Gregory Gunter of the U.S. Army Corps of Engineers trumpets the new systems as a defense against the so-called “100-year storm”—a tempest so bad it has only a 1 percent chance of striking in a given year.
The system shouldn’t fail in a “400-year” Katrina-strength storm either, although Gunter says such a surge would probably flow over the barriers. This would lead to some flooding, but nothing like the scale of Katrina, which pushed over walls and breached levees. [New Scientist]
However, flood experts point out, the people who really know about keeping flood waters at bay—the Dutch—build their levees with a much larger investment, intending them to withstand a “10,000-year” event. In addition, because our hurricane records go back only so far, and because the past may not be an accurate picture of future storms, those year designations may be misleading anyway.
Paul Kemp, director of the National Audubon Society’s Louisiana Coastal Initiative in Baton Rouge, and former storm surge modeller, says the new designs presume that future storms will resemble past ones. He points out that climate change may increase hurricane strength. [New Scientist]
Don’t Forget the Wetlands
The Corps of Engineers has taken its share about abuse for Katrina failures (including by New Orleans resident Harry Shearer of The Simpsons and This Is Spinal Tap fame, whose new Katrina documentary is out now). The levees weren’t the only problem, though: New Orleans’ degraded wetlands put the city in added danger.
According to the Army Corps, all of the levees that failed during Katrina lacked wetland protection; the levees with a wetland buffer remained intact. Scientists have estimated that storm surge is diminished by one foot for every square-mile of wetland it travels through [National Geographic].
Now, groups like the Sierra Club are trying to revive the cypress ecosystem that once thrived in the shallow waters, and are doing so with a plan that actually requires pumping in partially treated sewage. With a high enough volume of biosolids—semi-treated sewage—they could add up to four feet of new material in which plants could take root.