Researchers clash over whether freshwater diversion is helpful or harmful to coast

Standing on a crude wooden boardwalk and wielding a 5-foot-long shiny metal instrument called a Russian peat corer, Theryn Henkel drives its spear-like end deep into the marsh of the Davis Pond freshwater diversion on the west bank of St. Charles Parish. 

Henkel, a coastal resources scientist at the Coastal Protection and Restoration Authority (CPRA), turns the T-handle and slides the instrument out of the muck to reveal a core sample with cake-like layers of grassy, organic matter and river sediment – a sign of new land growth.

Originally authorized by the Flood Control Act of 1965 to help boost oyster production in the region, by the time Davis Pond diversion opened in 2002 its purpose shifted to focus on fighting saltwater intrusion from the Gulf of Mexico. It was never intended to build land. 

“So we’re a little over 4 miles from the diversion, as the water flows, and we’ve got a foot of deposition from a diversion that was never supposed to build land,” Henkel said. She pointed to stands of willow trees and the dark, sludgy river sediment as clear signs of growth. 

“Imagine what we could do when we start really targeting this,” she said.

Some scientists and state agencies say freshwater diversions are the key to saving Louisiana’s rapidly eroding coast. To that end, the state is expected to spend more than $2 billion on projects such as the Mid-Barataria Sediment Diversion, a massive freshwater diversion that will redirect Mississippi River water into the Barataria Basin. 

Others argue data may not support diversions as the best option, and they say the risks to habitat and wildlife — and the jobs they support — aren’t worth it when cheaper alternatives may be more effective.

Stepping off the boardwalk in Davis Pond, his white New Balance shoes squelching in the damp soil, John White, associate dean of research and a professor at LSU’s Department of Oceanography and Coastal Sciences, approached Henkel’s core sample to pull off a chunk of the sediment layer. Louisiana has some of the highest sea level rise in the world, about 3 to 3.5 millimeters per year, White said. On top of that, the land is also sinking up to 10 or 11 millimeters in some places. 

“So that difference is a sea level the rest of the world is going to see in about 50 to 60 years – those problems that we’re having here on our coasts are coming for everyone else,” White said. The land-loss solutions developed in Louisiana will help inform coastal communities across the globe, he said. 

“We’re the canary in the coal mine,” White said.

White, along with researchers Brady Couvillion and John Day, recently published a paper that looked at two freshwater diversions: Davis Pond and Caernarvon, which lies down the Mississippi River just south of Violet in St. Bernard Parish. The study found that over the past two decades, Davis Pond built just over 1.3 square miles of new land where the water flows into Barataria Bay. Caernarvon has had “no statistical effect on the land change.” 

The study concluded that freshwater diversions can build new land or at least not have a negative impact on the land. State officials are pointing to the paper as confirmation for the efficacy of diversion projects. 

But a 2019 study by Eugene Turner, another LSU researcher and professor, found that diversions may have actually led to land lost, not gained. 

Turner has criticized White’s paper, saying it doesn’t include reference or control areas for comparisons that would allow the land changes at Davis Pond and Caernarvon to be accurately assessed. 

“They have one measurement before and after the Davis Pond, and a before and after for the Caernarvon area. But that doesn’t tease apart the effects of things for the whole area,” Turner said.

Turner said he doesn’t dispute White’s land change measurements; he challenges the cause of that change. 

“It might have happened without the diversion. It might be happening around that area anyhow,” he said. “To claim that the diversion did that just doesn’t make sense.” 

Additionally, Turner said that even if you accept the paper’s conclusion that the Davis Pond diversion did build new land, the price tag shakes out to around $500,000 an acre, given the cost of the diversion. 

“That’s an incredibly high price,” Turner said.

There’s also the potential impact freshwater diversions can have on local ecosystems, which could be devastating for Louisiana’s seafood industry. 

“All of the economy that’s driven in the state with our seafood industries, it’s all saltwater-related fishing industries, you know, our oysters, our shrimp, our crabs, our speckled trout,” said George Ricks, a St. Bernard-based fishing guide and president and CEO of the Save Louisiana Coalition, a group representing commercial fishing and seafood industries and is opposed to freshwater diversions.

Ricks said the introduction of freshwater from the river into the saltwater basins and marshes of south Louisiana can decimate the wildlife that lives there — from swamp grass to dolphins. 

“Everything relies on this delicate balance in our estuaries,” he said.

Ricks said many coastal communities in Louisiana are “hanging by a thread now,” and that these industries are vital sources of income. Plaquemines Parish is home to the second largest commercial fishing fleet in the U.S. 

“We’re going to lose everything because of these diversion projects,” he said.

Ricks and Turner point to alternatives for land building, such as dredging and backfilling canals, which they say do not harm local ecosystems, have been proven effective and have a clear return on investment. Diversions may or may not work or be worth the price tag attached to the massive projects state officials have planned in the coming decades, they said.

White said he has a new study coming out soon that includes control or reference sites within Davis Pond that also concludes the diversion has been the cause of the new land. “We have the data now to show that,” he said.

Turner and Ricks remain skeptical. 

“We’ll have to wait to see the analysis. I am glad to see the recognition of a need for reference sites — something the first paper omitted,” Turner said. “Science moves forward in what seems like a zig-zag motion at times, but more effectively when words are committed to paper and subject to analysis by others, something that will continue for a while in this case.”