Volume-based reflection characteristics of tsunami-like waves at coastal revetments under overtopping conditions

초록

This study presents a volume-based reflection framework for tsunami-like waves overtopping coastal revetments. The proposed framework addresses the limitations of conventional peak-based metrics for quantifying the volume of water returning seaward. The reflection characteristics were quantified using two-dimensional hydraulic flume experiments for a vertical revetment (VR) and a wave-absorbing revetment (WAR). Incident and reflected free-surface elevation time histories were separated, and reflection coefficients based on wave amplitude, wave height, and reflected water volume were evaluated. The volume-based coefficient was obtained by integrating the reflected water volume, accounting for nonlinear wave celerity. Experimental results show that peak-based reflection coefficients decrease rapidly as overtopping intensifies, whereas the volume-based coefficient remains substantial. This result indicates that a significant portion of the incident water volume still returns seaward despite the reduction in reflected crest elevation. In addition, a mass conservation framework was used to decompose the incident volume into reflected, overtopped, and delayed-return components, showing that the delayed-return component contributes to persistent long-period hydrodynamic responses. These findings suggest that conventional peak-based metrics may underestimate tsunami-induced hydrodynamic persistence under overtopping conditions. In contrast, the proposed volume-based framework provides a robust basis for assessing reflection characteristics at coastal and harbor structures under overtopping conditions.

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