Simulations of Dissipative, Shore-Oblique Infragravity Waves

Abstract

A model of forced, dissipative shore-oblique shallow water waves predicts net cross-shore infragravity wave propagation, in qualitative agreement with field observations. Forcing applied near the shore generates edge waves, whose energy is mostly trapped shoreward of the edge wave turning point. Forcing applied sufficiently far seaward of the turning point generates only evanescent waves, whose energy decays almost exponentially with distance from regions of forcing. Weakly dissipative edge waves are nearly cross-shore standing, whereas strongly dissipative edge waves propagate obliquely across-shore. Groups of directionally spread incident waves can nonlinearly force evanescent bound waves, which propagate shoreward, lowering the sea level under large incident waves. Unlike the bound waves described by previous researchers, evanescent bound waves are not released when incident waves break and do not radiate far from the breakpoint. Regions of evanescent waves between the shoreface and shore-parallel sandbars are barriers to energy transport, which can decouple bar- and shore-trapped waves even when dissipation is weak.