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This story is second in a two-part series on Louisiana’s rapidly disappearing coastline. Read part 1.

As Brig. Gen Duke DeLuca wrapped up his 32-year career with the U.S. Army Corps of Engineers in August, he contemplated the key to Louisiana’s massive, 50-year, $50 billion effort to prevent the southeastern portion of the state from being swallowed by the Gulf of Mexico.

DeLuca, an expert on the many threats facing the coast, said: “It will take a moon-shot type of investment in the science.”

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Many in Louisiana’s coastal scientific community believe DeLuca’s description is right on the mark, capturing the undertaking’s daunting uncertainties.

The mission could not have been set on a more challenging landscape, at a more inopportune time.

Southeastern Louisiana might best be described as a layer cake made of Jell-O, floating in a swirling Jacuzzi of steadily warming, rising water. Scientists and engineers must prevent the Jell-O from melting — while having no access to the Jacuzzi controls.

The problem is human-made. Over the last 80 years, Louisiana’s coast has been starved of sediment by river levees and eviscerated by canals dredged for oil and gas extraction. Now, southeastern Louisiana is sinking at one of the fastest rates on the planet as the Gulf is rising.

Already, 2,000 square miles have sloughed into the Gulf. Without action, the state could lose another 1,750 squares miles over the next 50 years.

If that happens, in 70 years New Orleans could be left on a razor-thin sliver of land extending into the open Gulf, battered by storms rolling over the watery graves of unprotected communities.

The economic effects will reverberate across the nation as the seas swamp half of the nation’s refineries and pipelines that transport 30 percent of the country’s oil and gas. The country’s largest port, an economic door to 31 states, would be vulnerable to run-of-the-mill tropical storms, causing shutdowns that cost the nation’s economy an estimated $300 million a day.

Louisiana has responded with the Master Plan for the Coast, an unprecedented effort to build and preserve up to 800 square miles of wetlands and barrier islands and to construct miles of levees over the next half-century.

At first glance, the plan doesn’t seem complicated: Use the mud and sand in the river to rebuild the delta.

The state has settled on two techniques to do this.

One, pumping sand into sinking wetlands, can build land quickly and is simple to engineer. But it’s a temporary fix.

The other, diverting sediment-laden fresh water from the river, mimics the natural process that built the delta over thousands of years. It could be a lasting solution. But it costs more up-front and will take years to work, if it does.

The plan doesn’t aim to rebuild everything that has been lost so far, or even fight for everything that remains now. Instead, the more modest goal is to restore enough wetlands to cushion communities from storm surge and provide a functioning fishery.

Even that is not a sure thing.

To make the project work, scientists and engineers will have to figure out on the fly how to create a human-made system that replicates the delta’s natural land-building process.

Their solutions must fit within constraints imposed by how much sediment the river can deliver and must anticipate future sea-level rise and land subsidence. Somehow, they must balance the need for restoration with the needs of the shipping, energy, and fishing industries.

Meanwhile, Louisiana must find a way to pay for it. Although this battle has consequences for the rest of the country, so far Congress has spurned most requests for funding. Louisiana, one of the nation’s poorest states, could run out money for coastal restoration in 10 years.

“I don’t think the public realizes just how big a reach this is,” said Harry Roberts, a researcher at Louisiana State University who has spent more than five decades studying the river and the delta.

State legislators acknowledged the challenges by requiring the Coastal Protection and Restoration Authority, which steers the effort, to revise its restoration plan every five years.

“We will adapt as we go along,” said Kyle Graham, executive director of the agency.

If anything, DeLuca’s moon-shot analogy may be an understatement. NASA had to surmount historic scientific and engineering challenges to land a man on the moon. But the existence of towns and cities didn’t rest on the outcome.

“We’ll have to start that on a small scale, and there will be missteps along the way,” said coastal geologist Paul Kemp, a Louisiana State University researcher who has written extensively about the Mississippi River delta.

“But we have to succeed, because this, really, is our only hope.”

Pumping sand into the wetlands

With limits on time, money and what the river can offer, planners had to decide which areas could — and should — be saved.

Most of the rebuilding efforts are concentrated in the basins protecting New Orleans, not only because it’s an economic and cultural center, but because the river already carries land-building sediment through the area.

The first method to restore the coast uses slurry pipelines to dredge mud and sand from the riverbed and offshore, then pump it to sinking wetlands and eroding barrier islands. This approach has been used in beach restoration projects around the country. The state calls it “marsh creation.”

Pipeline projects jointly financed by the state and the federal government already have filled in areas near Bayou Dupont (900 acres, at a cost of $65 million) and Lake Hermitage (700 acres, $40 million), as well as portions of coastal beaches.

But those gains are just a speck of what’s needed in the long-term. With the coast disappearing at 16 square miles a year, it takes nature just two months to wash away as much land statewide as was created in Bayou Dupont and Lake Hermitage.

Another targets the Biloxi Marsh, an isolated section of wetlands on the state’s far eastern edge that protects greater New Orleans and provides a key fisheries habitat. This project would create and restore 33,000 acres of wetlands at a cost of $3 billion.

