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AFTER KATRINA:Erik Stokstad
| Small steps.
Restoration happens at many scales, such as planting vegetation.
Broader action is critically needed, scientists say.
CREDIT: ERIK ZOBRIST/NOAA RESTORATION CENTER
Robbed of sediments
Coastal degradation was a problem long before Katrina roared into New Orleans. After the Army Corps tamed the Mississippi in the 1940s, the wetlands, deprived of the river's sediment, began to sink below sea level. Their health further deteriorated as extensive canals were dug, first to explore for oil and gas and then to pump them out. Adding insult to injury, a beaver-sized rodent called the nutria, introduced in the 1930s for its fur, turned out to have a voracious appetite for marsh plants. All told, more than 4000 square kilometers have been lost since 1950.
Faced with damage to marshes as well as impacts to wildlife, politicians began to address the problem in the 1960s. But despite many commissions and reports, there was little action until 1990, when federal legislation channeled about $50 million a year of funds to the state of Louisiana. Some 120 restoration projects are currently active, from hunting nutria to building new marshes with dredged silt. But these projects are small and piecemeal.
After years of debate, in 1998, a coalition of state, federal, and local officials finally settled on an ambitious blueprint for reclaiming the coast. Called Coast 2050 (Science, 15 September 2000, p. 1860), it would have cost $14 billion over 30 years.
Notably short on details, the proposal had the lofty goal of creating a "sustainable ecosystem that supports and protects the environment, economy, and culture of southern Louisiana." It won broad support, with 20 coastal parishes signing off on the concept.
But when the Army Corps presented its implementation plan to the Bush Administration in 2003, the White House balked at the cost. The corps was sent back to the drawing board with instructions to come up with something more modest to show that restoration was feasible. That irked leading restoration proponents, such as Robert Twilley of Louisiana State University (LSU) in Baton Rouge, who feel they already have the know-how to ramp up. "The science is there," he says.
It is this scaled-down version, called the Louisiana Coastal Area (LCA) study and released in November 2004, that the state and the corps asked NAS to evaluate. Weighing in at a more modest $1.9 billion over 10 years, the LCA plan would spend $864 million on five major projects, some already in early stages of operation, and another $762 billion for 10 smaller projects that haven't been as fully designed, among other things.
The NAS committee gave a thumbs-up to four of the five major projects, saying they were well conceived and technically feasible. These four included three sediment-diversion projects analogous to Davis Pond and an effort to restore an eroding headland and barrier island.
But, reflecting long-held concerns among the scientific community and environmentalists, NAS politely suggested the Army Corps "reconsider" a fifth project, a plan to reinforce a major navigational canal, called the Mississippi River Gulf Outlet (MRGO, known as "Mister GO"). Dredged in 1963 to shorten the distance that ships have to travel to New Orleans, this 122-kilometer-long canal was widely faulted post-Katrina for making the city more vulnerable to flooding. Paul Kemp of LSU says that computer models suggest that it and other canals helped channel storm waters into New Orleans and surrounding parishes.
MRGO has also been "an environmental nightmare," says Donald Boesch of the University of Maryland Center for Environmental Science in Cambridge, who was on an earlier technical review committee for the corps. NAS noted that the canal has allowed waves to erode 81 square kilometers of wetlands over the past 40 years. By ferrying in saltwater, it has killed marshes and cypress swamps, too.
NAS stopped short of recommending that MRGO simply be filled in, which John Day of LSU and many other scientists recommend. But it advises against spending $100 million to reinforce the shorelines, as the LCA proposal suggested. "We felt that that was probably not the best use of the available funds," Dean says.
Missing game plan
The main problem with the LCA study is that it is "too modest an effort," NAS concluded. By the corps' own calculations, the LCA study plan would slow the overall rate of land loss by only 20%, to 22.3 square kilometers per year. "It just isn't up to the massive deterioration of the Mississippi Delta," says Day.
A second criticism is that the five projects are spread out across the state. The report speculates that "small projects [were] selected in order to navigate through the political obstacles that might derail efforts if focus is shifted to larger, more significant projects." Although this may have political appeal, it's not a strategic approach that would place major projects in critical places where they would build on each other. Says Boesch: "You have to ask: What's the game plan?"
