Shoreline stabilization, living shoreline, wave attenuation, shoreline erosion, wave tank, soft stabilization
Coastal counties make up only 17% of the land area in the continental United States, yet 53% of the nation’s population resides in these locations. With sea level rise, erosion, and human disturbances all effecting coastal areas, researchers are working to find strategies to protect and stabilize current and future shorelines. In order to maintain shoreline stability while maintaining intertidal habitat, multipurpose living shorelines have been developed to mimic natural shoreline assemblages while preventing erosion. This project determined the effectiveness of a living shoreline stabilization containing Crassostrea virginica (eastern oyster) and Spartina alterniflora (smooth cordgrass) in the field and through controlled wave tank experiments. First, fringing oyster reefs constructed of stabilized oyster shell and smooth cordgrass plugs were placed along three eroding shoreline areas (shell middens) within Canaveral National Seashore (CANA), New Smyrna Beach, FL. For each shell midden site, four treatments (bare shoreline control, oyster shell only, S. alterniflora only, and oyster shell + S. alterniflora) were tested in replicate 3.5 x 3.5 meter areas in the lower and middle intertidal zones. Each treatment was replicated five times at each site; erosion stakes within each replicate allowed measurement of changes in sedimentation. After one year in the field, the living shoreline treatments that contained oyster shells (oyster shell only and oyster shell + S. alterniflora) vertically accreted on average 4.9 cm of sediment at two of the sites, and an average of 2.9 cm of sediment at the third, while the controls lost an average of 0.5 cm of sediment. S. alterniflora did not significantly contribute to the accretion at any site due to seagrass wrack covering and killing plants within one month of deployment. Next, the reduction in wave energy caused by these living shoreline stabilization techniques relative to bare sediment (control) was quantified. The energy reduction immediately after deployment, and the change in energy reduction when S. alterniflora had been allowed to grow for one year, and the stabilized shell was able to recruit oysters for one year was tested. Laboratory experiments were conducted in a nine-meter long wave tank using capacitance wave gauges to ultimately measure changes in wave height before and after treatments. Wave energy was calculated for each newly deployed and one-year old shoreline stabilization treatment. Boat wake characteristics from CANA shorelines were measured in the field and used as inputs to drive the physical modeling. Likewise, in the wave tank, the topography adjacent to the shell midden sites was measured and replicated. Oyster shell plus S. alterniflora attenuated significantly more wave energy than either the shells or plants alone. Also, one-year old treatments attenuated significantly more energy than the newly deployed treatments. The combination of one-year old S. alterniflora plus live oysters reduced 67% of the wave energy. With the information gathered from both the field and wave experiments, CANA chose to utilize living shorelines to stabilize three shell middens within the park. Oyster shell, marsh grass and two types of mangroves (Rhizophora mangle, Avicennia germinans) were deployed on the intertidal zones of the eroding middens. Significant accretion occurred at all middens. Two sites (Castle Windy and Garver Island) vertically accreted an average 2.3 cm of sediment after nine months, and six months respectively, and the other site (Hong Kong) received on average 1.6 cm of sediment after six months. All control areas (no stabilization) experienced sediment loss, with erosion up to 5.01 cm at Hong Kong. Plant survival was low ( < 20%) at Castle Windy and Garver Island, while Hong Kong had moderate survival (48-65%). Of the surviving marsh iv grass and mangroves on the three sites, almost all ( > 85%) had documented growth in the form of increased height or the production on new shoots. Landowners facing shoreline erosion issues, including park managers at CANA, can use this information in the future to create effective shoreline stabilization protocols. Even though the techniques will vary from location to location, the overall goal of wave attenuation while maintaining shoreline habitat remains. As the research associated with the effectiveness of living shorelines increases, we hope to see more landowners and land managers utilize this form of soft stabilization to armor shorelines.
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Walters, Linda J.
Master of Science (M.S.)
College of Sciences
Length of Campus-only Access
Masters Thesis (Open Access)
Dissertations, Academic -- Sciences, Sciences -- Dissertations, Academic
Manis, Jennifer, "Assessing The Effectiveness Of Living Shoreline Restoration And Quantifying Wave Attenuation In Mosquito Lagoon, Florida" (2013). Electronic Theses and Dissertations. 2814.