The plan, adopted by the Central Valley Flood Protection Board, calls for as much as $17 billion in repairs and new investments in the levees and other infrastructure, including $5 billion in bond funds already approved by state voters.
Officials and experts agree the flood control system built along the Sacramento and San Joaquin rivers by farmers and governments over the past 150 years is in disrepair.
In addition, the Central Valley region where the two rivers meet, once a mostly agricultural, lightly populated area, has experienced rapid development and population growth.
About a million Californians live in the floodplains, and the levees protect an estimated $69 billion in assets, including the state's water supply, major freeways, agricultural land and the valley's remaining wetland and riparian habitat.
Yet more than half of the region's urban and rural levees do not meet standards. And about half of the channels are believed to be inadequate to handle projected flooding.
In 2006, after Hurricane Katrina on the Gulf Coast, former Gov. Arnold Schwarzenegger declared a state of emergency for California's levee system and ordered critical repairs. That same year, voters approved nearly $5 billion in bond funds for flood protection projects statewide.
Legislators also mandated that the state develop a plan to reduce flood risks. Officials said money for actual projects to be done under the plan approved Friday would come from a mixture of federal, state and local sources, with investments would be spread over the next 20 to 25 years.
The plan adopted Friday doesn't include specific projects but offers recommendations concerning floodway and bypass expansion; improvements to intake and gate structures; urban and rural levee repairs; fish passage improvements; and ecosystem restoration.
It also calls for limiting growth in undeveloped floodplains and encourages smarter land use planning. It advocates purchasing conservation easements to prevent urban development.
The plan also outlines new flood protection requirements for cities and counties. The state will now require urban communities that want to do new development to achieve 200-year flood protection -- double the federal standard -- by 2025.
While the plan recommends bypass expansions in the next five years -- an idea strongly opposed by farmers, whose land would be flooded -- it specifies that modifications should focus first on the furthest downstream bypasses in the systems, such as the Yolo and the proposed Paradise Cut bypasses.
The plan eliminates the hotly contested Feather River bypass and effectively nixes the U.S. Army Corps of Engineers' strategy for vegetation management on levees, instead allowing some vegetation on or near the structures.
Finally, it instructs the state to conduct additional analyses on the effects of climate change and the effectiveness of improvements meant to accommodate future changes in hydrology and sea level rise.
