Mesoscale sediment transport at southeastern US tidal inlets: Conceptual model applicable to mixed energy settings

Prediction of shoreline change around inlets at meso-time scales (years to decades) is the next logical step following verification of microscale mode ls. If mesoscale simulations are a goal, a basic question is how microscale models (that simulate processes at hours to weeks) can be scaled up in tim e or whether macroscale geomorphic models (that qualitatively describe chan ges at decades to centuries) can become more quantitative. The authors prop ose an approach that begins with consideration of tidal inlet morphology an d sediment circulation around ebb-tidal deltas. Inlets are the focus becaus e in some barrier island settings such as the southeast U.S. coast, it appe ars a majority of coastal erosion problems at meso-time scales can be trace d to changes in adjacent inlets. Inlet morphology and geomorphic models, ty pical of mixed-energy coastal plain shorelines, are reviewed to illustrate certain common sediment transport patterns. A simplified conceptual model o f inlets at meso-time scale is proposed from which the problem of sediment transport may be spatially partitioned. Four primary inlet domains are cons idered: (A) main ebb channel where tidally generated ebb currents control s ediment discharge, (B) ebb-tidal delta with a broad swash platform that is ultimately in balance between ebb-directed flows and wave- and tide-generat ed shoreward transport, (C) shoal-bypassing zones at the margins of the ebb -tidal delta where sediment shifts unidirectionally from the delta to the s horeline under wave-generated transport, and (D) recurved spits adjacent to the inlet which receive shoal-bypass sediments. Excess sand accumulating i n Domain D becomes subject to longshore advection toward and away from the inlet. A portion nourishes the adjacent beach and the remainder recycles ba ck to the inlet channel (Domain A), completing the inlet transport loop.