The Army Corps also needs to think bigger, the panel concluded. "There should be bolder, long-term sediment-delivery projects than were put forth in the [LCA study] plan," says Dean. In particular, NAS detailed two projects that state and federal authorities should consider for greater study. One would divert the final reach of the Mississippi River westward, abandoning the so-called Bird's Foot Delta. The committee couldn't say how much land this would create--in principle quite a bit--or how much it would cost, because the corps has not evaluated the concept.
But, acknowledging the complexity of the undertaking, the committee also detailed the substantial side effects of this project. It would require the construction of a new navigational entrance to the river, for instance, and might also threaten the Delta National Wildlife Refuge and oil infrastructure in the delta.
The other project would divert water from the Mississippi River from a point about 100 kilometers upstream of New Orleans after building an 88-km-long channel to carry the flow to Barataria and Terrebonne Basins, just west of the Mississippi River. Depending on how much water flows through, this could create (or prevent the loss of) 28 to 56 square kilometers of land per year. Before any of this could happen, the Army Corp would have to buy much real estate for the canal and figure out how to compensate farm owners and others whose lands would be flooded. NAS raised the prospect of decades of legal challenges from property owners that "could prove insurmountable."
Gusher. Pumping sediment through pipelines can create tracts of wetlands, but ecologists doubt that the energy-intensive technique is sustainable.
CREDIT: ERIK ZOBRIST/NOAA RESTORATION CENTER
Indeed, NAS didn't downplay the political or biological challenges facing the area. Parts of coastal Louisiana are in such bad shape that trying to fix some wetlands may be hopeless, and communities there may need to be abandoned. Picking which ones will not be easy. What's needed, according to NAS, is a new vision of what the Louisiana coast should look like. Such a map, drawn by federal, state, and local officials, would weigh the societal tradeoffs and chart where wetlands should be restored. Although the ambitious earlier plan, Coast 2050, had many of these elements, says Diane Reed of the University of New Orleans, it didn't explicitly spell out the consequences of the suggested actions, such as diversions changing oyster or shrimp habitat.
It's also important to move quickly from planning to action, scientists say. If barrier islands disappear, waves will strike wetlands with more force. "I'm concerned that if we wait around, we'll jump to a new level of wetland loss," says Greg Stone of LSU. Furthermore, as energy costs increase, some restoration projects, such as dredging or pumping sediment through pipelines, may become too expensive.
The NAS report was almost completed when hurricanes Katrina and Rita hit, focusing national attention on how best to protect the city from future storms. While most of the attention has gone to investigating the failure of the levees (Science, 11 November, p. 953) and options for rebuilding them, many coastal scientists have plugged the role that healthy coasts could play in lessening storm damage. "If we don't restore the coast, any flood-protection system will function less well," says Day. "We can't engineer a system that will protect New Orleans through levees alone."
The report makes a brief nod in that direction: "To the extent that wetlands can offset a significant degree of storm impact, large-scale wetlands restoration projects can be an important component of national efforts to reduce future hazards from hurricanes." The problem, the panel notes, is that there's little empirical evidence of the exact benefit that wetlands provide. An oft-quoted figure is that every kilometer of wetland reduces the storm surge by 7 centimeters, which comes from a few measurements of one hurricane in the 1960s. Better data come from Hurricane Andrew, which suggests that each kilometer of wetlands lowers the surge by 5 cm. Although that again can't be generalized, "there's no question that wetlands are better than open water," Stone says.
Stone simulated a Category 3 hurricane hitting south-central Louisiana. He and his colleagues compared the effects of the storm on the coast, given the extent of wetlands in 1950, 1990, and 2020, if current losses continue. "There was a dramatic increase in storm surge," Stone says. The past 40 years of decline led to a 2.5- to 3-meter increase in the height of storm surges, he says.
Even so, Reed says, it's unlikely that wetlands restoration would have done much to lessen the brunt of Katrina or Rita. "A really big storm is still a really big storm," she says. Given the lack of evidence, Reed, for one, cautions against trying to persuade Congress to foot the restoration bill on these grounds. Levees will remain a key defense.
The importance of wetlands restoration, she and others say, is to ensure that coastal communities are still worth defending. And as the marshes go, so do habitats for oysters, shrimp, and fish that make up an industry valued at more than $3 billion--and the rich culture of the Bayou. Oil and gas infrastructure and jobs are threatened, too. As the coast slowly sinks and sea level rises, doing nothing means an inevitable retreat from the coast, says Bill Good of LSU: "Ultimately, the consequences are going to be worse than Hurricane Katrina."