Update on the LaBranche East Marsh Creation Project

Project Summary:

The LaBranche Wetlands ecosystem contains the largest contiguous tract of wetlands along the south shore of Lake Pontchartrain (Figure 1).  The area contains approximately 20,000 acres of tidally-influenced marshes and cypress swamps.  Interstate 10 (I10) passes over the intermediate/brackish marsh of the LaBranche Wetlands between the Jefferson-St. Charles Parish line and the Bonnet Carré Spillway, making it one of the most highly visible wetlands in our area.

The primary goal is to restore marsh that converted to shallow open water. Project implementation will result in an increase of fisheries and wildlife habitat acreage, and diversity along with improving water quality. The proposed project would provide a protective wetland buffer to the railroad and I-10, the   region’s primary westward hurricane evacuation route, and complement hurricane protection measures in the area. The proposed solution consists of the creation of 1471 acres of emergent wetlands and the nourishment of 148 acres of existing wetlands using dedicated dredging from Lake Pontchartrain. The target elevation of the marsh creation cells is the same as average healthy marsh adjacent to the project area. The creation cells will be fully contained.

How It All Started…

The construction of the Illinois Central Railroad, cutting through the LaBranche Wetlands, was the first in a series of human-induced changes to the LaBranche Wetlands that caused significant negative impacts to the wetland ecosystem. In the 1950’s, an open water pond formed in the northwest corner, due mainly to a failed agricultural impoundment. Dredging of access/flotation canals for construction of I-10 resulted in increased salinity & altered hydrology that exacerbated conversion of emergent wetland vegetation into shallow open water bodies. In 1965, Hurricane Betsy pushed a huge storm surge of salty water into the marsh. The saltwater exacerbated the negative hydrologic effects of the man-made openings in the shoreline to build the interstate. As a result, the open water areas in the LaBranche Wetlands increased from 300 acres to more than 4,200 acres. More recently, Hurricane Georges and the severe drought during 1999 and 2000, dealt another blow to these fragile wetlands. Saltwater impacts caused much of the remaining vegetated marshes to become stressed and die-off. Once the vegetation died, the marshes were very susceptible to erosion and conversion to open water.

USDA/NRCS Early Efforts with Landowners

The Natural Resources Conservation Service (NRCS), formerly the Soil Conservation Service (SCS) has been helping landowners in the LaBranche Wetlands fight coastal wetland deterioration and the subsequent loss of wetland habitat for several decades. In 1985, NRCS, in cooperation with the Crescent Soil and Water Conservation District, finalized a marsh conservation plan to address the natural resource concerns within the LaBranche Wetlands. The plan was permitted by the Louisiana Department of Natural Resources (DNR) and the U.S. Army Corps of Engineers (USACE), New Orleans District.

Conservationists tried several different ways to combat wetland deterioration and land loss. Vegetative plantings were used along shorelines vulnerable to wave erosion due to the increased areas of open water. Rip-rap (i.e. rock armor) was placed along shorelines where wave energy was too powerful for vegetation alone to withstand. Christmas tree fences were built to trap sediment.  Water control structures were installed to reduce saltwater intrusion and manage water levels.  Water control structures were located in openings underneath the railroad tracks and in canals that provided avenues for saltwater intrusion. As required by permit conditions, the Louisiana Department of Transportation LDOTD) and the Federal Highway Commission agreed to the installation of three variable-crest weirs to help mitigate for the construction and maintenance of Interstate 310.  The fight to protect the remaining wetland functions of the LaBranche Wetlands continued as conservationists hoped for ways to restore the severely degraded system. Wetland restoration requires funding and the dollars and restoration techniques were simply not available to restore our vanishing coastal wetlands.

CWPPRA Inception and Broadening Coastal Restoration Efforts

The Coastal Wetlands Planning, Protection, and Restoration Act (Breaux Act) passed in 1990 turned the tide in favor of restoring the LaBranche Wetlands, especially the severely degraded marshes.  Unfortunately, most of the brackish and intermediate marsh had already converted to open water.  In 1994, the first “CWPPRA Project”, PO-17, was constructed in the LaBranche Wetlands.  PO-17, consisting of approximately 400 acres of created marsh was built adjacent to Lake Pontchartrain.  The project is still functioning today and it appears that the created marsh will provide emergent marsh functions for many years in the future.

Working with CPRA State Partners

Since the inception of CWPPRA in 1990, many worthwhile projects have been constructed across the Louisiana coast.  CWPPRA has constructed, or funded for construction, projects to protect and restore over 100,000 net acres (158 square miles) of Louisiana’s coastal wetlands. As of September 2023, 114 projects have been constructed, 26 are currently under construction, and 25 are in engineering and design.  A project must have a federal sponsor to work with Louisiana’s Coastal Protection and Restoration Authority (CPRA).  Project funding is 85% federal and 15% State. Due the numerous projects being funded and constructed through CWPPRA, the LaBranche Wetlands would not get back on the radar until 2010. The CWPPRA Task Force approved the LaBranche East Marsh Creation Project (PO-75) for planning and design (Phase I). Then, in 2012, the LaBranche Central Project (PO-133) was approved for planning and design (Phase I). NRCS, as the federal sponsor for both LaBranche Projects, began what turned into a grueling planning and design marathon.

Challenges

Marsh Creation, even under the best of conditions, is a precarious undertaking.  The LaBranche Marsh Creation Projects seemed doomed from the start of the planning process due to concerns about soil conditions in the project site.  During the preliminary geotechnical analysis in the laboratory, the soils appeared that they lacked the stability to support a newly created marsh platform for an adequate project life.  The created marsh platform was predicted to settle below the threshold required to support a healthy emergent marsh.

