A Geomorphic Process-Response Model for Chenier-Plain Evolution in Southwestern Louisiana, USA

Coastal morphodynamics are evaluated to develop a more-advanced geomorphic model for chenier-plain evolution in southwestern Louisiana. Most ridges on the chenier plain represent open-Gulf paleoshorelines. Past movement trends of individual shorelines allow ridges to be further classified as transgressive, regressive, or laterally accreted. As such, a geomorphic hierarchy of landforms is refined relative to dominant coastal process. To understand long-term evolution of the chenier plain, modern tidal-inlet processes operating at Sabine Pass, Calcasieu Pass, and the Mermentau River mouth are examined relative to the inlet-stability ratio; historical shoreline-change data are used to document trends in. shoreline behavior; and air-photo interpretation and topographic profiles are used to address form/process relationships of primary landforms. These datasets and others indicate that the geologic evolution of the chenier plain is more complicated than just channel avulsions of the Mississippi River and downstream delta switching. A six-stage geomorphic process-response model is presented that synthesizes chenier-plain evolution primarily as a function of: 1) the balance between sediment supply and energy dissipation, 2) local sediment reworking and lateral transport, and 3) tidal-entrance dynamics.