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How engineers plan to reshape the Mississippi River delta

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First, the delta needs to shrink to a more manageable size

Katrina's anniversary provides a chance to consider how New Orleans has changed since the storm hit, and how the long process of rebuilding homes and fortifying the city's defenses has progressed. But just down the Mississippi River, the delta where the waterway meets the Gulf was hit just as hard or harder 10 years ago, suggesting the vital wetlands and marshes that protect New Orleans from the open waters of the ocean are rapidly receding (1,900 square miles have been lost in the last century).

How do you re-engineer one of the largest river deltas in the world and extend its lifespan after it's been sinking in slow-motion for decades? Three international teams of top engineers just took a look at the problem as part of the Changing Course Design Competition, an effort to channel expertise from the private sector and inform government planning.

Though their approaches differ, the general consensus of the three winning teams is that, instead of merely engineering our way out of the problem, which hasn't always worked in the past, we need to let the delta shrink to a more manageable size. With the state of Louisiana in the midst of enacting a long-term plan for the region, these ideas may play a role in reshaping what's called the "bird's foot delta," the buildup of sediment that stretches out into the ocean, and eventually change the outline of the state.

"Because so many interest groups and communities are involved here, from fishers and hunters to shipping and energy companies, there's a real will to act," says Stephen Cassell a co-founder of Architecture Research Office and chair of the Van Alen Institute, the group which helped facilitate this competition and research project. "We're definitely at a big crossroads."

The swamps and marshlands of the delta are ecologically significant to the immediate area, but the river is economically vital to the entire United States, a shipping superhighway that run right through the middle of the country. That's why, beginning in the late 19th century, the U.S. Army Corps of Engineers began building levees on the river to funnel silt and sediment towards the ocean and clear the shipping lanes for boats. It's helped keep the river clear for boats, but along with navigation channels and pipelines laid by energy firms, the levee buildup has led to runoff and erosion that has damaged plant life and land at the edge of the river.

"If you look at just the last 50 years in terms of land loss, it's happening naturally," says Cassell. "You can basically prune back the delta by default with no planning, and it'll happen in a way that's destructive, or you can look for the best ways, the most intelligent ways, to create a thriving delta."

The three winning plans by teams from Baird, Moffatt & Nichol and Studio Misi-Ziibi, chosen from 21 entrants, all rely on diversion strategies, combining levees and natural processes to fortify land north of the river's mouth and let parts of the delta sink. It's the civil engineering equivalent of abandoning the front lines and falling back to more secure fortifications.

By concentrating the limited amount of sediment that's reaching the end of the Mississippi further north, closer to New Orleans, these plans would reinforce areas closer to the city ("sediment is gold," says Cassell). While these proposals will likely be studied, with the best ideas cherry-picked and implemented in the state's plan, the research is relevant for land-use decisions in delta areas around the world. With the massive, billion-dollar BP settlement serving as a funding source, this may be the perfect time to reengineer the river.

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