ONGOING EROSION DURING CONSTRUCTION (Image courtesy of HDR Engineering Inc.)
The constantly eroding shoreline was perhaps the greatest recurring challenge of the project. Anytime there was appreciable downtime for weather or other issues “that caused delays in getting the armor rock down, the shoreline going to the west continued to erode,” says Geesey. New surveys had to be conducted every few months throughout the construction phase.
Initially the plan was to conduct new surveys every three months, says Trosclair, but “you really had to get it in much quicker so you could get (the work) established before there was another change.” That meant the time frame was closer to new surveys every two months. “The contractor came up with an assembly-line-type procedure to get the rock installed as quickly as they could,” Trosclair adds, “because the landscape was changing so much.”
Settlement plates — metal poles installed in the breakwaters — will be used by surveyors to periodically measure the LWAC structures for settlement, notes Broussard. And the shoreline will be monitored for any accretion of new land from sediment captured by the breakwaters. Such accretion has already begun “pretty much everywhere (the breakwaters) were constructed,” says Barringer.
In fact, the breakwater project is working so well that Trosclair first noticed improvement during the demonstration phase. Sediment “actually built up enough (behind the LWAC demonstration structure) that you could walk from land and touch the rocks, where before there had been 3 ft of water,” he says.
And the sediment buildup is continuing behind the completed LWAC breakwater segments. Much of the new material is still shell hash, Trosclair says, but he is also starting to see silt and sand collecting behind the breakwaters. Together, these new materials are “becoming more stabilized, more compact,” he notes. “It’s not as loose as it had been before the shoreline protection.” Moreover, he adds, “We’re seeing vegetation beginning to establish, and the shell hash is actually building up in elevation and not moving.”
The sediment buildup is a welcome side benefit of a program that was primarily focused on just stopping erosion, says Geesey. Moreover, the success of the LWAC breakwaters was both fortunate for the refuge and a nice change from prior experience. “In the past, many breakwaters constructed in Louisiana left a bad taste in people’s mouths because they settled so much,” explains Barringer. “After they settle under the water, they become more of an obstruction that doesn’t do anything to protect what it’s supposed to protect. So the fact that we were able to come up with this (LWAC) approach, I think, will hopefully make this type of hard structure a little more feasible in the future.”
Additional projects funded by Cameron Parish and others are already planned, including an effort under construction to extend the breakwaters about 3,000 ft to the west. The existing LWAC system has stood up well to the various hurricanes that struck the region this year, although at press time a survey was planned to confirm that assessment.
Rockefeller Wildlife Refuge manager: Louisiana Department of Wildlife and Fisheries
ME-18 project federal sponsor: National Marine Fisheries Service
ME-18 local sponsor: Louisiana Coastal Protection and Restoration Authority
ME-18 project managers: Louisiana Coastal Protection and Restoration Authority and the National Marine Fisheries Service
Lead designer: HDR Engineering Inc., Lafayette, Louisiana office
General contractor: LeBlanc Marine LLC, now part of Patriot Construction and Industrial LLC, Duson, Louisiana
This article first appeared in the January/February 2021 issue of Civil Engineering as “Protecting a Refuge.”