While much coastal restoration effort concentrates on building back marsh that’s washed away, it’s much more effective to prevent the loss in the first place.
That’s just what a series of projects in Vermilion Parish, some dating back 20 years, aims to do. Rock walls along the shoreline at Freshwater Bayou, including some built earlier this year, act as a bulwark against the onslaught of waves that can break down the marsh and quicken the process of erosion and land loss.
“Boat traffic that comes down here creates massive waves that erode the shoreline,” said Chris Allen, project manager with the state Coastal Protection and Restoration Authority.
At the same time, the state is nearing completion of a $3.4 million project to restore the marsh behind the rock wall. Sediment is dredged from the bayou and pumped over the rock and into the marsh area. More than 100 acres of marsh are expected to be built by early next year using a combination of state surplus funding and state Department of Natural Resource funds, including money paid by companies to make up for wetland impacts elsewhere.
The rocks help prevent salt water from being carried into the fresher marsh behind it, Allen explained. Salt water from the Gulf of Mexico breaks down organic soils of the fresher marsh area, then the tidal action takes that land back out with the tide.
Keeping the salt water and the tidal action out of the marsh helps keep what land is already there in one piece. Building additional wetland acreage serves a similar purpose by helping to keep salt water and tidal action from working into the interior marsh in the area, Allen said.
The rock walls are an option against coastal erosion in sections of west Louisiana’s coast because the soil is firmer than the soil found to the east.
“We’re fortunate over here with the soil. You can build things and they’ll stand up,” said Mel Guidry, construction manager with CPRA. In southeast Louisiana, he said, these types of hard-protection structures sink out of sight in the soft mud in a matter of years.
The proof is easy to spot riding down Freshwater Bayou. Rock placed in the 1990s is almost indistinguishable from the 33,000 linear feet built earlier this year.
The almost $12 million project, paid for through state and parish Coastal Impact Assistance Program and completed in June, put rock shoreline protection along four sections of the bayou.
“We can place rock where it’s effective and we do, but we can’t just rock the entire coast,” said Chuck Perrodin, public information officer with CPRA.
Previous construction projects in the Freshwater Bayou area, some launched as far back as 1994, included not only the rock along the shoreline but also backfilling a pipeline canal, building terraces to trap sediment, construction of oyster reefs to reduce erosion and the placement of breakwaters along the shoreline.
Two other projects for the area that are being designed for possible future construction through the Coastal Wetlands Planning, Protection and Restoration Act include building and nourishing more than 400 acres on the west bank of Freshwater Bayou and another 418 acres of wetland creation.
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