ABSTRACT: Regimes Contributory to Progressive Loss of Alabama Coastal Shoreline and Wetlands

Everett Smith

Coastal survey data from the 1700s to the present indicate progressive loss of Alabama coastal shoreline and wetlands. Alabama coastal shoreline/wetland environments include those of bays, estuaries, Mississippi Sound, lagoons, lakes, fluvial deltas, and Gulf barrier. Areas showing the highest rates of loss include Mississippi Sound north shoreline and islands, Mobile Bay west shoreline, Gulf shoreline of Dauphin Island, and north shoreline of Morgan Peninsula. Other areas showing progressive substantial loss are Mobile Bay east shoreline, Perdido Bay, and Perdido estuary. The relationship between erosional loss and accretionary gain of Gulf barrier shoreline in Baldwin County (from Mobile Point to Alabama Point) is complex, but this shoreline appears to be generally stab e with isolated short segments of erosional as well as accretionary beach. Negative economic results of shoreline/ wetland loss include shoreline property devaluation, costs associated with erosion protection, and loss of wetlands supportive of fishery species reproduction. Accretionary gain of land areas appears to be negligible. Although no new wetlands appear to be developing along Mississippi Sound shoreline exposed to erosional affects of waves and currents, it is postulated that subsidence and drowning of terrane adjacent to Mississippi Sound is resulting in some new upland swamp and bayou areas. The balance between loss and gain of wetlands has not been estimated. General descriptions are given for the unique combinations of factors postulated as contributory to loss of specific s oreline/wetland. Primary factors associated with shoreline loss are wave, current, and tidal parameters, local subsidence, sea-level rise, position and character of natural barriers, position and nature of shoreline protection structures, anthropogenic effects, local bathymetry, shoreline orientation, local sediment budgets, and morphological and physical character of shoreline/wetland.

AAPG Search and Discovery Article #90999©1990 GCAGS and Gulf Coast Section SEPM Meeting, Lafayette, Louisiana, October 17-19, 1990