page_title: Sacramento–San Joaquin River Delta
section_title: Levee failures
hierarchical_section_title: Sacramento–San Joaquin River Delta / Levee failures
caption_attribution_description: Sacramento–San Joaquin River Delta at flood stage, 2009. King Edward Island is inundated with water on the right. Bradford Island is on the left, and Bethel Island is below, in California's Delta region.
context_page_description: The Sacramento–San Joaquin River Delta, or California Delta, is an expansive inland river delta and estuary in Northern California. 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. Sacramento–San Joaquin Delta was designated a National Heritage Area on March 12, 2019. The city of Stockton is located on the San Joaquin River on the eastern edge of the delta. The total area of the Delta, including both land and water, is about 1,100 square miles. Its population is around 500,000 residents.
  The Delta was formed by the raising of sea level following glaciation, leading to the accumulation of Sacramento and San Joaquin River sediments behind the Carquinez Strait, the sole outlet from the Central Valley to the San Pablo and San Francisco Bays and the Pacific Ocean. The narrowness of the Carquinez Strait coupled with tidal action has caused the sediment to pile up, forming expansive islands.
context_section_description: Since 1900, there have been over 160 levee failures in the Sacramento–San Joaquin River Delta. These numbers include multiple failures of a single levee structure. Levee failures, also known as breaches, can be caused by overtopping or structural failure.  One of the most recent examples of levee failure in the Sacramento–San Joaquin River Delta occurred in June 2004 when a levee breach caused more than 150,000 acre feet (190,000,000 m³) of water to flood the entire island of Jones Tract.
  But, the significant improvements made to the Delta levee system since 1982 have reduced the incidence of failures to this one major failure in 30 years.  The most up-to-date description and discussion of the Delta levee system can be found in the Economic Sustainability Plan of the Delta Protection Commission. This study concluded that the Delta levee system is now relatively robust but should be improved to effectively eliminate the risk of failure in extreme floods and earthquakes. It emphasizes the significant value of the infrastructure that passes through the Delta, including water conveyance, in addition to life and property, and the value of the Delta as a Place.
  A 2019 article states that "a catastrophic levee failure, defined as 20 islands flooding at once, has a 62 percent chance of occurring in the next two decades if subsidence isn’t addressed."  
  Simultaneous levee failures on the Delta's 57 islands in the wake of an earthquake which allow the inflow of brackish San Francisco Bay waters could threaten the water supply for the Central Valley, which includes both the irrigation water for its $17 billion agricultural economy and the drinking water for about 25 million people.
caption: Sacramento-San Joaquin Delta at flood stage, spring 2009. Photo by Doc Searls.
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