$1 billion cost estimate prompts Louisiana to rethink coastal project

Published: Oct. 3, 2014 at 12:31 AM CDT|Updated: Mar. 4, 2015 at 7:09 PM CST
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Dead oak trees in Lake Hermitage near the planned site of the Mid-Barataria Diversion along the...
Dead oak trees in Lake Hermitage near the planned site of the Mid-Barataria Diversion along the Mississippi River

Louisiana is re-examining its ambitious plans for a major river sediment diversion project to build wetlands, based partly on costs that could top $1 billion, according to the state's No. 2 coastal official.

The Mid-Barataria Sediment Diversion Project, planned for an area about 20 miles south of Belle Chasse, would amount to the first large-scale effort to build thousands of acres of land.

However, design work for the project has ground to a halt recently.

"Knowing what I know, I'm hoping diversions are part of the process," said Kyle Graham, Executive Director of the Louisiana Coastal Protection and Restoration Authority.

While the project, part of the state's Coastal Master Plan, had been estimated to run about $300 million, early design work indicates a price of $500 million to $1.2 billion, depending on the methods used.

Graham said the state was now examining four possible sites, two on each bank of the river, including Mid-Barataria.

The concept involves punching a hole in the Mississippi River levee, diverting a portion the river flow into the marsh and mimicking the forces of nature that built the Mississippi River Delta over the centuries.

Pulling off that feat involves complicated science and challenging engineering feats never before attempted.

At 75,000 cubic feet per second, the proposed diversion would fill five to seven backyard swimming pools per second.

"There are absolutely options that if we wanted to spend a billion dollars on this structure, we could," Graham said.

Among the many obstacles, a diversion must be designed to flow under Louisiana Highway 23, and possibly under a proposed future rail line. The state would also need to acquire the land rights.

However, early design work shows the potential costs escalate given the overall size of the structure and the make up of the soils.

"It's a very large, heavy structure that you're thinking about anchoring in some very weak soils."

The most expensive option would involved building the diversion "dry," in some sort of coffer dam-- the type used for many parts of New Orleans new flood gates constructed in the wake of Hurricane Katrina.

Graham said the state hopes to use a less expensive option, building huge parts of the structure off site and floating them into place.

The diversion could also be reduced in size to 30,000 cfs, Graham said.

"Can we do more with less? In other words, do we need that amount of cfs?"

While some coastal scientists have argued over the years that massive diversions were required to capture sediment, Graham said computer models reveal "there's plenty of sediment" in the river.

The state is working together with the U.S. Army Corps of Engineers on a $12.5 million hydrodynamic study of the Mississippi River to find the best spots for diversions.

Graham said the study reveals that coarser material, important to land-building, takes hundreds of years to migrate down the river to Louisiana.

Considering four sites for diversions, instead of examining Mid-Barataria in a vacuum, allows for the use of more sophisticated computer models and analysis of how the diversions affect one another.

Taking silt out of the river in one spot might produce different results downstream.

Graham said the models will provide the state "a package that we would be able to move forward with if, indeed, it looks like we should move forward with them."

As for whether the cost estimates for Mid-Barataria portend similar issues at other sites, Graham noted the state has not done the cost-benefit analysis.

Since planning, engineering and design of the project is expected to take at least 7 years, state officials believe a six- to 12-month pause in the design work could produce a better result.

"Hey, it's smart for us to take a step back," Graham said. "If we get to the end of this and it doesn't look like it's a practical solution, it's not a practical solution."

Diversions have drawn increased criticism over the last couple years, especially from commercial fishermen who fear diverting massive amounts of fresh water into the marsh will dramatically alter salinity levels.

While critics argue for a greater use of dredging to build land by pumping sediment through pipes, state officials counter diversions offer the best hope of building and sustaining larger amounts of land over the long term.

Without widespread use of diversions in the state's coastal tool box, scientists have warned Louisiana would end up with a much smaller footprint of wetlands, maintained at a significantly higher cost.

In the Lake Hermitage area of Plaquemines Parish, the state is wrapping up work on a 653-acre dredging project.

In about 20 years, Graham noted "at least 30 percent of it will be gone."

While the design work is challenging, state officials believe the first of the big diversions could carry the highest price per acre of land.  Future projects could benefit from lessons learned on the first sediment diversion.

As for whether the state remains committed to diversions, Graham remains hopeful, but added, "I don't think you'll see us forcing our way through the process because we said we're going to build diversions."

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