Sacramento–San Joaquin River Delta
The Sacramento–San Joaquin River Delta, or California Delta, is an expansive inland river delta and estuary in Central California and Northern California. The delta is formed at the western edge of the Central Valley by the confluence of the Sacramento and San Joaquin rivers and lies just east of where the rivers enter Suisun Bay, which flows into San Francisco Bay, then the Pacific Ocean via San Pablo Bay. The Delta is recognized for protection by the California Bays and Estuaries Policy. Sacramento–San Joaquin Delta was designated a National Heritage Area on March 12, 2019. The city of Stockton is located on the San Joaquin River at the eastern edge of the delta. The total area of the Delta, including both land and water, is about. Its population is around 500,000.
The Delta was formed by rising sea level following glaciation, leading to the accumulation of Sacramento and San Joaquin River sediments behind the Carquinez Strait, the sole outlet from the Central Valley to San Pablo Bay. The narrowness of the Carquinez Strait coupled with tidal action has caused the sediment to pile up, forming expansive islands. Geologically, the Delta has existed for about 10,000 years, since the end of the Last Glacial Period. In its natural state, the Delta was a large freshwater marsh, consisting of many shallow channels and sloughs surrounding low islands of peat and tule.
Since the mid-19th century, most of the region has been gradually claimed for agriculture. Wind erosion and oxidation have led to widespread subsidence on the Central Delta islands; much of the Delta region today sits below sea level, behind levees earning it the nickname "California's Holland". Much of the water supply for Central California and Southern California is also derived from the Delta, via pumps located at the southern end of the Delta. The pumps deliver water for irrigation in the San Joaquin Valley and municipal water supply for Southern California.
Geography
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.Altogether, the Delta covers, with, or nearly 73 percent, devoted to agriculture. About of the Delta area is urban and are undeveloped land. The rivers, streams, sloughs and waterways of the Delta total about of surface, although this fluctuates greatly with seasons and tides. Geologically, it is not considered a true river delta, but rather an inverted river delta, as it formed inward rather than outward. The only other major river delta in the world located this far inland is the Pearl River Delta in China.
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 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.
Image:SacDelta1.jpg|thumb|right|450px|An 1850 drawing of the Sacramento River in the Delta, showing the lush foliage that made up much of the virgin Delta.
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; during spring tides or river floods, it was not uncommon for the entire Delta to be under water.
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. Staple foods included tule roots and pollen, acorns, wild fruits and seeds, fish and game.Europeans first entered the Delta region in 1772, when Spanish explorer Don Pedro Fages and missionary Juan Crespí observed the Delta from the summit of nearby Mount Diablo. For decades, the Delta was little utilized by the Spanish colonists. Expeditions from 1806 to 1812 failed to locate suitable mission sites in the Delta area. However, frequent military expeditions were made into the Delta from 1813 to 1845 in response to animosities between the Native Americans and the Spanish and later Mexicans; also several land grants were made in the vicinity of the Delta, including one to John Augustus Sutter, who started the first significant European settlement in the Central Valley just north of the Delta near present-day Sacramento.
Image:Map of the San Joaquin, Sacramento and Tulare Valleys 1873.jpg|thumb|right|An 1873 map showing the river systems of the Central Valley, with wetlands marked in gray. The Delta, at roughly left center, was the largest area of contiguous, perennial wetlands in pre-development California.
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.
The agricultural value of the Delta was first recognized during the California Gold Rush, when farmers planted orchards on Delta islands to provide fresh fruit for mining camps in the Sierra Nevada. 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 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. The early levees were built of peat, and were highly susceptible to wind and water erosion. The Great Flood of 1862 obliterated much of the existing Delta infrastructure, forcing landowners to rebuild their levees higher and stronger; more flooding in 1878 and 1881 reinforced these notions.
Although land holdings in the Delta were initially limited to per buyer, this limit was repealed in 1868, allowing large agricultural conglomerates to take entire islands and carry out massive reclamation projects. From 1868 to 1869, the entirety of Sherman Island, some, was diked and drained by a system of levees, flumes and floodgates. 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.