Modeling Long-Term and Regional Shoreline Evolution around Coastal Inlet

Prediction of long-term and regional-scale shoreline evolution is essential for planning and management of coastal erosion protection measures such as grey infrastructure and natural and nature-based features (e.g. beach nourishment). Modeling shoreline changes in barrier islands needs to take into account the sediment exchange between inlet morphological elements and adjacent beaches. Those morphological elements include an ebb shoal, flood shoal, bypass bars, and attachment bars. Although multi-dimensional coastal processes models are able to produce high-resolution simulation results of spatiotemporal variations of sediment transport and morphological changes over the shoals and bars of an inlet, the existing multi-dimensional models are still incapable of predicting long-term (decadal) and regional variations of the morphological elements and shoreline. Therefore, a shoreline evolution model (i.e., oneline" model) together with an empirical model for predicting volumetric evolution of the inlet morphology becomes a practical simulation approach to predict long-term and regional shoreline evolution around coastal inlets. The USACE shoreline evolution model, GENCADE, including the Inlet Reservoir Model was applied in this study to simulate decadal shoreline changes around two inlets on the east coast of the United States. The simulations consider various driving factors of shoreline change such as waves, longshore and cross-shore sediment transport, shoreline retreat due to sea level rising, coastal structures (jetties, groins, seawall, etc.), and erosion protection measures (sand bypassing, beach nourishment, and beach fills). Model validations were performed by evaluating statistic errors of simulated shoreline positions, by comparing with historical shoreline positions. Efficacy of sediment exchange between inlet and shores was quantified by the volumetric changes of shoals and bars estimated by the IRM model. Long-term effects of coastal erosion protections such as sand bypassing across the inlet were evaluated by the shoreline model results. Numerical simulation of shoreline evolution and inlet morphological evolution provides better understanding of the morphodynamics of inlet shoals and adjacent shorelines, and provides a quantitative assessment of sediment transport along barrier islands and the impacts of erosion protection practices.