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Focusing on Our Delta: Diked, Dredged, and Diverted - April 3, Berkeley

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The Sacramento-San Joaquin River Delta is an expansive inland river delta and estuary, formed by the convergence of five major rivers, including the Sacramento and San Joaquin rivers (see map). Water from the western side of the Sierra Nevadas, the southern reaches of the Cascades, and the coast range are funneled through this river system forming a watershed that covers thousands of square miles. The delta is unusual in its shape in that the fan converges (rather than diverges) as the waters exit the Central Valley via the narrow channel of the Carquinez Strait and then empty into the San Francisco Bay, through the Golden Gate and ultimately the Pacific Ocean.

For thousands of years, huge areas of the Delta flooded with each spring melt. However, starting in the late 19th century, hundreds of miles of levees were constructed by Chinese workers in an effort to control flooding and to preserve the land for farming. These laborers were replaced by steam-powered dredges in the late 1870s, and by the 1920s nearly all the marshland had been reclaimed and many waterways were expanded for navigation.

The Delta today:

  • Covers 738,000 acres and consists of hundreds of miles of waterways
  • Is home to more than half a million people
  • Sustains one of the most fertile agricultural areas in the nation
  • Contributes billions of dollars to the state’s economy.
  • Is a popular recreation destination

As a natural system:

  • The Delta provides essential habitats for 230 species of birds, 150 species of flowering plants, 52 species of fish, and 45 species of mammals. Some of these species live only in the Delta region and no where else.
  • Routine fish surveys conducted in the fall of 2004 found that native fish populations are in drastic decline and some are under threat of extinction.
  • The Delta smelt is an open-water (pelagic) species that is endangered and listed under federeal and state Endangered Species Acts. This fish is sometimes seen as an indicator of ecosystem health – if the delta smelt population sharply declines, the ecosystem health is compromised.
  • The Delta consists of both salt and fresh water flows, a mixture that varies with location in the Delta relative to incoming fresh water from the mountains and salt water from the ocean.

Californians rely on the Delta as a primary source of our drinking water and our major highways, railways, gas and electricity lines cross over and through the region. But as important as the Delta is, it is also at extraordinary risk. Much of the land in the region has subsided and now rests below sea level. It is protected only by a complex and aging system of levees threatened by earthquakes, river floods, climate and sea level change. Following the disaster that struck New Orleans, there is a renewed focus on how to strengthen the levee system and to protect the Delta region that is so vital to the entire state.



Delta - a fan-shaped area at the lower end or mouth of a river, formed by eroded material that has been carried downstream and deposited

Estuary - A semi-enclosed body of water with one or more rivers flowing into it and what connects to the open sea. The water is brackish as seawater is diluted by fresh water and there is usually a high rate of biological productivity.


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