Modeling potential benefits of fragmented terrace restoration in Terrebonne Bay, Louisiana: wave attenuation, sediment process, and potential SAV habitat
Abstract
Marsh terraces are being built across the Louisiana coast as an approach to coastal restoration and protection. Terraces are built to reduce coastal edge erosion and increase sediment retention while creating high value aquatic habitat for fish and waterfowl. In order to evaluate the relative effectiveness of terrace designs, a hypothetical model was developed using Delft3D. To consider the terrace elevation changes through the wave and current interaction, a wave model (D-WAVE) was coupled with the hydro and morphodynamic model (D-FLOW-SED-ONLINE). To characterize the model, field sampling of vegetation and physical environmental parameters were conducted in coastal Louisiana. First, five different types of terrace (i.e., Chevron with 100m spacing, Chevron with 200m spacing, Linear, Box, and T-Shape) were evaluated under varied environmental conditions (calm and storm) in terms of the terrace stability and sediment retention. Model runs demonstrated that the box style terrace was the preferred design, chevron and linear designs also were effective for perpendicular wind and wave direction. Using the preferred design, the effects of vegetation, bottom elevation, and sediment type on the terrace stability and sedimentation were evaluated under calm and storm conditions. In addition, Submerged Aquatic Vegetation (SAV) potential habitat was assessed based on water depth and bottom shear stress under the same scenarios. Vegetation presence reduced terrace erosion, but vegetation height had a greater influence than vegetation density in reducing erosion on terraces. Terraces constructed primarily of finer sediment (mud size range; up to 63 mm) terraces had greater stability than sand when vegetation was present. Deeper water depths between terraces increased sediment retention. Overall, the sediment type was the most significant factor for determining terrace stability. Vegetation type was also an important factor to increase sediment retention. SAV potential growth habitat in the current tests was most impacted by water depth rather than bottom shear stress, even for the storm condition. Though this model was based on specific Louisiana marsh sites, it is applicable for terrace restoration anywhere adequate input data is available.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMEP11E2078J
- Keywords:
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- 3020 Littoral processes;
- MARINE GEOLOGY AND GEOPHYSICS;
- 4315 Monitoring;
- forecasting;
- prediction;
- NATURAL HAZARDS;
- 4316 Physical modeling;
- NATURAL HAZARDS;
- 4217 Coastal processes;
- OCEANOGRAPHY: GENERAL