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Delta Islands & Levees Feasibility Study

This feasibility study is the Corps’ mechanism to participate in a cost-shared solution to a variety of water resources needs for which we have the authority. Results of the Department of Water Resources' (DWR) Delta Risk Management Strategy (DRMS) studies will be used to define problems, opportunities, and specific planning objectives.

The feasibility study will address flood risk management challenges and ecosystem restoration opportunities. A feasibility cost-sharing agreement (FCSA) was executed May 26, 2006 with DWR, our non-Federal sponsor.

Overview: The Corps in the Delta

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The Sacramento-San Joaquin River Delta, also known as the California Bay Delta, is the West Coast’s largest estuary; a critically-threatened and nationally-significant ecosystem and the heart of California’s water supply system that serves as many as 25 million people.

The Delta is a web of channels and reclaimed islands at the confluence of the Sacramento, San Joaquin, Cosumnes, Mokelumne and Calaveras rivers, and the outlet for Central Valley rivers to the San Francisco Bay. Much of the land is below sea level and is outlined by a network of 1,100 miles of levees constructed during the past 150 years to manage the flow of water through the Delta. The network is a mix of federal and non-federal levees and most do not meet Corps levee construction standards and could fail at water levels well below the top of the structures.

Historically, the Delta was defined by tidal wetlands, primarily comprised of peat soils. The Swamp and Overflow Land Act of 1850 transferred ownership of all swamp and overflow land, including Delta marshes, from the federal government to private parties. This Act triggered the reclamation of wetlands in the Delta through the construction of levees and drainage channels, typically by the new land owners. The majority of levees in the Delta are still privately owned and maintained. Nearly three fourths of the Delta is now in agriculture. Nearly 95 percent of the historic wetland habitat in the Delta has been converted to agricultural and urban uses.

Native habitat and natural river function in the Delta have been degraded by construction of the levee network and conversion of the floodplain to agricultural and rural development, as well as management of the system for municipal, industrial and agricultural water supplies.

The Delta was named an ecosystem of national significance. It is a critical link in the Pacific Flyway, a major north-south route of travel for migratory birds in America, and is protected through the Migratory Bird Treaty Act of 1918.

Natural resource specialists agree that the remaining ecosystems in the Delta no longer maintain the functions and richness that defined the pre-channelized system, and that the measures of ecological health will continue to decline without preventive action. Not only is it certain that these natural systems will not recover their defining attributes under current conditions, it is unlikely that even the current, degraded ecological conditions can be sustained into the future.

 

Concern elevated during the 1990s that widespread failure of Delta levees – especially after an earthquake – could cause salt water from San Francisco Bay to intrude into the Delta, effectively shutting down water supply for the 25 million Californians who depend on water pumped from the Delta. This concern resulted in two broad Corps initiatives.

First, to address the immediate threat of levee failure, Congress authorized the CALFED Levee Stability Program, which provided funding for a suite of individual levee fixes to quickly shore up weak spots. While that program produced 31 reconnaissance-level reports for individual projects, and funded the completion of the Delta Flood Map Book, it has not resulted in any projects moving toward construction. Its remaining appropriated funded is being used to further improve Corps and state Delta flood emergency response coordination under a memorandum of agreement with DWR.

Second, the Delta Islands and Levees Feasibility Study (Delta Study), is the Corps’ mechanism to participate in a cost-shared solution to address ecosystem restoration and flood risk management in the Delta and Suisun Marsh area. A feasibility cost-share agreement was executed in May 2006 with the California Department of Water Resources, the non-Federal sponsor for the study.

 

In February 2014 the tentatively selected National Environmental Restoration plan was chosen as the most reasonably efficient contribution to the California Delta, proposing to restore 83.8 acres of intertidal marsh habitat at Big Break at a cost of approximately $30 million. This plan provides a unique opportunity to restore intertidal marsh, habitat which is now greatly reduced in this ecosystem of national significance.

This tentatively selected plan links the proposed ecosystem restoration actions to ongoing Corps navigation projects, providing a cost-effective mechanism to implement otherwise costly subsidence reversal, resulting in restoration of habitat for multiple federally-listed species, notably salmonids and Delta smelt. The restored habitat would also benefit the millions of migratory fowl on the Pacific Flyway as they travel through the Delta.

Flood Emergency Response Map Book

image - page from flood emergency response map book

Produced with the California Department of Water Resources in 2011, this map book provides a working framework to aid each Delta community in their emergency response planning.

A full PDF version may be downloaded HERE. (File size 180MB)

A KMZ version of the content (compatible with Google Earth) may be downloaded HERE.

Current Status -- Delta Study

  Chief's Report - December 2018

  Final NEPA Review - September 2018

  Agency Decision Milestone - May 24, 2017

  Public Meetings (Draft Report) - May 2014

  Tentatively Selected Plan Milestone - Feb 2014

  Alternatives Milestone - April 2013

  Public Scoping Meetings - February 2013

  Re-Scoping Charettes - August & December 2012

  Federal Cost Share Agreement signed -- May 2006

Contact Information -- Delta Study

If you are interested in sharing information relevant to this project, please contact us:

Phone: 916-557-5100

E-mail: deltastudy@usace.army.mil

Mailing Address:
U.S. Army Corps of Engineers
Sacramento District
Attn: Delta Study
1325 J Street, Room 1513
Sacramento, CA  95814