Cross-Shore Sediment Transport for Modeling Long-Term Shoreline Evolution

A process-based parametric closure model for estimating cross-shore sediment transport (CST) rate has been developed for simulating long-term shoreline evolution. The formulations of this closure model include calculations of various subaqueous cross-shore transport components induced by waves, currents, and gravity. To better calculate asymmetrical near-bed orbital velocity that is a key to predict the cross-shore transport rate in the nearshore zone, a nonlinear wave-shape model is adopted. By formulating wave nonlinearity to cross-shore transport, this closure model can predict the net on- and offshore transport rates in response to shoreline accretion and erosion driven by waves and currents during low- and high-energetic conditions. This new capability for cross-shore shoreline change has been implemented into a one-line model, primarily driven by longshore sediment transport (LST). Calibration of model parameters and model validation were performed by simulating shoreline changes for a 5 km section of coastline in Duck, North Carolina, over a 14-year period from 2000 to 2013. The simulation results reproduced seasonal shoreline recoveries during low-energetic fair weather and also captured rapid retreats during storms. This shoreline model with inclusion of LST and CST has significantly improved the prediction accuracy of long-term shoreline changes at the study site. Impact analysis of a pier located within the domain reveals that this shoreline model with CST can better simulate sediment bypassing through the structure that depends on multiple local variables such as shoreline positions, updrift longshore transport, waves, and water levels. Therefore, this new shoreline model will facilitate long-term management of sediments and shoreline erosion and impact assessment of coastal structures.

Automated summary

A process-based parametric closure model has been developed for estimating cross-shore sediment transport rate to simulate long-term shoreline evolution. The model includes calculations of various subaqueous transport components and nonlinear wave effects to predict on- and offshore transport rates. Calibration and validation show improved accuracy in predicting shoreline changes, especially during different energy conditions, and the model's inclusion of CST has enhanced the simulation of sediment bypassing through coastal structures.