Sustaining Rebuilt Coastal Marshes
Dr. Robert Twilley, LSU Oceanic Studies professor and director of the Louisiana Sea Grant program, it’s time to rethink the premises upon which Louisiana is basing its coastal restoration projects.
"I doubt those marsh creations are going to have more than a 20-year lifecycle without modifying the way we manage the river," he told members of the Governor’s Coastal Advisory Commission Tuesday.
Twilley says there’s a flaw in the premise of many of these projects: the idea of recreating a “natural” ecosystem.
"All of our ecosystem restoration projects are being designed in landscapes that are highly engineered. We’re not building natural systems back to where they were.”
The engineering he referred to is the Mississippi River flood control system – the levees, primarily, which force the river to move up instead of letting it flow out.
"Flooding is a fundamental process that built this land," he explains, even giving the mathematical formula for river-borne land creation: Ltop= Qsfr (1+rorg) / [C(σ+H)]
"It’s the laws of physics. It’s based on input – sediment; and the losses – which are a function of sea-level rise and subsidence."
Currently, he says, the result of the equation is a negative number.
"We’re making a huge investment in marsh creation, but we’re doing it in a sediment-starved landscape."
Twilley says so much of the Mississippi River flood control infrastructure was built following the 1927 flood, and it’s nearing the end of its lifespan. He urged commission members – several of whom are also members of the Coastal Restoration Authority — to reach out and partner with the Army Corps of Engineers as they plan for levee improvements.
"You know, there’s a lot of thinking going on, as far as reinvestments that need to be made in that infrastructure. There are opportunities to modify the flood control responsibilities of the federal government, to incorporate our needs in ecosystem restoration."