Storm-induced sediment transport at a small tidal inlet

Evaluating sediment transport through tidal inlets is critical for understanding shoreline and backbarrier evolution and for maintaining tidal exchange and vessel navigation. Storm-driven sedimentation is important in determining long-term backbarrier sediment budgets and ecosystem evolution, particularly with the forecasted increase in frequency and magnitude of storms under a regime of climate change. The primary objective of this study is to investigate sediment dynamics during storm and normal tidal conditions and predict net sediment deposition patterns at Allens Pond Inlet, a small inlet in southern Massachusetts. Small inlets (width <100 m) represent an understudied tidal system even though small inlets commonly out-number large inlets along coasts. A hydro- and morpho-dynamic model, Delft3D, was employed to simulate tides, storm-generated currents, and sediment transport. An Acoustic Doppler Current Profiler and water level logger were deployed for model input and validation. Sediment samples from the study area reveal a gradient of fining grain size from the inlet entrance to the backbarrier channels, indicating landward sediment transport. Hydraulic measurements demonstrate a correlation between tidal range and current velocities and confirm that spring tidal ranges produce dominant flood-dominance of the system. Moreover, our modeling results show that storm events significantly enhance sediment influx due to higher order current velocities at the inlet and in backbarrier tidal channels. Our findings explain the formation and landward migration of flood-oriented bedforms, point bars, and tidal deltas suggesting that backbarrier of small inlets are sediment sinks.

https://doi.org/10.1016/j.coas...