First-Order Controls of Extreme-Storm Impacts on the Mississippi–Alabama Barrier-Island Chain

Abstract

Predicting the morphological impacts and associated hazards of extreme storms on barrier islands is facilitated by examining historical poststorm images and identifying the predominant alongshore and cross-shore patterns of erosion and deposition for different island segments. Morphological changes on the Mississippi–Alabama barrier-island chain produced by 12 Category 3 and stronger hurricanes since 1852 were analyzed to investigate whether barrier-island responses to extreme storms are controlled primarily by local geomorphic conditions or primarily by storm characteristics. Results of those analyses demonstrate that (1) antecedent topography and geomorphic conditions (island width, land elevations, nearshore bathymetry, subaqueous-boundary conditions) tend to exert greater control on local barrier-island impacts than storm parameters (path, intensity, wind speeds, water levels, shelf duration), and (2) types and alongshore patterns of storm overwash and island breaching are commonly repeated for the same island segments. Even when impact patterns are identical, magnitudes of sequential impacts, such as the inland distance of sediment transport, are unequal and are controlled by storm parameters (water levels, wind speeds) that influence wave heights, overwash-flow depths, and current velocities.