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Last modified
7/14/2011 11:14:48 AM
Creation date
9/30/2006 10:21:51 PM
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Publications
Year
1998
Title
Layperson's Guide to Flood Management
CWCB Section
Watershed & Flood Protection
Author
California Water Education Foundation
Description
Layperson's Guide to Flood Management
Publications - Doc Type
Other
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<br />Levees <br /> <br />. <br /> <br />A major flood control feature throughout California <br />and the West is the thousands ot miles of levees <br />built over the past 100 years to help contain the larger <br />streams and rivers. Levees within California's <br />enormous system were built by local entities, the <br />state and the Corps, Over the years, some private <br />levees have been improved by the Corps and <br />incorporated into federal flood control projects, <br /> <br />Within the Central Valley, responsibility for levee <br />maintenance is spread through three governmental <br />levels, After the Corps completes a congressionally <br />authorized levee construction project, maintenance <br />responsibility is turned over to the state Reclamation <br />Board which passes this responsibility on to a <br />local agency, Within the Central Valley, the <br /> <br />mmD'ZII <br /> <br />Nowhere in California is the levee system more <br />extensive or more tenuous than in the Sacramento- <br />San Joaquin Delta, The Delta, which lies southwest <br />of Sacramento and drains westward into the <br />San Francisco Bay, is <br />an integral part of a <br />natural conveyance <br />system that has been <br />extensively modified <br />to deliver part of the <br />water supplies that <br />quenches the thirst of <br />two-thirds of the <br />state's population <br />and irrigates millions <br />of acres of tarm land, <br /> <br /> <br />Federal and state crea's <br />replI;r and strengthen <br />Delta levees broken <br />{[lid Iveakened by .\'urxing <br />f700d waters. <br /> <br />14 <br /> <br />Levee maintenance <br />is crucial to the water <br />supply, A levee break <br />near Isleton in June <br />1972 allowed large <br />volumes of brackish <br />water from San Fran- <br />cisco Bay to rush into <br />the Delta, curtailing <br />State Water Project- <br />the state's major distribution system for urban water <br />supplies - CVP and Contra Costa Water District <br />export operations, Approximately 300,000 acre- <br />feet of fresh water was released from upstream <br />reservoirs to help flush the intruding salt water out <br />of the Delta, If another Delta levee break occurs, a <br />smaller quantity of water from New Melones Dam <br />along the Stanislaus River, constructed in the iate <br /> <br />Reclamation Board oversees inspections and <br />controls encroachments through its regulatory <br />authority over federal levees, Development of <br />the levee system has impacted the riparian <br />environment. <br /> <br /> <br />Stream banks are often covered with layer of rocks <br />in a process known as riprapping to protect it from <br />eroding back to the levee and causing levee failure. <br />Maintaining agencies were required to keep the <br />vegetation cleared of vegetation to prevent <br />decreased channel flow and to ease inspections. <br />With the concern over the loss of riparian habitat <br />and the wildlife it sustains, flood management <br />officials began allowing vegetation to grow on <br />rip-rap in selected locations. <br /> <br />1970s, could be used to push salt water back <br />more efficiently, according to DWR. <br /> <br />Levee managers are not only plagued by levee <br />breaks but also by the subsidence of the levees and <br />Delta islands, Many of the central and western Delta <br />islands contain rich organic peat soil that is being <br />lost, lowering the island floors by as much as 2 inches <br />to 3 inches per year and weakening the levees. <br /> <br />Damage done by the 1986 flood prompted the <br />California Legislature to fund the rebuilding and <br />strengthening of numerous non-federal levees, many <br />of which were in serious need of repair. In 1988, the <br />Legislature passed the Delta Levee Flood Protec. <br />tion Act (SB 34), allocating $120 million over a <br />1 O.year period, The money was divided between a <br />stepped.up subventions program (a state cost- <br />sharing program) and special flood control projects, <br />Under fhe subventions program, upon approval by <br />the Reclamation Board, local agencies are compen- <br />sated up to 75 percent for levee maintenance costs <br />and improvements. <br /> <br />The S8 34 funded levee improvement measures <br />were credited with mitigating damage to Delta levees <br />during the January 1997 floods, There were consid. <br />erable concerns about the massive flows surging into <br />the Delta from the Sacramento and San Joaquin river <br />systems that pounded the levees. Anxiety increased <br />as the highest tides of the year from the San <br />Francisco Bay washed in at the height of the flood, <br />ing, which raised the water level and slowed the <br />outllow of the flood waters, further stressing the <br />levees, But overall, the levees held, <br />
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