During the summer of 2005, Hurricane Dennis overwashed the eastern portion of St. George Island, part of the northwest barrier island chain located along the Florida Panhandle. In this paper, LiDAR-based morphological changes of the barrier island are analyzed, along with the short-term post-storm recovery of secondary dunes. Results show that overwash from the storm surge removed nearly the entire foredune complex, and the initial breaching probably occurred where the complex was either low or discontinuous; in these locations, beach widening was less. In contrast, approximately 10 m of beach widening occurred where foredunes were higher and continuous, implying that more sediment was available for seaward transport during storm conditions. The secondary dunes recovered at an average linear rate of 3-4 cm per month in the presence of vegetation, although monthly averages varied from −1.5 to 1.4 m 3 /m and total volume changes varied from −17.9 to 16.4 m 3 /m for the duration of the study. Furthermore, vegetation deterred dune migration, thus favoring dune growth and reducing erosion due to wind. In contrast, the absence of vegetation inhibited dune growth. Insignificant changes in elevation occurred in areas of storm debris or lag deposit. Finally, distributions of topographic gradients and curvature calculated numerically from pre-and post-storm LiDAR data are introduced as a potential tool in determining the relative post-storm recovery of the dune field.
The relationship between lateral erosion of salt marshes and wind waves is studied in Hog Island Bay, Virginia USA, with high-resolution field measurements and aerial photographs. Marsh retreat is compared to wave climate calculated in the bay using the spectral wave-model Simulating Waves Nearshore (SWAN). We confirm the existence of a linear relationship between long-term salt marsh erosion and wave energy, and show that wave power can serve as a good proxy for average salt-marsh erosion rates. At each site, erosion rates are consistent across several temporal scales, ranging from months to decades, and are strongly related to wave power. On the contrary, erosion rates vary in space and weakly depend on the spatial distribution of wave energy. We ascribe this variability to spatial variations in geotechnical, biological, and morphological marsh attributes. Our detailed field measurements indicate that at a small spatial scale (tens of meters), a positive feedback between salt marsh geometry and wave action causes erosion rates to increase with boundary sinuosity. However, at the scale of the entire marsh boundary (hundreds of meters), this relationship is reversed: those sites that are more OPEN ACCESS J. Mar. Sci. Eng. 2015, 3 1042 rapidly eroding have a marsh boundary which is significantly smoother than the marsh boundary of sheltered and slowly eroding marshes.
Tidal channels are ubiquitous in muddy coastlines and play a critical role in the redistribution of sediments, thus dictating the general evolution of intertidal landforms. In muddy coastlines, the morphology of tidal channels and adjacent marshes strongly depends on the supply of fi ne sediments from the shelf and on the resuspension of sediments by wind waves. To investigate the processes that regulate sediment fl uxes in muddy coastlines, we measured tidal velocity and sediment concentration in Little Constance Bayou, a tidal channel in the Rockefeller State Wildlife Refuge, Louisiana, USA. The tidal measurements were integrated with measurements of wave activity in the bay at the mouth of the channel, thus allowing the quantifi cation of feedbacks between waves and sediment fl uxes. Results indicate that the sediment concentration in the channel is directly related to the wave height in the adjacent bay during fl ood and high slack water, whereas the concentration during ebb depends on local channel velocity. Moreover, the sediment fl ux during ebb is of the same order of magnitude as the sediment fl ux during the previous fl ood, indicating that only a small fraction of transported sediments are stored in the marsh during a tidal cycle. Finally, very low tides, characterized by high ebb velocities, export large volumes of sediment to the ocean.
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