Optical shoreline tracking for continuous total water level (TWL) monitoring has conventionally been limited by environmental noise that contaminates the target signal. This study addresses this limitation by introducing a Segment Anything Model 2 (SAM2) approach to achieve reliable, long-term shoreline tracking in a complex beach environment. Specifically, the SAM2 approach based on static timestack images (SAM2_T) captures coherent spatiotemporal structures, providing better resistance against common field disturbances compared to sequential video-based tracking (SAM2_V) that relies on the frame-to-frame memory mechanism. This workflow eliminates site-specific parameter tuning and offers high computational efficiency, enabling a highly stable extraction of long-term TWL. By linking this robust dataset with offshore hydrodynamic forcing, the regression analysis identifies the effects of beach morphology changes, enabling further investigation of long-term TWL variability. This comprehensive framework provides a practical, automated solution for long-term coastal monitoring and beach morphodynamics analysis.
Resonant wave interaction is responsible for various marine and coastal phenomena. Of particular importance are mechanisms accounting for mixing of bottom turbid layer at intermediate and shallow water depths. Recent field data indicates growth of harmonic interfacial modes at the interface between turbid layer and clear water by a wave train on the free surface. In this paper, we propose a particular surface-interfacial resonant wave interaction as the responsible mechanism and study it theoretically and experimentally. We show that four oblique harmonic interfacial waves forming a quasi-standing wave in a wave flume may start growing from background noise level through a cubic resonant wave interaction with a surface wave. The competing effects of viscous decaying, surface wave triggering, and nonlinear modulation eventually lead to a stabilized interfacial wave motion. A third-order resonant interaction analysis shows that the interfacial waves exhibit greater growth potential when their propagation directions deviate from that of the surface wave. A set of carefully conducted experiments is used to support the theoretical predictions. The experimental observations also indicate that there exists a frequency range for which harmonic interfacial waves grow while other forms of interfacial instability are absent.
This study presents laboratory experiments in which underwater landslide tsunamis are induced on gentle slopes using stratified sand and silt layers to investigate landslide tsunami generation and wave characteristics. A novel apparatus was developed to initiate slope failure by applying pore-water pressure from the rear side of the slope, enabling the formation of a water film and controlled destabilization of the sediment structure. Maximum water level changes were found to be sensitive to slope angles, initial water depth, and sliding-layer thickness. Tsunami generation was primarily attributed to the landslide body, whereas the subsequent turbidity current had a negligible influence on wave formation. High-resolution 4K camera analysis enabled quantification of landslide kinematics, revealing travel distance and speed trends. These results showed that the initial wave amplitude prediction model substantially overestimated the measured amplitudes, suggesting limitations of idealized models under deformable stratified sedimentary conditions. Furthermore, the influence of the silt layer was examined using permeability estimates. The contrast in permeability between the sand and silt layers implied that the silt layer impeded upward seepage and contributed to localized water accumulation. These findings provide new insight into submarine landslide dynamics and tsunami generation, with implications fornumerical modeling and hazard assessment.
