Louisiana is drowning: Over the last eight decades, more than 2,000 square miles of land have disappeared underwater. When engineers sealed off the Mississippi River with levees to prevent flooding in the 1930s, they also cut off the river’s natural process of building land.
Before the river was “channelized”–locked into an artificial path–it curved through the Delta dumping piles of sediment that slowly built up the ground and helped protect cities like New Orleans from storms. Now a new design, called Delta for All, proposes bringing that process back.
“The Mississippi River used to lie on the ground like a fire hose, and it would move and spray water and sediment, and that’s what basically creates the Delta landscape that New Orleans and the communities around it are built on,” says Gina Ford, a principal at Sasaki Associates. Ford was a member of the Baird Team, led by Baird & Associates, one of the winning teams that competed in Changing Course, a recent competition that asked engineers to rethink how the Delta might be saved.
Louisiana has a multi-billion dollar Coastal Plan that includes some interventions to stop sediment from shooting straight into the Gulf of Mexico. But when the Baird Team crunched the numbers, they saw that the plan could only capture 25% to 50% of sediment. Their new proposal looks at how to capture it all–knowing that even that won’t be enough to fully save the landscape.
“Even if you capture every grain of sediment that comes down the river, you still can’t build enough land to sustain the entire Delta as it exists today,” says Ford. “That starting point, of saying this is the kind of land loss we’re looking at, sets up the need for a much bolder and bigger solution.” An interactive map on their site shows how much more land can be saved the more sediment is captured.
Their suggestion: Building a series of faucet-like gates along the river that could be turned on and off to let sediment naturally spread, in a controlled way. “Over the next hundred years you can imagine opening the river up in a basin, letting it run for a while, capturing as much sediment as you can, doing it again in another basin, and kind of cycling through the basins to try to capture as much land as possible,” she says.
By letting the river flow out at strategic locations, the plan would also help the river from overflowing its banks in New Orleans. “If the river is opened up into one of these basins, all of the sudden the river elevation would drop,” Ford says. “It drops it enough that the city’s flood risk reduction is improved by eight times as much. Because all of the sudden the river is no longer as high, so when it floods, it doesn’t get as high with floodwater.”
That, in turn, could save New Orleans from spending billions of dollars on future flood damage; the benefits are similar to making levees five feet higher in the city and nearby communities. The plan could also avoid another $2 billion to replace new locks and half a billion to replace the Bonnet Carré Spillway. It would also make navigation easier for large ships.
At this point, it’s just a concept–but one the engineers hope the state considers. The Environmental Defense Fund is currently working with the state to evaluate the different designs from the competition and see what might be possible to include in a 2017 update of the master plan.
It’s also a solution that could work elsewhere. “We’re creating a strategy here that could really become an international model for how to deal with sea level rise,” Ford says. “Many of the major cities and ports in the world are in river delta locations, where there’s an issue of resilience and storm surges. If New Orleans goes big and bold, and sets a different course for the next 50 years, it really could become a model for the world.”