Island Edge Morphodynamics along a Chronosequence in a Prograding Deltaic Floodplain Wetland

Much of the previous research on coastal deltaic land building has focused on the planform delta dimensions; whereas this research focuses on shifts in vertical elevation and deltaic island edge cross-sectional morphology in relation to a proposed conceptual model of deltaic island edge morphological development. This study was conducted using data collected from the Wax Lake Delta in the northern Gulf of Mexico. Island edge cross-sectional elevation profiles were extracted from a 2012 LIDAR elevation survey. Four morphometric variables (levee width, interior slope, mean elevation range, and total elevation range) were selected to describe the shape of each of these profiles, and each profile was also assigned to an age class, which was determined based on mapping of historic deltaic island extent from aerial imagery. Multivariate analysis of variance was used to test the effect of age class and distance from the upstream end of the island on these four morphometric variables. Results indicated that both age and the distance within age were statistically significant predictors of island edge cross-sectional morphology. Field-surveyed elevation transects also followed the predicted pattern of morphologic change and illustrated that the shifts in morphology can occur very rapidly within this system-over a matter of a few months-as the result of a single large river flood. High soil percent organic matter was also found to correlate to high elevation in field-surveyed transects, indicating that biological processes such as organic matter production and accretion may also play an important role in morphological development of deltaic floodplain wetlands.