Louisiana’s Defense Systems: Wetlands and the Case of the Great Wall of Louisiana

In 2013 the US Army Corps of Engineers (USACE) completed construction of the “Inner Harbor Navigation Canal Lake Borgne Surge Barrier”. The project is funded through the Hurricane and Storm Damage Risk Reduction System (HSDRRS) for southeast Louisiana and considered to be the largest civil works project in corps history. The barrier was built to combat storm surge heights like those observed during Hurricane Katrina in 2005. More commonly known as the Great Wall of Louisiana, engineering innovations like a 1000 foot trestle allowed the project to be completed in about 3 years’ time instead of an estimated 20. The barrier wall is 1.8 miles in distance, 26 feet tall, and at an estimated construction cost of $1.1 billion federally funded dollars.

Louisiana contains 40 percent of the continental United States’ wetland acreage. Coastal wetlands can protect against storm surge energy and flooding by marsh grasses, trees, and soil working as as system. However Louisiana continues to lose wetlands due to problems like subsidence, sea-level rise, sediment deprivation, oil and gas development, and climate change. With an extreme need of wetland preservation, coastal agencies like CWPPRA and USACE are strategizing to combat these issues.

USACE is one of the five managing agencies of the Coastal Wetlands Planning, Protection, and Restoration Act. CWPPRA’s mission is to fund, plan, design, and construct restoration projects in coastal Louisiana at a large and fast pace scale. CWPPRA projects are synergistically funded through partner programs, such as the Inner Harbor Navigation Canal Borgne Surge Barrier to protect, preserve, and restore Louisiana’s coast.

Featured Image Source: https://bit.ly/2MjEIyA

The Mississippi River Deltaic Cycle

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 [1]. 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 [2].

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 [3]. 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.

 

 

[1] https://en.wikipedia.org/wiki/Mississippi_River_Delta

[2] https://en.wikipedia.org/wiki/Great_Mississippi_Flood_of_1927

[3] http://mississippiriverdelta.org/our-coastal-crisis/wasted-sediment/

Image 1 from https://www.nationalgeographic.org/photo/miss-delta-formation/

Featured image from https://phys.org/news/2015-04-future-mississippi-delta.html

Earth Fest at the Audubon Zoo

Folks in New Orleans had no need to wait for Earth Day to celebrate the environment- the Audubon Zoo hosted their annual Earth Fest on March 18, and the Coastal Wetlands Planning, Protection, and Restoration Act was on-hand to discuss the importance of wetlands and wetland conservation in Louisiana. Visitors to the zoo could answer questions at each exhibitor’s booth to collect stamps and win a prize- for those who wanted to test their wetlands knowledge further, CWPPRA staff had the “Wetland Jeopardy” game ready and waiting. Staff also distributed posters from the #ProtectOurCoast series, activity books, and other CWPPRA publications.

This full-day event at the zoo included live music, information on student work, and the opportunity to talk with representatives from Louisiana Sea Grant, the National Park Service, bee-keeping groups, and other organizations with an eye to the environment. Celebrating Earth Fest in March is a great way to remember that environmental conservation, including of wetlands, is not just something for a single day- CWPPRA projects work to protect and restore wetlands throughout the year for the communities, livelihoods, and wildlife that depend on them.

New Orleans Landbridge Shoreline Stabilization & Marsh Creation

Since 1956, approximately 110 acres of marsh has been lost along the east shore of Lake Pontchartrain between Hospital Road and the Greens Ditch. One of the greatest influences of marsh loss in the area can be attributed to tropical storm impacts. Wetland losses were accelerated by winds and storm surge caused by Hurricane Katrina, which converted approximately 70 acres of interior marsh to open water. Stabilizing the shoreline and protecting the remaining marsh would protect natural coastal resources dependent on this important estuarine lake, communities that thrive on those resources, the Fort Pike State Historical Site, and infrastructure including U.S. Highway 90. USGS land change analysis determines a loss rate of -0.35% per year for the 1984-2011 period of analysis. Subsidence in this unit is relatively low and is estimated at 0-1 foot/century (Coast 2050).

Lake Pontchartrain supports a large number of wintering waterfowl. Various gulls, terns, herons, egrets, and rails can be found using habitats associated with Lake Pontchartrain, which has been designated as an Important Bird Area by the American Bird Conservancy. Restoring these marshes will protect the Orleans Landbridge and will help to protect fish and wildlife trust resources dependent on these marsh habitats, particularly at-risk species and species of conservation concern such as black rail, reddish egret, brown pelican, mottled duck, seaside sparrow, king rail, and the Louisiana eyed silkmoth.

Borrow material will be dredged from areas within Lake St. Catherine and Pontchartrain to create 169 acres and nourish 102 acres of brackish marsh. Containment dikes will be constructed around four marsh creation areas to retain sediment during pumping. The lake shorelines will be enhanced with an earthen berm to add additional protection from wind induced wave fetch. Containment dikes that are not functioning as shoreline enhancement will be dredged and/or gapped. Vegetative plantings are proposed including five rows along the crown and two rows along the front slope of the shoreline protection berm, as well as within the marsh platform area.

The project is located in Region 1, Pontchartrain Basin, Orleans Parish, flanking U.S. Highway 90 along the east shore of Lake Pontchartrain and areas surrounding Lake St. Catherine.

This project is on Priority Project List (PPL) 24. This project was approved for Phase I Engineering and Design in January 2015.

The New Orleans Landbridge Shoreline Stabilization & Marsh Creation sponsors include:

• Federal Sponsor: U.S. Fish and Wildlife Service
• Local Sponsor: Coastal Protection and Restoration Authority

Keep up with the progress on PO-169 and other PPL 24 projects.