DWR Levee Repairs Program
3464 El Camino Avenue,
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Approximately 150 years ago, the levees of the Sacramento-San Joaquin Delta were raised to prevent flooding on what remains some of the most fertile farmland in the nation. While the peat soils were excellent for agriculture, they were not the best choice to create strong foundations for levee barriers meant to contain a constant flow of river water. Nevertheless, it was these native soils that were primarily used to create the levee system.
As farmers settled the valleys, the Gold Rush drew prospectors to the hills. As mining in the Sierra Nevada turned to the more "efficient" methods of hydraulic mining, the use of environmentally destructive high-pressure water jets washed entire mountainsides into local streams and rivers. As a result, the enormous amounts of silt deposited in the riverbeds of the Central Valley increased flood risk. As a remedy to these rising riverbeds, levees were built very close to the river channels to keep water velocity high and thereby scour away the sediment.
However, the design of these narrow channels has been too successful. While the Gold Rush silt is long gone, the erosive force of the constrained river continues to eat away at the levee system. In addition, the peat soils of the Delta have subsided, gradually lowering the elevations of Delta islands (see graphic, below). As a result, some of these parcels are now more than 20 feet below sea level.
Many other changes have also taken place in the Delta over the past 150 years. Today, the levees protect not only farms but also hundreds of thousands of people who live and work in Central Valley communities.
State highways, railroad lines, water supply pipelines that serve much of the San Francisco Bay area, energy transmission lines, and petroleum pipelines also now cross the Delta and rely on the continued stability of Delta levees.
Altogether, more than $47 billion in infrastructure is protected by Central Valley levees.
(For more information on Levee Construction, Flood History, and Flood Protection Levels, please click the links at upper right.)