Sacramento-San Joaquin River Delta
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The Sacramento-San Joaquin River Delta is an expansive inland river delta and estuary in northern California in the United States. It 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 (an upper arm of San Francisco Bay). The city of Stockton is located on the San Joaquin River on the eastern edge of the delta.
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[edit] Description
The Sacramento-San Joaquin River Delta is an example of an inverted river delta, one of only a few worldwide. The fan-shaped area of the delta converges downstream, rather than diverging, as the two rivers are forced to exit the Central Valley through the Coast Range via the narrow channel known as the Carquinez Strait, which leads to the San Francisco Bay and ultimately the Pacific Ocean through the Golden Gate.
The delta consists of myriad small natural and man-made channels (locally called sloughs), creating a system of isolated lowland islands and wetlands defined by dikes or levees. The delta's so-called "islands" are not really islands in the classic sense, but they are referred to as such because they are completely surrounded by water and are so isolated in many cases that they are accessible only by boat, ferry or aircraft.
An extensive system of earthen levees has allowed wide-spread farming throughout the delta. Its peat soil makes it one of the most fertile agricultural areas in California and arguably even the nation, contributing billions of dollars to the state's economy. Certain specialty crops, such as asparagus, are grown in the delta in quantities unmatched anywhere else in the United States.
The delta and its "Thousand Miles of Waterways" are a recreation destination. The warm, breezy summers are popular among water skiers and boaters and even the chilly, foggy winters draw fishermen and hunters.
[edit] Development of the Delta
The delta is an estuary which acts as the funneling point for a watershed covering thousands of square miles of California's interior. On its way to the Pacific Ocean, runoff flows through the delta from several major mountain ranges, including virtually the entire western flank of the Sierra Nevadas, the southern reaches of the Cascades, and the eastern flanks of those parts of the coast range that border the central valley. For thousands of years, huge swaths of the delta flooded regularly with every spring melt, and the delta represented one of the largest estuaries on North America's west coast.
Starting in the late 19th century, Chinese workers were used to construct hundreds of miles of levees throughout the delta's waterways in an effort to reclaim and preserve farmland and control flooding. These levees confine waterflow to the riverbeds.
Levee failures in the delta can result in the flooding of vast tracts of both agricultural land and developed cities. On June 3, 2004, a 350 foot (110 m) section of a levee 10 mi (16 km) west of Stockton collapsed, flooding the Upper Jones Tract, a 12,000 acres (49 km²) island.[1] Tens of thousands of people live near these levees (in many cases, right next to them), in scores of communities ranging from Tracy in the south to Stockton in the east, Sacramento in the north, and the San Francisco Bay Area in the west. In light of the 2005 Hurricane Katrina disaster affecting similarly low-lying river delta regions in Louisiana and Mississippi, there has been a strong outcry for the state of California and/or the federal government to thoroughly inspect and, if necessary, strengthen and repair the delta's levees.
[edit] Construction and history
The total area is around 1,100 square miles, around 70 reclaimed islands and tracts, surrounded by 1,100 miles of levees surrounded by 700 miles of waterways. The delta was originally marshland; reclamation was made by the building of levees, by Chinese laborers in the 1850s.
A typical levee was constructed as being approximately trapezoidal, 10 ft above original ground level, and approximately 30 ft wide at the base rock armoured on the river side. The construction was a colossal engineering undertaking.
 Cross section of levee construction |
 Clamshell dredge used during construction |
[edit] Major Delta Tributaries
- San Joaquin River -- including distributaries Old River and Middle River
- Sacramento River
- Mokelumne River
- Calaveras River
- Bear Creek
