Decades of draining, dredging and other mistreatment have taken a severe toll on Louisiana wetlands. Hurricane Katrina focused a spotlight on the need to restore the marshes, which can lessen the risk of water surging toward New Orleans. But any such plan would have to compete for money with other flood protection projects, such as raising levees. Results of new model, unveiled here yesterday, may help win support for repairing the wetlands.
Louisiana wetlands face extreme challenges. Sea level is rising and the ground is sinking, both of which threaten to drown the marshes. Normally, sediment deposited by the Mississippi River helps build up the delta, allowing the marshes to stay above water. But engineering of the river to make it better for shipping has caused much of its sediment to flow into deep water.
One proposal to fix this is to divert river water out of the main channel so that it flows closer to shore. As sediment gets dumped there, it would build land that would turn into wetlands. It's never been clear exactly how much land would be created, however. That makes it harder to sell the concept to politicians, says ecologist Robert Twilley of Louisiana State University.
So Twilley teamed up with geoscientist Chris Paola of the University of Minnesota in Minneapolis and others. About 15 years ago, Paola helped design a computer model that predicts how rivers create deltas. It has been used extensively to help mining companies figure out how sediment from tailings will fill up their storage ponds. With conservative assumptions about sea level rise and the subsidence of the area, two diversion structures—large concrete sluices placed in the river embankment--would create about 700 square kilometers of land over 100 years, said Gary Parker of the University of Illinois, Urbana Champaign. If sea level rises more slowly and land sinks less, the structures would build up 1000 square kilometers off the present coast.
"This is the largest and most aggressive element of a comprehensive plan," Twilley says. It would cost perhaps $500 million a year to build and operate. He hopes that the new analysis will convince state legislators of the importance of the project. "They are going to have to put this in the top basket. I feel confident that the state will do that."
Denise Reed of the University of New Orleans agrees that the project is a good idea and that the new analysis may help win support for it. "This is pretty crucial information," she says.
--Erik Stokstad
Oops--my bad! The model predicts land formation over 100 years, not 30 years. It's the cost--estimated at $15 billion--that would be spread out over 30 years. We've corrected the story here and on ScienceNOW.
The presenters plan to submit a paper soon on the results and assumptions of the model. Stay tuned.
Seven hundred square kilometers in 30 years is more than any other model has ever predicted. What model is this, and what assumptions and inputs went into the model?
Being able to quantify the benefits of restoration projects is great, but overstating those benefits will only harm future implementation of projects.