Study: Plan for bigger floods

A major new study of flood risk in California's Central Valley urges communities to use worst-case scenarios to build up their levees, rather than setting arbitrary targets based on flood probability.

Sacramento, known to have the worst flood risk of any major metropolitan area in the nation, is working to erect levees strong enough to withstand a 200-year flood, a catastrophic flood predicted to have a half-percent chance of striking in a given year.

The plans to fortify citywide levees by 2015 have ignited a levee war between local and federal officials because they call for restrictions that could result in a building moratorium in the city's fast-growing Natomas basin.

But instead of setting 200-year safety goals, the new study suggests even stronger flood-protection measures – guidelines that may invite even more controversy in the future.

Citing the Valley's "severe" flood risk, the report by a national panel of experts urges California to go further than the legislative steps taken last year to control floodplain development and improve levees.

One of those new laws pushes communities toward that 200-year flood protection, or about double what exists today in most of the Sacramento region.

The report released Thursday instead urges California communities to prepare for the "standard project flood," which defines a worst-case storm using historical weather records, storm behavior and runoff intensity.

This would result in protection that exceeds the 200-year threshold and may reach 500-year protection, said the panel's chairman, Gerald Galloway, a former brigadier general at the U.S. Army Corps of Engineers.

"It will require higher levees," said Galloway, now a professor of engineering at the University of Maryland. "This is going to require a substantial investment in structural protection, and it's going to require wise use of the floodplain."

The study was commissioned in July by California's Department of Water Resources. The 13-member panel included engineering and environmental experts from the University of California and throughout the nation.

The study's authors praise California for strides it has taken to rein in flood risk, considered to be among the worst in the nation due to storm intensity, rapid urbanization and deteriorating levees.

The Legislature and Gov. Arnold Schwarzenegger last year approved six bills to move the state toward 200-year flood protection and to control risky floodplain development. In 2006, voters approved two bond measures that will raise $5 billion for flood-control projects.

"California is setting the tone for the rest of the nation in how to deal with the problem," said Galloway. "Our report says that's a giant step forward, but you need more steps. You haven't solved the problem."

DWR Director Lester Snow said he is pleased the report affirms the state's recent efforts. And, he said, the state is prepared to plan for greater protection risk suggested by the authors.

"They also recognize we need to engage the business community, developers and local governments to continue moving forward," he said. "We will do that."

One new state law forbids local government from approving new housing in floodplains after 2015, unless the area has – or is planning – 200-year flood protection. Another holds local government liable for damages if it "unreasonably" approves floodplain development, a standard criticized as vague.

The study team said that's not good enough.

Instead, they said, all the Valley's flood-threatened urban areas should have at least 200-year flood protection by 2020, regardless of development pressure.

The team recommended convening a scientific panel to decide how much protection each community needs. The outcome would be based on the so-called "standard project flood."

The report also recommends that future development should not occur in floodplains, and that existing rural lands in floodplains should be off-limits to development.

Local governments also must have proper land-use controls to enforce these requirements, and must share financial liability for any flood damages that do occur.

And, where feasible, new levees should be set back from the river to create more wildlife habitat and a wider river channel to reduce flood levels. Most levees were intentionally built close together to create narrow river channels to scour away sediment left by hydraulic gold mining, a strategy no longer needed.

The study recommends that anyone living behind even the strongest of levees should be required to purchase flood insurance. And long-term funding and oversight must exist to ensure levees are maintained in top condition.

Taken together, the recommendations would require a huge investment by state and local governments – several times more than the $5 billion already approved by voters.

"The tough decision is figuring out how to get people together to work on these issues," Galloway said. "You've got your hands full because there's such tremendous pressure for growth."

Yolo County Supervisor Mike McGowan, board member of the Delta Protection Commission, supported most of the report's conclusions. But he objects to a blanket ban on floodplain development and the notion that local communities should share liability for flood damages.

"I agree that the thoughtless proliferation of urbanized growth in floodplains is wrongheaded," he said. "But it doesn't mean that you can just say 'no' completely to everything, because we are a society and an economy that's based on growth and expansion."

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