Sacramento–San Joaquin River Delta

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Northern California's Sacramento-San Joaquin River Delta. The Sacramento River flows into the delta from the north and the San Joaquin River from the south through Stockton.
Sacramento Delta at flood stage, spring 2009. Photo by Doc Searls.

The Sacramento–San Joaquin River Delta, or California Delta, is an expansive inland river delta and estuary in Northern California in the United States. 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. The Delta is recognized for protection by the California Bays and Estuaries Policy.[1] The city of Stockton is located on the San Joaquin River on the eastern edge of the delta.

Contents

Development [edit]

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Construction and history [edit]

The total area is around 1,100 square miles (2,800 km2), around 70 reclaimed islands and tracts, surrounded by 1,100 miles (1,800 km) of levees surrounded by 700 miles (1,100 km) 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 (3.0 m) above original ground level, and approximately 30 ft (9.1 m) wide at the base rock armoured on the river side. The construction was a colossal engineering undertaking.

Effects of the levee system and freshwater diversion [edit]

Land Subsidence in the Delta 1995

The levee system allowed farmers to drain and reclaim almost a 500,000 acres (2,000 km2) 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. Now, most of the Delta is below sea level, and a great deal of the western and central Delta is at least 15 feet (4.6 m) below sea level. Land subsidence renders unstable the Delta’s 1,100-mile (1,800 km) system of protective levees, instigating levee failure and subsequent flooding. Land subsidence also allows saltwater intrusion into the Delta, compounded by water diversions that remove 40% of the freshwater flowing into the Delta. Loss of freshwater in the Delta has had a profound effect on the ecology of the Delta.[2]

Levee failure [edit]

Since 1900, there have been over 160 levee failures in the Sacramento–San Joaquin River Delta. Levee failures, also known as levee breaches, can be caused by overtopping or structural failure. Overtopping occurs when water breaches over the crest of the levee due to floods, tidal fluctuations, and/or wind-driven waves. Structural failure refers to a loss of load-carrying capacity initiated when the levee is stressed to its strength limit, thus causing a fracture or excessive deformations. Structural failure is usually caused by inadequate foundations, subsidence, seepage, erosion, and burrowing animals. Earthquakes can also cause levee failure through soil liquefaction. The most current example of levee failure in the Sacramento–San Joaquin River Delta was documented in June 2004 when a levee breach caused more than 150,000 acre·ft (190,000,000 m3) of water to flood the entire island of Jones Tract.[3]

A significant earthquake in the region (magnitude 6.5), which is not unlikely in the coming decades,[4] could cause widespread levee failure, allowing saltwater to flood the Delta and enter the canals that supply fresh water (for irrigation and drinking) to central and southern California.[5][6] This scenario is sometimes called the "Big Gulp",[4][6] and it is estimated that it would cause $40 billion of economic loss to California.[5][7] A similar result (widespread levee breaches) could also be caused by a combination of sea level rise, high tide, and storm surges.[4]

Ecology [edit]

Further, the Delta's fish population is in question. The Delta is home to approximately 22 species of fish including the Delta smelt, a key indicator species for the health of the Delta's ecosystem. In 2004, the Delta smelt was found to be on the edge of extinction.[8]

Current status [edit]

Water tower in Isleton, California

The administration of the region is also in flux. CALFED, a federal-state program in charge of the Delta, is on the verge of financial insolvency.

A number of solutions have been proposed. A first set of alternatives would maintain the Delta in its current homogeneous freshwater state. The second would return the Delta to a heterogeneous mixed salt water-fresh water body, and would serve in the Delta's current water-supply with a series of aqueducts.

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.[8]

A strong movement is emerging to construct a Peripheral Canal to redirect water flowing from the Sacramento and San Joaquin rivers directly to man-made aqueducts headed south and west. Senator Diane Feinstein and former Governor Arnold Schwarzenegger both declared their support for such a project.

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.[9]

In April 2009, the Sacramento River Delta was declared the nation's most endangered waterway system by the environmental group American Rivers, due to water shortages caused by the Delta's environmental problems, declining fish populations and aging levees, among other problems.[10]

Major tributaries [edit]

Islands [edit]

See also [edit]

Portal icon California Central Valley portal

References [edit]

  1. ^ State Water Resources Control Board Water Quality Control Policy for the Enclosed Bays and Estuaries of California (1974) State of California
  2. ^ Bay Delta Blog (Sept. 20, 2009). "Bay-Delta: Levees, Climate Change, and Water Quality". Retrieved Apr. 29, 2010. 
  3. ^ "Levee Failures in the Sacramento-San Joaquin River Delta". Department of Water Resources, State of California. Retrieved 2012-08-20. 
  4. ^ a b c KQED blog post: Three Delta Disasters that Could Disrupt California’s Water Supply
  5. ^ a b Sustainable Water and Environmental Management in the California Bay-Delta, National Academies Press 2012, [1]
  6. ^ a b World Socialist Web Site: One earthquake could leave two-thirds of Californians without drinking water, November 2005.
  7. ^ CALFED: Delta Flood Risk
  8. ^ a b "Keep the Delta Clean, Clean Boating Program (California Coastal Commission and California. Dept. of Boating and Waterways". Coastal.ca.gov. Retrieved 2012-08-20. 
  9. ^ "Dealing with the Delta: Envisioning Futures, Finding Solutions" (PDF). Retrieved 2012-08-20. 
  10. ^ [2][dead link]

External links [edit]

Coordinates: 38°04′05″N 121°50′34″W / 38.067975°N 121.8427354°W / 38.067975; -121.8427354
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