Simulation of tsunami-induced sediment transport and coastal morphology change

Abstract

Throughout history, tsunamis have consistently impacted the United States, affecting both the East and West Coasts. The National Tsunami Hazard Mitigation Program (NTHMP) currently develops maximum potential tsunami inundation maps for the U.S. East Coast (USEC) utilizing a range of tsunami sources. However, these maps do not yet account for the impact of sediment transport and changes in coastal morphology, due to the incomplete understanding and validation of these factors. The USEC features sandy shorelines and is largely shielded by barrier islands protecting inland areas. Previous simulations, which excluded sediment transport and morphological change, indicate that tsunami waves could overtop these barrier islands and sandy coasts, posing a threat to the inundated areas and mainland. Historical tsunamis have demonstrated that such inundation can cause significant erosion and deposition further inland and offshore, driven by sediment dynamics, resulting in altered landforms and damage to harbors and coastal infrastructure. ☐ This research aims to advance understanding of the extent of hazards and sediment transport processes from past tsunamis and enhance predictions for future events by improving an existing sediment transport and morphology model. This model integrates sediment transport processes into the Boussinesq hydrodynamic model, FUNWAVE-TVD. Improvements include optimizing the hindered settling coefficient, refining the settling velocity equation, incorporating bed load transport, and enhancing the interaction between hydrodynamics and sediment transport in flows with high sediment concentrations. This upgraded model has been validated against wave flume experiments that examined hydrodynamics, sediment transport, and morphological changes under varying conditions of wave forms and land slopes. It has also been validated against observations of tsunami-induced morphological changes during the 2011 Tohoku event. The findings demonstrate that the new model effectively replicates observed hydrodynamics and patterns of erosion and deposition across all tested scenarios, thereby improving hazard assessment capabilities of the model under diverse hydrological and bathymetric conditions. Following successful experimental validation, the model was applied to Suffolk County, NY, a low-lying coastal community along the USEC protected by a barrier island. Analysis using four potential tsunami sources revealed that tsunamis can cause significant morphological changes to the barrier island and modify hazard extents. These results underscore the importance of including sediment transport models coupled with hydrodynamic analyses in future tsunami risk assessments.