An Overview of the Fibrous Mats Shoreline Protection Project

Project Name: Fibrous Matting Materials for Shoreline Protection on Barrier Islands and Coastal Marshes in Louisiana.

Regional Strategy: To arrest wave-induced erosion and create submersed aquatic vegetation habitat for shoreline protection in coastal marshes for Louisiana.

Location: Timbalier and Terrebonne Bay barrier islands and interior marshes.

Problem Statement

Coastal environments flanking Louisiana’s interior bays and lakes are experiencing wave-induced erosion in excess of 15 ft. (5 m) per year. The longer-term prognosis is that among other factors, as these environments increase in size, an accompanying increase in fetch length will permit larger waves and acceleration in erosion rates. Preliminary research has shown that in addition to providing critical habitat, submersed aquatic vegetation (SAV) functions to significantly reduce wave energy in the near shore, increases sedimentation, and stabilizes sediments in eroding marsh and low-energy, sandy environments. These functions suggest that establishment of viable and self- sustaining populations of SAV in areas prone to wave-induced erosion, would reduce and possibly reverse the rate of erosion allowing for the creation of new marsh/sandy beach. Preliminary tests in a wave tank and in the field suggest that a new method of SAV restoration that employs the use of fibrous mats, may serve the dual purpose of stabilizing sediments of marsh and back barrier shorelines in Timbalier and Terrebonne Bay, currently eroding at rates in excess of 5m (15 ft.) per year. This project will test a new SAV planting method that may sufficiently reestablish viable SAV communities despite difficult environmental conditions, and evaluate its impact on wave hydrodynamics and possible marsh and sand beach restoration.

Goals

The ultimate goal of this project is to find techniques capable of rapidly arresting coastal marsh erosion and low-energy sand environments in Louisiana, and create a stable environment conducive to land gain through accretionary processes. The more specific goals of this project are:

1. Establish self-sustaining populations of submersed aquatic vegetation.

2. Reduce the rate of loss of back barrier sandy and interior marsh islands, currently experiencing rapid rates of erosion.

3. Test the feasibility of this method as an alternative to SAV restoration, as an effective means of erosion control, and its cost effectiveness as a restoration and erosion techniques.

Objectives

The objectives of this project are:

1. To establish 250 m² (2,700 ft²) of SAV at four sites including back barrier marsh, back barrier sandy, interior marsh island, and small interior bay.

2. Monitor the effects of the established sites on wave energy dissipation and subsequent effects on sedimentation and erosion.

3. Create new shallow water habitat for fish and wildlife resources.

Proposed Solution

This project would create SAV populations in 4 areas of Terrebonne Bay including two on the backside of barrier islands (marsh and sandy beach), and two interior (north bay) sites. In addition to creating habitat, the successful development of SAV populations would serve to perform shoreline stabilization and enhancement by reducing erosion. The concept centers on the fact that when wave speed and energy is slowed to an optimum threshold level, sediments being transported will fall out of suspension and be deposited in the near shore environment. Additional sediment accumulation in the zone were wave-induced turbulence is typically at a maximum, will result in protecting and enhancing SAV growth and reduced wave erosion potential along the adjacent shoreline. The SAV mats will be grown out in a greenhouse environment for pre-establishment, allowing the roots adequate time to firmly imbed into the fibers, and then transported to the restoration sites at the beginning of the growing season (spring to early summer). Each mat will be firmly anchored to the soil enough to withstand periodic storm events. Growth of the vegetation will be monitored seasonally and water quality parameters that affect SAV growth (e.g. temperature, light, salinity, nutrients) will be monitored monthly. Additional analyses may be done following large storm events. Accurate measurements of sedimentation will be accomplished using an advanced SET array and hydrodynamic conditions will be measured on an hourly basis for the entire duration of the project. Hydrodynamic measurements will be made available on the World Wide Web so that scientists can monitor and access the field site after storm events and rapidly quantify response.

Compatibility with Coast 2050

1. Which project components ensure sustainability through vertical accretion of wetland soil?

Since submersed aquatic vegetation naturally functions to promote shoreline stabilization through sedimentation and wave energy reduction, successful reestablishment of these habitats will serve the dual purpose of increasing productivity of fisheries in coastal bays as well as reduce coastal erosion.

2. Which project components ensure linkages with other parts of the coastal ecosystem?

By reestablishing submersed aquatic vegetation along rapidly eroding coastal environments, the integrity of the shoreline will be enhanced by reduced erosion whereby promoting development of emergent marsh vegetation.

3. How does the project contribute to maintaining biodiversity within the basin?

Successful reestablishment of submersed aquatic vegetation communities is in itself an ecosystem enhancement that increases biodiversity multifold. A simple analogy would be a comparison between a forest and an adjacent clear-cut area. SAV populations provide an infrastructure for the development of numerous organisms including benthic invertebrate, crustaceans, and fishes that would otherwise not inhabit bare sediment. By stabilizing shorelines, SAV helps to maintain emergent marsh habitat as well.

4. To what degree does the project sustain the essential functions and values of a natural ecosystem?

One of the strongest reasons for trying this type of methodology is indeed to promote the sustainability of the essential functions and values of a natural ecosystem. Alternative and presently conventional methods for managing erosion of low-energy back barrier shorelines and marshes generally consists of man-made structures that, while function to varying degrees to stabilize shorelines, have very little ecosystem value. The very idea of reestablishing SAV is to rebuild an intact functional ecosystem that has highest value in terms of habitat development and biodiversity.

5. What are the non-wetland benefits of the project?

Coastal wetlands, in general, function to provide protection to the inland communities by reducing the impact of storms as well as provide an economic base through use of natural resources such as waterfowl and fisheries. Since this project involves the creation and preservation of wetland resources it serves to promote these functions.

Project Benefits

We propose the following benefits:

1. Creation of submersed aquatic vegetation communities and wildlife habitat

2. Reduction of marsh loss by increasing sedimentation and shoreline stabilization.

3. Development of a restoration methodology that has multiple benefits including creation of fishery and wildlife habitats, promotes sedimentation and shoreline stabilization, and is cost-effective.

Member of Subcommittee Preparing Fact Sheet

The project team will include the following senior researchers:

Dr. Gregory Stone, Hydrodynamics and Physical Processes-Coastal Studies Institute, LSU.

Dr. Tommy Michot, SAV ecology-USGS, National Wetlands Research Center.

Mr. Ron Boustany, SAV ecology-USGS, National Wetlands Research Center.