Years before Hurricane Katrina hit, engineers knew that New Orleans was the most vulnerable spot in the country for flood damage — and some even predicted almost exactly how the tragedy would unfold.
Now the experts say California's Sacramento-San Joaquin Delta presents the next cause for concern. "The Sacramento area is perhaps, after New Orleans, the scariest spot in the country," said Nicholas Pinter, a geologist at Southern Illinois University who studies river flood risks.
The subject of future risks — and what to do about flood-prone regions ranging from Louisiana to California — was a subject of debate Saturday at the annual meeting of the American Association for the Advancement of Science. Even St. Louis, the site of this year's meeting, was considered a region at risk.
A panel of experts held out little hope that the risks would be eased, however, unless governments on all levels took a harder look at the standards for levee construction and changed policies that actually encouraged development in vulnerable areas.
It's difficult for the lessons from past floods to sink in, even when it's a flood as catastrophic as the one caused by Katrina, said the University of Maryland's Gerald Galloway, a former brigadier general in the U.S. Army Corps of Engineers.
"The half-life of the memory of a flood is very short," he told reporters. "You can already hear it in Washington D.C. ... 'New Orleans, where?'"
California delta at risk
Unlike New Orleans, the delta at the confluence of California's Sacramento and San Joaquin rivers is about 80 miles inland — and thousands of miles from the nation's hurricane zone. But like New Orleans, the delta's historic floodplains are protected by an extensive and expensive system of levees and dams. Much of Sacramento itself sits lower than the levees protecting the city.
Last fall, The Sacramento Bee reported that more than 300,000 people would be in the direct path of a flood.
The chances of a catastrophic flood occurring in the Sacramento-San Joaquin Delta sometime in the next 50 years are about two out of three, said Jeffrey Mount, director of the Center for Integrated Watershed Science and Management at the University of California at Davis.
"It is the most at-risk large metropolitan area in the country, with less than half the protection" that New Orleans had, Mount said. "It is at extreme risk due to levee failure and subsidence."
St. Louis blues
Hundreds of miles upstream from New Orleans, the increasingly corseted Mississippi River also holds the potential for catastrophic flooding, the experts said. Pinter noted that along some stretches of the river around St. Louis, flood levels are up to 12 feet (3.7 meters) higher than they were in 1900.
Pinter referred to the Great Midwest Flood of 1993, which caused an estimated $15 billion in damage. Since then, there has been $2.2 billion worth of new construction on land that was underwater in 1993, he said. New levees have been built, but in Katrina's wake, the experts said those levees may be inadequate.
In some of the historically flood-prone areas around St. Louis, "the possibility of seeing a mini-New Orleans situation here is definitely an issue," said Adolphus Busch IV, a member of St. Louis' Anheuser-Busch beer-brewing family.
Busch is working to cut back on the pace of floodplain development as chairman of the Great Rivers Habitat Alliance. The alliance has filed lawsuits in an effort to block tax incentives for development of lands that may be flooded if levees break.
Overconfident and underinsured
Saturday's panelists were unanimous in their view that current policies on flood mitigation and insurance gave too much encouragement to development — and ironically, could lead to more flood-related damage in the long run.
That doesn't mean we shouldn't build better defenses against flooding, said Norbert Schwartz of the Federal Emergency Management Agency. "Mitigation does work," he said. "For every dollar invested, you get a $5 return."
However, once a new levee is built, the requirements for federal flood insurance are eased, and developers feel more confident about going ahead with large-scale construction. "The levee-protected area gave people the impression that it is a safe area," Schwartz said.
In reality, that's usually not the case. The federal requirements call for levees to be capable of withstanding the kind of flooding that happens, on average, once a century. But Pinter said statistics indicate that the height of a "100-year flood" is being underestimated by 4 to 5 feet (1.2 to 1.5 meters).
Moreover, Pinter pointed out that although the federal government provides support for building the levees, it's up to local governments to maintain them — and many of the nation's levees are poorly maintained. Undermined levees were an Achilles' heel for New Orleans, and appear to be a weak link in California as well, he said.
Visions of the future
Looking ahead, the experts said risk assessments should consider future weather projections rather than simply assessing the historical flood record. In the short term, we're entering a La Niña weather pattern, which is associated with a greater frequency of hurricanes, Pinter said.
In the longer term, changes in global climate may lead to changes in flood risks as well, said Anthony Arquez of the National Oceanic and Atmospheric Administration. "As the climate warms, we expect more extreme precipitation events. What was once considered a 100-year flood might be a 50-year flood," he said.
One of Galloway's prescriptions would be to raise the standards for levee protection. "100 years is too low," he said. Dutch cities are built to outlast 1,250-year floods, or in some cases even 10,000-year floods, Galloway noted.
Also, Galloway said even those living behind levees in flood-prone areas should be required to carry some level of flood insurance. "There is still residual risk," he said.
Mount had a political prescription as well: "Elect a leader with some courage. The bottom line is, it's far cheaper to have floodplain management than to have flood control. ... Keep it as farms, don't turn it into houses."
Mount said the main problem — for politicians and those who live and work in the nation's floodplains as well as the wider public — is that "we live in a state of denial."
"It is pretty depressing," he acknowledged, "but it's extremely important. Just take a look at Katrina and the human suffering there."