The Biloxi Marsh of the eastern Mississippi River delta plain is exposed to meteorological forces ranging from large-scale, mid-latitude cyclones to smaller scale storms and squalls. Each time that these marsh platforms are exposed to a storm event, the potential exists for either deposition or erosion to take place. This study examines the connection between wind speeds, stratigraphic composition, marsh edge morphology, and marsh edge erosion at 4 sites in the Biloxi Marsh. As much as 2.17 m of erosion were measured during the 9-month study with a maximum, averaged erosion rate of 0.03 m day-1. Shell berm transgression was also documented as the result of winds from a low-pressure system near the site that resulted large waves. Shell berm movement occurred as a result of high wind speeds on shore but there was no connection between wind speeds and erosion for the duration of this study across all sites.

Extensive shell ridges frame the edges of marsh platforms in parts of the Biloxi Marsh of southeast Louisiana. The exact sources of the shells in these accumulations have not been clearly identified but the most likely source is a combination of shells from modern offshore and shells excavated from buried St. Bernard delta deposits. Larger or fetch-protected ridges remain stable through time, whereas ridges facing open water are more mobile, moving as much as 38 m inland from July 2017 to January 2018. Behind stable ridges, marsh platform biomass is relatively unaffected. When ridges are mobile, vegetation is smothered, leaving an exposed platform that lacks aboveground vegetation to dampen wave energy and fragments into “blocks” along its terraced edge, which in turn are deposited onshore. In the future, marshes will likely erode fastest in areas where shell ridges are mobile and remain resistant where shell ridges are stable.

This study examines wind generated waves during winter storms, their transformation/attenuation near the marsh edge, and the resulting saltmarsh edge erosion. A simple numerical model for wave generation, transmission and marsh edge erosion was developed and validated against observations from Lake Borgne, Louisiana. Results suggest that meteorological conditions modify the local water depth via wind or wave setup and atmospheric pressure, thus exerting a first order control on the location of wave attack, which in turn determines the type of wave forces (shear vs. impact) that dominate the erosion process. Scarp failure follows, at a location determined by water level, creating multiple erosive scarps and terraces. High measured erosion, likely due to marsh edge destabilization followed by subsequent frontal passage forces differential marsh erosion, exposing underlying substrate to further erosion. A conceptual model for marsh edge retreat is developed using these observations and supported further by model predictions.