Tidal Inlet Evolution in the Mississippi River Delta Plain

Abstract

A sequence of tidal inlet morphologies ranging from wave- to tide-dominated occurs along the shoreline of the Mississippi River Delta Plain. There is no appreciable variation in the mean tidal range (0.35 m) or mean significant wave height (0.5 m) in this reach of coastal Louisiana. The arrangement of sand bodies in the individual inlets is associated with the tidal prism exchanged between the respective bay and the Gulf of Mexico, and sediment supply. This study presents the argument that temporal changes in tidal prism and sediment supply results in a sequential change of inlet morphology. This inlet evolution is noted during the abandonment phase of individual delta lobes of the Mississippi River. During the first stage of abandonment, represented by headlands flanked by barrier spits, high rates of subsidence cause bays to expand. As bay area increases, tidal prism increases causing wave dominated inlets to evolve tide-dominated morphologies. At the beginning of the second stage of delta lobe abandonment (barrier island arc systems) the sediment supply becomes limited. The spits confining tide-dominated inlets fragment causing the inlet throat to widen; tidal current strength decreases and waves begin to fill the main ebb channel with sands derived from the ebb tidal delta.