Abstract
Coastal wetlands are a crucial buffer zone between land and sea but lateral erosion threatens their long-term sustainability. Better understanding of the forces leading to lateral marsh retreat will benefit the assessment of management options applied to mitigate the erosion. Terrestrial Laser Scanning (TLS), Light Detection and Ranging (lidar), and associated technologies are increasingly being used to assess this erosion. The central objective of this study was to identify a methodology for measuring marsh edge erosion with a TLS and correlate that erosion with exposed roots and incident wave energy. We quantified edge erosion across multiple temporal and spatial scales using a TLS, showing greater than one meter of lateral erosion over a 318-day period. We then evaluated the relationships between the erosion and incident wave energy along with erosion and vegetation roots. Wave height and erosion was strongly related (r2 = 0.99), while vegetation roots did not show an apparent effect. We discuss the challenges that arise from using TLS equipment, TLS data sets, and the use of voxels to measure marsh edge erosion.
Highlights
Coastal zones are in a constant state of physical and geological flux caused by tidal activity, sea level rise, and high energy events such as strong storms
Using the hindcast wind wave model that was constructed, the fit was strong between C2C erosion metric during a given interval with the cumulative significant wave height during that same interval (r2 = 0.95) and the M3C2 metric was still more strongly correlated at r2 = 0.99
While the relationships were strong, we note that the sample size for each consisted of four data points, as limited by the number of Terrestrial Laser Scanning (TLS) sample intervals
Summary
Coastal zones are in a constant state of physical and geological flux caused by tidal activity, sea level rise, and high energy events such as strong storms. The images gathered by both methods are usually nadir-oriented, only allowing for a two-dimensional assessment of marsh retreat with little information about the vertical edge. Methods such as structure from motion (SfM) can give a three-dimensional product useful for surface topographic modeling. This method is not applicable to most salt marsh edge erosion studies due to soil and plants overhanging the scarped marsh edge. This overhang creates a shadow in the imagery. To minimize the shadowing an angle close to 90 degrees from the scarped edge is desirable for data acquisition
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