When a fast moving stream meets a still or slowing moving body of water, it almost comes to a halt and deposits the sediment it is carrying in the still body of water. This is how the Mississippi built the Louisiana Coast over the last 7,000 years. When the river ceases to push the delta front further and further into the Gulf of Mexico, the delta front, the headland, begins to deteriorate and transform itself into barrier islands. In time the barrier islands themselves are reduced to sandy shoals under the gulf. Such is the case with Ship Shoal, Trinity Shoal, and the St. Bernard Shoals.
“Louisiana’s barrier islands buffer storm surges, reduce flooding in the bays and erosion in the marshes behind them, and preserve estuarine systems by maintaining the gradient between saltwater and freshwater in the basins they protect. The processes that build barrier islands–waves, tides, and the circulation of coastal waters–also erode and fragment them.”
When the Corps of Engineers and the Louisiana Department of Natural Resources published the Louisiana Coastal Area Ecosystem Restoration Program in 2004 and Congress approved it in the 2007 Water Resources Development Act, one “near-term critical feature” of the plan was the restorationof the Caminada Headland, the delta front of the Mississippi that flowed along Bayou Lafourche, which would protect oil and gas infrastructure at Port Fourchon, located on the headland. It also might prevent more land loss in the Barataria Basin, which has already suffered quite a lot of land loss.
Gov. Bobby Jindal wants to build ersatz barrier islands (a project that looked intriguing a month ago, but on second thought not) out front of the Caminada Headland and Barataria Bay, which is already seeing BP oil spoiling Queen Bess Island, a pelican nesting colony the state established in 1968, when it looked as though the Brown Pelican was going to go extinct in the state of Louisiana. But where is he going to get the sand?
According the LCA program the state already has dibs on the sand at Ship Shoal, the sandy, underwater remnant of an ancient Louisiana delta that was active 7,000 years ago.
With permission from the Minerals Management Service the Corps and the DNR would mine between 9 and 10 million cubic yards of well-graded quartz sand from Ship Shoal to beef up thirteen miles of shoreline. In essence they would build 529 acres of dune to the existing 430 acres of dune on the headland to bring it to a total of 959 acres of dune.
A similar beach reconstruction project started on East Grand Terre Island in 2009, where sand dredged from the floor of the gulf is being pumped to the island, spewed onto the beach, and spread by bulldozers. Perhaps, this is the model for Gov. Bobby Jindal’s ersatz barrier islands. The project will restore 2.8 miles of barrier shoreline with a 6-foot dune, build a 450 acre marsh platform behind it, install sand fencing, and anchor it with vegetative plantings, all at a cost of $36,705,731, which gives you an idea how far the $360 million Jindal hopes to get from BP for his barriers will go.
So suppose Gov. Jindal takes his sand from Ship Shoal and builds his barrier islands. What will happen to them? Again, look to the projected fate of the reconstruction of dunes on the Caminada Headland as outlined in the LCA Study:
The LCA study points out that 49 acres of carefully designed and constructed sand dunes would be lost to erosion and sea level rise within the first year. The 959 acres of dune would be down to 750 acres in ten years, and the state would have to cart in 2 million additional cubic yards of sand to bring the dunes back to 910 acres. In short restoring beefing up the Caminada Headland would be an endless process and much would still be lost to erosion and sea level rise.
The U.S. Geological Survey has a lengthy description about where the sand could come from and what will happen to Gov. Jindal’s poorly designed and hastily constructed ersatz barrier islands to stop BP oil from invading and destroying coastal marshes. They would begin to erode away in the first big storm and a really big storm would simply carry the oil over them.
Mining the sand for Jindal’s berm gulfward of the Caminada Headland and other barrier island would create a pit into which nearshore sand would fall, hastening the erosion of the barrier island behind the berm, because wave wash does deliver sand to the barrier islands, especially in the summer when the gulf is fairly calm–hurricanes excepted.
The berms out front of Barataria Bay would required 36 million cubic yards of sand that would be washed away, useless for restoring the Caminada Headland.
Louisiana is in a pickle. A year ago two Louisiana State University scientists published a paper that stated there is not enough sediment remaining in the water column when the Mississippi flows pass the Louisiana marshes to rebuilt the marshes. It is all trapped behind headwater dams, built to retain floodwater in the uplands until a flooded Mississippi can handle it. Louisiana cannot waste a single cubic yard of sediment–sand or silt. It’s too hard to come by. LaCoastPost had a discussion of this issue at the beginning of the week.
What to do about the BP oil? It’s a mystery.
Update, July 12, 2010: Well, that didn’t work. Len Bahr at LaCoastPost has images of Bobby Jindal’s sand berms, built to protect the Chandeleur Islands from oil. They washed away in the rough seas of the last several weeks.
© 2010, Quinta Scott, All Rights Reserved.