumped from the Delta. The Delta was formerly populated by large herds of deer and tule elk; their trails were so vast that early Spanish explorers supposed the area was inhabited by cattle. Significant numbers of California grizzly bears could also be found in the Delta. A survey in 2012 recorded a spring duck population of 48.6 million, the highest since counts began in 1955. Large mammals in the Delta have not fared so well; with most of their habitat converted to agriculture, remaining populations were highly susceptible to human impacts and natural disasters. Grizzlies were hunted to extinction, while the flood of 1878 wiped out the last of the elk herds in the Delta. The survival of the Delta smelt has been one of the largest environmental issues in California, as environmental measures enacted to protect its population have often reduced the amount of water available for federal water projects that depend on water pumped from the Sacramento–San Joaquin Delta. The California Office of Environmental Health Hazard Assessment has issued a safe eating advisory for any fish caught in Central and South parts of the Delta due to elevated levels of mercury and PCBs. In addition, there is a notice of "DO NOT EAT" for any fish or shellfish from the Port of Stockton. There is a separate safe eating advisory for the Northern part of the Delta. A 2010 study shows that the anglers in the Delta who ate these fish had higher levels of mercury in their system. Delta fish have also been found to have high levels of a toxin called methylmercury which originates from old gold rush era mines in the Sierras. In that same study, it was found that women along the delta were consuming high numbers of fish, making them more susceptible to poisoning. Nutria were found in Merced County in 2017 on the edge of the Delta. State officials are concerned that they will harm the infrastructure that sends water to San Joaquin Valley farms and urban areas. The Delta has seen numerous cyanobacteria blooms with increasing frequency over the past two decades. Cyanobacteria have the potential to produce cyanotoxins which can pose a risk to humans and animals upon contact. Because of this cyanobacteria blooms are seen as a threat that has the potential to impact human life. Several types of toxic cyanobacteria have appeared in the Delta, with Microcystis aeruginosa being one of the most common types. Frequent Microcystis blooms have impacted the food web of the Delta at multiple trophic levels. Microcystis spp. blooms in the Delta were found to decrease the diversity of the aquatic microbial community. Additionally, the cyanobacteria blooms in the Delta have led to decreased zooplankton mass and density. There is also concern for further spread throughout the food web via bioaccumulation. Microcystins were detected in the tissue of clams at levels much higher than the ambient water around them because of microcystin's ability to covalently bind to tissue. The increased occurrences of cyanobacteria blooms in the Delta can be attributed to a variety of factors with the most important being lowered streamflow. Microcystis benefits greatly from anthropogenic inputs of nitrogen which allows it to out-compete other primary producers and dominate the lower trophic levels. There have also been large amounts of nutrients monitored in the Delta as a result of various human activities. The increased presence of Microcystis aeruginosa blooms in the Delta represents a continual threat for species at multiple trophic levels. The lower trophic levels are affected from both reduced diversity as well as reduced numbers through competition. Because microcystins can concentrate inside fish at multiple trophic levels it also represents a risk for human consumption as well. ==Conservation efforts==

After numerous rounds of mitigation following the 2005 Smelt Biological Opinion (BiOp) lead to pumping restrictions from the State and Federal projects from the Delta, a number of potential solutions to the Delta's problems have been proposed. These followed the CALFED process which had offered several staged solutions. A first set of alternatives would maintain the Delta in its current condition and configuration. The second would restore parts of the Delta more closely to its natural state but include the construction of an additional Peripheral Canal to maintain the water supply currently provided by the Delta. for the Floating Sensor Network project The Contra Costa County Public Works Department is working with the California Coastal Commission and the Department of Boating and Waterways to protect the drinking water quality, prevent pollution, and promote the environmental health of the Delta. Since the 1940s, various groups have lobbied for the construction of a Peripheral Canal to redirect water flowing from the Sacramento and San Joaquin rivers directly to the federal aqueducts that draw water from the southern end of the Delta. Currently, freshwater entering the Delta has to flow through a maze of river channels and sloughs before entering the Clifton Court Forebay north of Tracy, where water is pumped into the California Aqueduct and Delta-Mendota Canal. In addition, large numbers of Delta smelt and other endangered species are killed by the pumping plants that provide water for the aqueducts. The current proposal, known as the Bay Delta Conservation Plan, entails building twin tunnels under the delta and is closely associated with Governor Jerry Brown. However, the Peripheral Canal proposal has been criticized because it would further reduce the amount of freshwater flowing through the Delta. Farmers in the Delta are among the most opposed to the project because it would decrease the amount of water available to them for irrigation. All solutions, however, aim to produce a Delta which simultaneously supports a vibrant ecosystem and continues to supply fresh water to the Central Valley Project, the State Water Project and the Bay Area. The Sacramento–San Joaquin Delta National Heritage Area is managed by the Delta Protection Commission. ==See also==

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