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Pacific Coastal and Marine Science Center

Coastal Processes


Landsat image of San Francisco bay showing sand and mud in the water, click for full image.
Landsat image of San Francisco bay showing sand and mud in the water

San Francisco Bay is the largest estuary on the West Coast, second only to Chesapeake Bay in the United States. The combined San Francisco Bay and Sacramento-San Joaquin River Delta covers about 4,100 square kilometers (1,600 square miles). Over 40% of California drains through San Francisco Bay.

San Francisco Bay is one of the most human-altered estuaries in the world. Not surprising, since over 7 million people live in the San Francisco Bay area. In the 1800s, mining, logging, agriculture, and urbanization increased sand and mud entering San Francisco Bay. In the 1900s, dams, water projects, and river management reduced sand and mud entering San Francisco Bay. The San Francisco Bay floor, beaches, marshes, and ecosystems continue to change due to all these factors, and new ones like dredging, wetland repairs, and climate change.


Sand is a mixture of very small pieces of rocks or other materials. Sand grains are 0.0625 to 2 millimeters in size (0.00246 to 0.0787 inches).

Mud is a mixture of silt, clay, and water. Mud particles are smaller than 0.0625 millimeters (0.00246 inches).

Sediment is a mixture of sand and mud.

Aggregate (as in "aggregate mining"), is gravel and sand used for construction.

Coastal upwelling occurs when strong, consistent winds create ocean currents that bring deeper, colder water with nutrients to the surface.

Dredging is a form of mining that removes gravel, sand, and mud from underwater.

El Niño is an abnormal warming of surface waters in the eastern tropical Pacific Ocean, which affects the weather all over the world, including California. El Niño's typically last one or two years.

Erosion is the process by which sand, mud, soil, and rock are removed from the Earth's surface by wind or water.

Estuary is the mouth of a river affected by ocean tides.

Hydraulic mining uses high-pressure jets of water to blast away rocks, sand, and mud from hillsides.

Landsat is a US Government satellite system that takes color photos of the Earth.

Pacific Decadal Oscillation is like a long-lived El Niño in the north Pacific Ocean. Warm and cool phases of the PDO can last more than 10 years.

Salinity is the saltiness of water.

Storm surge is a temporary increase in sea level, caused by storms. Storm surge adds to high waves generated by storm winds.

Urbanization is the growth of cities, typically expanding into farm lands or wild lands.

Wetlands are lands saturated with water, permanently or seasonally. Distinct plants and animals live in wetlands.



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Path: coastal_processes/sfbsm/introduction.html
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Page Last Modified: 21 March 2014 (lzt)