In some areas of the Louisiana coast, predicted settlement rates within proposed marsh creation sites may be too excessive to build a marsh platform capable of supporting emergent vegetation.  The soils within a proposed project area must be bored and thoroughly analyzed to predict marsh platform settlement rates and suitability for containment dike construction.  A suitable borrow area must be reasonably close for the project to be feasible. Furthermore, the proposed borrow area must contain soils suitable for building a stable marsh platform and containment dikes.  Based on the initial soil investigations, the LaBranche Marsh Creation Project faced what seemed like insurmountable obstacles.  The preliminary geotechnical investigations suggested that the created marsh platform would sink or settle to an elevation too low to support a healthy emergent marsh.  Based on preliminary investigations, containment dike constructability was risky because some problem areas were identified that might require special construction techniques.

Persistence and Determination

Despite the challenges, the LaBranche Project Team continued to work toward a solution and proposed a pilot project to determine if actual field conditions may warrant, with an acceptable degree of certainty, project construction.  NRCS constructed the pilot project in the summer of 2013.

Marsh platform elevation was recorded in detail including initial fill height and post-construction settlement.  Monthly surveys were conducted for a period of 12 months after construction to measure the rate of settlement over time.  A final survey was conducted in March of 2016 to facilitate the projection of marsh platform settlement over a 20-year period.  Field data from the pilot project was used to augment the existing geotechnical data that was based solely on laboratory analysis.  The original geotechnical investigations conducted for CWPPRA project PO-75 indicated that a created marsh platform, constructed to an initial fill height of +4.2’ elevation, would settle below an acceptable “healthy marsh elevation” within 3 to 4 years.  However, actual field results from the PO-75 pilot project indicated that a “healthy marsh elevation” may be attainable over a 20-year period.

The pilot project demonstrated that it was, indeed, possible to construct a marsh platform to a target elevation capable of supporting emergent plant species.  The pilot study findings and the preliminary geotechnical results were now being considered together to determine the fate of the project.  After a year of monitoring, a revised geotechnical report was prepared that now considered containment dike performance and the actual settlement rates documented by the pilot study.  The revised report indicated that the marsh creation project had a lot higher chance of supporting an emergent marsh platform than originally thought.  Despite the great news, there was still a lot of work to be done.  The LaBranche Marsh Creation Project had to be designed to the 95% level to compete for construction funding.

Funding Approval and Construction Kick-Off

The NRCS planning and design team kept trudging along with the goal of project construction.  However, and as it should be, competition for funding under CWPPRA is extremely competitive.  Keeping this in mind, NRCS worked hard to design a marsh creation project that would be cost-effective while providing maximum environmental benefits.  Our main objective was to build a marsh platform to a target elevation capable of supporting a healthy, vibrant, tidally-influenced, emergent marsh with a respectable project life.  Also, project features were planned to enhance the marsh creation area for fish and wildlife.

When competing for funding, cost-effectiveness is a major factor in the project selection process.  After considering cost-effectiveness, NRCS proposed combining PO-133 with PO-75 for construction.  Due to the millions of dollars in savings gained by combining the construction of the 2 projects, the idea of a “combined project” was looked upon favorably by the CWPPRA team, and funding was approved for PO-133 in 2021.  With construction funding approved for both projects by CWPPRA, NRCS began final design for one of the largest marsh creation projects ever proposed in Louisiana.

Current Status

About 33,612 linear feet of containment dikes have been constructed around marsh creation cells 1 and 2. Construction on about 21,000 linear feet of containment dikes around cell 3 will be completed in the Fall of 2023. Pumping of dredged fill material from Lake Pontchartrain is scheduled to begin in April of 2024.

Goals and Projections

The LaBranche Marsh Creation Project (PO-75), proposing to create approximately 1500 acres of marsh, is under construction and is expected to be completed by mid-year 2025 (Figure 2).  PO-75 is located adjacent to PO-17 (“The original CWPPRA project”).  Once PO-75 is complete, the 2 project areas together will form almost 2000 acres of contiguous emergent marsh providing benefits to the Lake Pontchartrain Estuary and the Lake Pontchartrain Basin.  That’s roughly 10% of the LaBranche Wetlands.  The extensive tract of contiguous emergent marsh will exponentially increase the estuary functions in the Lake Pontchartrain Estuary and help maintain the overall environmental quality of the Pontchartrain Basin.

How this Project Benefits the Public

Why does it matter that this once thriving marsh ecosystem is disappearing? And, why are we spending so much time, effort, and money to try to rebuild it? The most basic answer is that if we don’t do something, we’ll continue to lose marsh and the effects will continue to compound negatively.

We get several benefits from having a healthy marsh, most of which you may never actually notice. The most obvious and visual benefits are better wildlife habitat with increased diversity and enhanced recreational opportunities in the area. The not-so-noticeable benefits are equally, if not more, important. The marsh serves as a large filter improving water quality for the ecosystem it supports as well as for us. It also acts as a buffer helping protect critical transportation infrastructure (the railroad and I-10) during storms. I-10 is a key hurricane evacuation route for the New Orleans Metropolitan area and reestablishing marsh and improving the wetlands surrounding the area supports strong, reliable routes to safety. And finally, healthy marshes can help slow the effects of flooding during heavy rains lessening the impacts to the surrounding area.

So, the next time you’re heading down I-10 between LaPlace and New Orleans, take the opportunity to admire the work being done to rebuild our marsh.

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