Slurry pipelines produce results quickly. They can fill 500 acres of open water with land two feet high in six months.

But they have two serious drawbacks. The new land will sink, too, so these areas will have to be rebuilt in 30 to 40 years. And the farther that the sand and mud must be pumped, the more it costs.

Imitating nature

The second method of rebuilding wetlands, controlled sediment diversions, doesn’t have those problems. But one has never been built.

The idea is to move some of the freshwater and sediment in the Mississippi River to where it’s needed most. When the river is high, specially designed gates would be opened in the river levee, allowing freshwater and sediment to wash over nearby areas.

These diversions would build land over decades, not months. Theoretically, they would work as long as the river flows.

“The one advantage this delta has over the many others that are in trouble is that we still have a river delivering the material to help get us out of trouble,” said Denise Reed, chief scientist at the Water Institute of the Gulf. “As long as that river is bringing the sediments to us, we have a chance.”

Sediment diversions cost hundreds of millions each compared to tens of millions for slurry pipelines, but some studies have shown they’re worth it in the long run.

Five sediment diversions are planned to rebuild vast expanses of wetlands in the roughly 60 miles between metro New Orleans and Buras, the last big bend in the river before it meets the Gulf.

The restoration plan calls for spending $4 billion on diversions to build and preserve 300 square miles of land and $20 billion on slurry pipelines that will result in 200 square miles.

What we give up

Regardless of the method, the state doesn’t believe there’s enough sediment in the river to save everything. Wetlands along the last 40 miles to the Gulf, including those near the mouth of the river referred to as the Bird’s Foot Delta, are not in the restoration plan.

These wetlands, already sinking 5 feet a century and far from any large community, will get even less sediment when diversions are opened upriver.

“It is a matter of physics and geology,” said David Muth, director of the Gulf Restoration Program for the National Wildlife Federation. The current plan, he said, “merely proposes not wasting large sums of precious restoration dollars in a place with no future.”

Even some people who are fighting to extend the life of the Bird’s Foot, like rancher Earl Armstrong, acknowledge that reality. Born and raised on the river at Pilottown, nine miles from the nearest road, he now uses airboats to keep an eye on his cattle on the shrinking spits of land.

Armstrong advised the Corps of Engineers a few years ago on the West Bay diversion, the first major effort to build land by cutting a hole in the riverbank south of Venice. His advice was so important, one of the emerging islands is now named after him. But he fears he is fighting a losing battle.

“We probably waited too long to get started,” he said. “I would love for my grandchildren to know what I knew on this river, but it won’t be here. It’s going too quick.”

Mastering a complex game

Although diversions have long been the centerpiece of discussions to restore the coast, the state hasn’t committed to build even one. A decision isn’t expected until fall 2015 because the science and engineering is more complicated than the slogans.

“My concern is that a lot of people think if we just turn the river loose, it will just fill in all those holes we’ve created in the delta,” said Roberts. “Well, certainly it’s not as simple as punching holes in the levees.”

Every diversion project is a move in an ongoing chess match with nature. Each one faces different sets of variables and constraints, and engineers are struggling to anticipate the consequences of each step they take.

“Everything you do at one point on the river — anything you take out or put in — will have an effect on the rest of the river,” said Alex McCorquodale, a University of New Orleans researcher working on a study to determine how much sediment is in the lower Mississippi.

These challenges came into focus as the state began planning the Mid-Barataria Diversion at Myrtle Grove, a $1.1 billion project about 30 miles south of New Orleans. With $275 million in initial funding already in place, it would be the first diversion to be built.

The diversion would be located at the northern end of the Barataria Basin, an estuary important to seafood production and to protecting the New Orleans area from storm surge.

If nothing is done, this area is predicted to lose 234 square miles of coastline over 50 years. Twenty-two square miles of that could be saved over 20 years — if the diversion is fed with enough of the right kind of sediment, flowing over the right wetlands infrastructure, according to computer models.

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The state is still trying to answer the many questions that could make or break those plans.

The first one: Is there enough sediment in the river to get the job done?

Researchers know the river carries only half the sediment it once did. Much is trapped behind dams on Midwestern tributaries, while modern farming methods have reduced soil runoff. They are only now in the final stages of a study to determine if enough reaches the bottom section of the river and if it’s the right type of sediment to build land.

The diversion will be able to deliver 250,000 cubic feet per second, or as much as Niagara Falls at its peak. But computer models have shown that running the diversion at that capacity could increase the risk of flooding nearby communities such as Lafitte.

That, in turn, could force the state to raise the levees around Lafitte. If it costs too much to do that, the state will have to reduce how much water goes through the diversion. Less water will build less land.

High water flows also could hurt fishing.

Louisiana’s commercial and sports fishermen have led the Gulf in catches in a system that has gradually become more salty due to erosion. Now some are concerned that their target species — such as shrimp, oysters, and speckled trout — will be displaced when fresh water pours in.

