"Experts in coastal geology, storm surge behavior, levee engineering, and other disciplines who focus on the unique coastal region of Louisiana point to the critical work that mud, sand, and river sediment must play in creating a city that would be able to withstand another devastating natural disaster."In other words, the levees that have protected the city from flooding have also contributed to the city sinking below sea level. After raising most of the city above sea level, the levees must also be raised to levels that can withstand a Category 5 hurricane--but even that is not enough:
Mr. Suhayda envisions a rebuilding plan that begins with levees that are higher than the 14-foot levee needed for a category 3 storm. On Wednesday, he said he stood in the gap of one of the broken levees.Plan C, according to Suhayda, is for essential buildings like hospitals--which were never part of the evacuation plan--to get their generators out of the basement and above the possible flood.
“The water that came through this spot flooded 80 percent of the city,” he said. “Let’s build a category 5 levee, but let’s assume it will fail,” said Mr. Suhayda. “We have to have back-up plans B and C.”
Plan B, in Mr. Suhayda’s view, would prevent the near total inundation of the city by a single levee breach, as happened in Katrina.
“We have to compartmentalize the city like waterproof chambers in an ocean liner,’’ he said.
“A majority of the levees performed exactly as they should,’’ he said, but that didn’t save the city. Compartmentalizing would allow the good levees to do their protective job.
A step that should be taken in conjunction with this is restoring wetland areas south and east of New Orleans, which would act as a buffer for New Orleans:
While improved levees seem a nearly inarguable condition for a rebuilt New Orleans, others see protection against future storm surges as a far more practical solution than raising a sinking landscape by filling in the lowlands.
“Geologically, it makes more sense to me to think about protection of New Orleans, rather than try to fill New Orleans with sediment,’’ said Mr. Roberts.
It’s a matter of restoring lost friction. Hurricanes slow when they cross land, and for centuries Louisiana’s 7,000 square miles of coastal wetlands acted as a natural brake on raging storms. But the processes that built the marshlands over 5,000 years are gone, victims of human settlement. The river no longer floods, and it was flooding that released sediment into the ever-renewing delta wetlands. Much of the sediment that would have maintained the wetlands now jets into the Gulf of Mexico.
Activities like oil and gas exploration and canal dredging compounded the sediment loss. So does the natural subsidence of the watery marshlands in an era of rising sea levels.
As a result, Louisiana lost 1,900 square miles of wetlands from 1930 to 2000. If nothing changes, another 700 square miles will disappear in the next 50 years, according to a U.S. Geological Survey report issued in 2003.
The problem, of course, is that all of this will cost hundreds of billions of dollars--and the political will to follow this course over the next ten to twenty years. Expecting this kind of leadership from the present Republican leadership, however, is about as intelligent as spitting into Katrina-force winds.