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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.
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
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