Barrier Islands provide critical habitat and are the first line of defense to not only day-to-day coastal erosion but also to the destructive forces of major storm events. There remains a critical need to develop cost-effective improvements to existing restoration methodologies that will enhance the successful establishment and spread of vegetation in these important restoration projects. Developing methodologies to enhance vegetation establishment and growth in barrier island restoration projects is important in this very stressful environment because healthy vegetative cover traps, binds, and stabilizes sand and sediment, thereby improving island integrity during storm and overwash events.
The purpose of this demonstration project was to test several technologies and/or products to enhance the cost-effective establishment and growth of key barrier island and salt marsh vegetation. Humic acid and broadcast fertilization regimes were applied. The humic acid amendment and broadcast fertilization regime techniques are intended to “jump start” and facilitate the rapid establishment and expansion of vegetation. Humic acid benefits were demonstrated in both intertidal and supratidal plantings, whereas broadcast fertilization benefits were only demonstrated in supratidal plantings.
Each product (humic acid and fertilizer) is commercially available and off-the-shelf. Enhancing the establishment of woody vegetation (black mangrove and groundsel bush) was achieved via high-density dispersal techniques of propagules and seeds, a cost-saving alternative to planting container-grown transplants. All treatment test sections and reference planting areas were visually inspected and sampled quarterly (plant and soil variables) and compared to the reference area in order to develop recommendations for future planting projects.
This project involved greenhouse studies and the testing of technologies at two previously planted CWPPRA project sites. The CWPPRA projects involved were New Cut Dune and Marsh Restoration (TE-37) and Whiskey Island Back Barrier Marsh Creation (TE-50). Both sites are located in Terrebonne Parish in the Isles Dernieres Barrier Island area.
Gulfside and bayside erosion has resulted in the narrowing of Whiskey Island (and the entire Isles Dernieres chain) as the two shorelines migrate toward each other, resulting in a 68 percent decrease in average width for the Isles Dernieres. Within 100 years, the entire subaerial portion of the Isles Dernieres barrier island system is expected to disappear except for small land fragments associated with the western end of Whiskey Island and the eastern end of East Island. However, some estimates project the Isles Dernieres will disappear much earlier. Other predictions suggest that, without restoration, Whiskey Island could become a subaqueous sand shoal by 2019. Another CWPPRA restoration project, Whiskey Island Restoration (TE-27), which included placement of dredge material, vegetative planting, and sand fencing, was completed in 2000.
The goal of the TE-50 project is to increase the longevity of the previously restored and natural portions of the island by increasing the island’s width. Increasing the island’s width will help to retain sand volume and elevation. Approximately 319 acres of back barrier intertidal marsh habitat, 5,865 linear feet of tidal creeks, three 1-acre tidal ponds and 13,000 linear feet of protective sand dune were created by semiconfined disposal and placement of dredged material. The sediment was dredged from a sediment source in the Gulf of Mexico near the island. The area was planted with native marsh vegetation to colonize and protect the newly-placed marsh soil.
Whiskey Island, one of five islands that make up the Isles Dernieres barrier island chain, is located 18 miles southwest of Cocodrie in Terrebonne Parish, Louisiana. The island is surrounded by Coupe Colin to the west, Whiskey Pass to the east, Lake Pelto, Caillou Boca, and Caillou Bay to the north, and the Gulf of Mexico to the south.
The CWPPRA Task Force approved funding for construction (phase 2) at the February 13, 2008 Task Force meeting. Construction began in March 2009 and initial construction was completed in November 2009.Vegetative plantings were installed at the project site in June of 2010 and October 2011.
The Isles Dernieres barrier island chain is experiencing some of the highest erosion rates of any coastal region in the world. Raccoon Island is experiencing shoreline retreat both gulfward and bayward, threatening one of the most productive wading bird nesting areas and shorebird habitats along the gulf coast.
An existing demonstration project on the eastern end of the island, Raccoon Island Breakwaters Demonstration project (TE-29), has proven that segmented breakwaters can significantly reduce, and perhaps even reverse, shoreline erosion rates. The primary goal of this project is to protect the Raccoon Island rookery and seabird colonies from the encroaching shoreline by: 1) reducing the rate of shoreline erosion along the western, gulfward side and 2) extending the longevity of northern backbay areas by creating 60 acres of intertidal wetlands that will serve as bird habitat. This project has been separated into two construction phases, Phase A and Phase B. Phase A includes the construction of eight additional segmented breakwaters gulfward of the island and immediately west of the existing breakwaters demonstration project and an eastern groin that will connect existing Breakwater No. 0 to the island. Phase B involves the construction of a retention dike along the northern shore to create a back bay enclosure that will be filled with sediments dredged from the bay and/or gulf, followed by vegetative plantings.