The Save Louisiana Coalition, a fishing industry group, wants the state to scrub diversions from its restoration plan and focus only on slurry pipelines.

Research is underway to determine how much fishing would be disrupted by operating diversions at different volumes. Planners need to figure out if the amount of land created, and the benefits to storm protection, would offset the economic losses that some fishers say will result.

The vagaries of the river’s flow and geology means you can’t build a diversion just anywhere. It must be on a stretch where the right kind of sands and sediment can be captured, and the open water nearby isn’t too deep and wide to be filled in. There must be enough of the original delta framework to aid in building land. And the wetlands must be built in places where they protect communities from hurricane surges.

Rivers typically build deltas slowly in what looks like a random pattern of constantly shifting channels, islands, and sandbars. To the casual observer “it may look like chaos, to a geologist like me it’s poetry,” said Kemp of LSU.

Recreating that poetry is the key to building land.

“In some of these areas, we did so much damage with the canal dredging, there is really nothing left of that original land-building system — the old channels, and ridges — that the river used to follow,” Kemp said. “We’re starting with basically a blank slate.”

If scientists manage to navigate all of these potential pitfalls, they’ll still need to make sure the shipping channel to the nation’s largest port remains open.

That will limit how much water can be sent to resuscitate dying wetlands. Enough water must remain in the river to allow massive ships to pass.

A recent study concluded that opening just one of the planned diversions at a maximum flow of 250,000 cubic feet per second would dramatically reduce the amount of water left in the lower river. If all five diversions were open at the same time, would they take so much water that shipping would be jeopardized? No one knows.

“Shipping is just one of the constraints we have to consider when we do our modeling,” said Graham, the head of the state coastal agency.

Considering how much remains unknown, a few scientists ask why Louisiana has staked so much on diversions. They worry the state could waste its last chance for the coast on a technique they believe poses its own habitat threats and exists only on computer models.

Gene Turner, a distinguished LSU coastal researcher, points to studies that show high levels of nutrients from fertilizer upstream can cause wetlands loss by damaging plants in areas with high organic soils. He is concerned that the state doesn’t have a backup plan if its computer models are wrong.

“Every building code requires a fire exit, and right now this plan doesn’t have one,” he said. “Saying, ‘This is going to work’ isn’t a backup plan, not when you’re doing something that has never been done before, except on computers.”

Turner has the minority view in the coastal scientific community. Nonetheless, the state coastal agency has asked the Water Institute of the Gulf to gather a panel of outside coastal experts to look into those questions.

“We’ve got one chance to get this right,” Turner said, “so we shouldn’t be ignoring any of these warning signs.”

Sinking land, rising water

Even if Myrtle Grove and other land-building projects pass these tests, other challenges could derail them.

The National Oceanic and Atmospheric Administration says southeastern Louisiana is subsiding at one of the fastest rates of any large coastal landscape in the world.

That sinking isn’t uniform across the area, or year to year, because it consists of several deltas built of different material over thousands of years. So subsidence estimates designed into projects are only best guesses.

“The land here never sleeps. It’s moving in two directions — vertically and horizontally — all the time,” said Stephen Estopinal, a civil engineer who heads the Southeast Louisiana Flood Protection Authority-East, which oversees floodwalls and levees around New Orleans.

Geologists including Sherwood “Woody” Gagliano, who did groundbreaking research on coastal loss in the early 1970s, argue that state planners are not giving enough consideration to the expansive system of underground faults that contribute to sinking land.

Roberts worries the pace of sinking might “make the holes we’re trying to fill deeper than the material we have in the river.”

The biggest wild card is climate change.

The restoration plan accounts for what was thought to be the worst-case projections for sea-level rise. But climate scientists now warn that increases in greenhouse gas emissions and ice field melting couldcause oceans worldwide to rise even more.

That could lead to the river current being slowed as the rising Gulf pushes upstream, further reducing the amount of sediment that reaches diversions on the lower river.

Climate change also will bring volatility in weather worldwide, which could affect projections of how much land can be built by diversions.

To estimate how much water and sediment would be in the river, scientists must rely on records of annual snowfall and rain between the Appalachians and the Rockies. With climate scientists predicting more frequent, severe weather, those averages could become less dependable.

That uncertainty recently made headlines. In 2011, the Mississippi had one of its highest flows ever. Then in 2012, one of the lowest rivers ever reduced shipping traffic to a trickle north of Louisiana.

The sheer size of the challenge facing Louisiana is driven home by an image of Plaquemines Parish that Graham sometimes uses in presentations:

Most of the image is red, showing land lost through 2010. A few tiny spots of green show what his agency has rebuilt in the area.

They look as small and distant as the moon in a night sky.

This story was written by Bob Marshall of The Lens. Data reporting, maps and design by Al Shaw of ProPublica and Brian Jacobs of Knight-Mozilla OpenNews. Photography by Edmund D. Fountain for ProPublica/The Lens.

Additional research by Jennifer Stahl. Additional software development by Jeff Larson.

Additional funding for this project was provided by Knight-Mozilla OpenNews.