Down in bayou country, the Mississippi River's spreading fingers have spent the past 7,000 years building, then deserting, old riverbanks as they course through the delta toward the Gulf of Mexico. Topped with crushed clamshells, many of these old banks have become virtually the only roads through the region.
When New Orleans native Donald Boesch was younger, he'd drive along some of these roads, pull over, and see marsh grass stretching to the horizon. "There would be little lakes in there," he recalls. "But from that vantage point, it looked for all the world like it was a huge sea of grass."
Today, many of those same spots look like vast lakes, dotted by the odd stand of grass, adds Dr. Boesch, president of the University of Maryland's Center for Environmental Science.
As federal, state, and local officials begin planning for New Orleans's recovery, many specialists say they expect the disaster to jump-start efforts to rebuild these wetlands and the barrier islands just offshore. These natural features represent New Orleans's first line of defense against the storm surges that accompany hurricanes. But over the past half century, levees and canals, which were designed to reduce flood damage and support oil and gas pipelines and facilities, have substantially weakened these defenses.
Meanwhile, funding for comprehensive plans to rebuild the wetlands has run at a trickle. In 1998, state and federal agencies offered up a $14 billion, 30-year restoration blueprint. The first $2 billion appears in a water-resources bill now working its way through Congress. The measure would authorize three major water-diversion projects and a barrier-island restoration effort.
This is a critical starting point, analysts say. But Katrina has raised the overall effort to that of "a national emergency," as one specialist puts it.
Held up against the bill for Katrina's damage, estimated to reach at least $26 billion, and with Congress focused on a $10.5 billion recovery package, wetlands and barrier-island restoration increasingly looks like a cost-effective insurance package.
"There are a number of barrier island and water diversions projects that are clearly ready to be built today," says Scott Faber, a water-resources expert with Environmental Defense in Washington.
"Unfortunately, we've not treated this issue with as great a sense of urgency as we probably should have in the wake of what's happened" since Katrina made its Gulf Coast landfall last week, he adds. "The time frames that we've imaged for completing coastal restoration, which have been decades, must now be shortened to years."
Rebuilding won't be easy.
"This is one of the most industrialized, highly engineered delta systems in the world," says Robert Twilley, director of the Wetlands Biogeochemistry Institute at Louisiana State University (LSU) in Baton Rouge.
If successful, the techniques applied to Louisiana could be used on river deltas around the world where population growth and industrial development are undermining the natural processes that serve as bulwarks against storm damage, he adds.
For New Orleans, however, the effort is critical to the city's long-term survival.
"New Orleans will not be safe from another disaster like hurricane Katrina unless we begin to restore this natural hurricane buffer," Mr. Faber says.
Since 1930, the delta has shrunk by 1,900 square miles, researchers say, an area 25 percent larger than Rhode Island. The delta stands to lose another 470 square miles by 2050 if nothing is done. Every half hour, a football-field-size patch of delta vanishes underwater.
River deltas represent a delicate balance between natural subsidence, storm erosion, and replenishment. The Mississippi delta has been sinking for millenia. Fresh delta sediments pile on top of existing deposits, squeezing water from lower layers and causing them to settle. The entire geological sandwich weighs down on the crust below, causing it to sag. But until the 1930s, silt carried down the Mississippi rebuilt the delta faster than it sank, Boesch explains.
Following a disastrous Mississippi flood in 1927, the federal government began building levees in earnest to protect New Orleans. Oil and gas development in the region added to the problem as exploration companies built canals across the delta for building drilling platforms and for routing pipelines. Shipping canals for better access to the Port of New Orleans further disrupted the delta's natural processes. Silt that once replenished the delta, nourishing its oceans of marsh grass, flowed straight into the Gulf of Mexico.
The effect of this loss on storm surges is marked. In 1993, a team from LSU calculated that oil and gas facilities in key locations on the delta were far more vulnerable to a storm surge in 1990 than they would have been in 1940. Over that period, wetlands in the study region, which included key oil and gas facilities, shrank by 24 percent, bringing the coastline ever closer. After combining the height of the storm surge in a Category 3 hurricane with the height of the waves riding atop the surge, the team calculated that this one-two punch would be 10 to 12 feet higher at key sites in the study region in 1990 than in 1940.
The team looked "25 to 30 years into the future, and indeed with the continued demise of the coast, the inundation continued to increase," says Gregory Stone, a professor at LSU's Coastal Studies Institute who led the research team.
For more than 10 years, the federal government has funded pilot restoration projects at about $50 million a year. The projects have been spread out over some 2.5 million acres and "have shown some early evidence of being very effective," says LSU's Professor Twilley.
One of the challenges is finding the silt and sand to use to restore the delta and its barrier islands.
While the Mississippi still draws silt from America's heartland, the river carries 67 percent less sediment that it did 50 years ago, "cleansed" by dams and flood-control projects upriver. One of the most immediate priorities is to conduct an inventory of natural materials available.
In the end, restoration will rely heavily on engineering - building water-diversion projects to bring the periodic floods back to key portions of the delta, as well as dredging to supply materials to fill in the vast gaps.
It also may require closing a key canal that long has had support of the shipping industry - and for this storm, may have been a weak link in New Orleans' hurricane armor.
The storm surge that caused Lake Pontchartrain to break through to the city appears to have traveled right up the canal, the University of Maryland's Boesch says.