The project is located in the Terrebonne Basin on the western-most island of the Isles Dernieres barrier island chain in Terrebonne Parish, Louisiana.
This project was selected for engineering and design funding at the January 2002 Breaux Act Task Force meeting. Construction funding for Phase A was approved in October 2004. Request for Phase B construction funding is anticipated to occur in January 2008.
Water flows downhill naturally and, over time, will make a river change from one path to another. As sediment moved and elevations changed over the last 7 millennia, the Mississippi River has emptied into several historic delta complexes: Maringouin, Teche, St. Bernard, Lafourche, Plaquemines-Balize, and Atchafalaya. Each of the deltas built up part of Louisiana’s coast to what we see today, but now that natural process has been interrupted . After the great Mississippi flood of 1927 that caused $1 billion worth of damages (almost $1 trillion in today’s dollars), the US Army Corps of Engineers built the world’s longest levee system under the Flood Control Act of 1928. The Levee system was constructed to reduce flood damages and allow for more control of the Mississippi .
Image 1: Historic Deltas of the Mississippi River
An unforeseen and unfavorable side effect to taming the river was that all the water is kept moving too quickly to deposit sediment, and now sediment is lost to the Gulf of Mexico rather than deposited into our coastal wetlands . Our Louisiana coastline is dependent on new sediment to nourish wetland ecosystems. Without sediment delivery, there is no material for natural land gain or replenishment, which will continue to contribute to our retreating coastline. The solution is not as simple as removing the levee system, however, since so much of Louisiana is populated now, and removing the levees containing the Mississippi would displace millions of residents from their homes. Instead, CWPPRA and our partners in restoration use man-made systems to create marsh, nourish wetlands, and maintain hydrologic connectivity so that we can protect and restore Louisiana’s coast.
This area is undergoing shoreline erosion, interior wetland
loss, overwash, and breakup. The Gulf shoreline erosion rate
has doubled from 1988 to 2006. Project area marshes also
are being eroded at -11.8 ft/yr between 2003 to 2006 as well
as being converted to open water from internal breakup.
Restoration would expand the Gulf shoreline structural
integrity and associated protection by tying into two recently
constructed projects to the east and address one of the
remaining reaches of the Barataria/Plaquemines shoreline.
The design includes fill for a beach and dune plus 20-years
of advanced maintenance fill, as well as fill for marsh
creation/nourishment. The location of the type and amount
of sediment needed to construct this project already has been
identified under the East Grand Terre Project that is presently
under construction. Approximately 127 acres of beach/dune
fill would be constructed and approximately 259 acres of
marsh creation/nourishment would be constructed. Intensive
dune plantings would be conducted by seeding and installing
approved nursery stock. About half of the
marsh platform would be planted with cordgrass and
portions of the dune, swale, and marsh would be planted
with appropriate woody species. Containment dikes would
be breached no later than year three to allow tidal exchange
with the created marsh.
The project is located in Region 2, within the Barataria Basin
portion of Plaquemines Parish.
This project is on Project Priority List(PPL) 19.
The Cheniere Ronquille Barrier Island Restoration project sponsors include:
Barrier islands are known as coastal Louisiana’s first line of defense against destructive storm surge. These islands are a unique composite of beach, dune, marsh, and sand flats that host a tremendous variety of fisheries and wildlife, including endangered species. Barrier island restoration projects are designed to protect and restore the features unique to Louisiana’s barrier island chains. This type of project may incorporate a variety of restoration techniques, such as the placement of dredged material to increase island height and width, the placement of structures to protect the island from erosive forces, and the placement of sand-trapping fences, used in conjunction with vegetative plantings, to build and stabilize sand dunes.
Responsible for the majority of Louisiana barrier island restorations to date, CWPPRA has led the charge in barrier island restoration because it recognizes the ecological importance of barrier islands and their critical role in the defense of coastal Louisiana.
Since 1930, Louisiana has lost 1,900 square miles of wetlands. That is enough land to equal the size of Delaware.
The Coastal Wetlands Planning, Protection, and Restoration Act is fighting land loss by utilizing several restoration techniques for land preservation and creation. Some of CWPPRA’s restoration techniques include: