Simulation of Long-term Shoreline Evolution Driven by Longshore and Cross-shore Transport

Abstract:

Long-term simulation of shoreline evolution along the Duck coast in NC was performed to validate the USACE shoreline change model which integrates longshore and cross-shore sediment transport. The new capability for cross-shore transport was developed to calculate subaqueous cross-shore sediment transport driven by waves, currents, and gravity. To correctly estimate asymmetrical near-bed orbital velocity which is a key parameter to predict cross-shore transport rate in nearshore zone, a nonlinear wave shape model was adopted. Meanwhile, undertow current was estimated by an empirical parametric model, which is important to predict beach erosion by offshore transport during storms.

Calibration of model parameters and validation were performed by simulating shoreline changes for a 5-km-long coastline in Duck, NC over a 14-year period from 2000 to 2013. Careful evaluation of model skill performance shows that the simulation with cross-shore transport significantly improves the prediction accuracy of the long-term shoreline change. Successful model validation demonstrates that including longshore and cross-shore transport enables this shoreline model to reproduce the seasonal and annual variations of shoreline positions in the coast (Figures 1 and 2). Sensitivity analysis of shoreline position with respect to a permeable pier located within the domain reveals that sediment bypassing varies with wave conditions and longshore sediment transport direction. This cross-shore transport capability enhances long-term simulation applicability of this model for planning and management of coastal protection practices.