Infragravity oscillations in a coupled-basin marina under typhoon conditions: physical model experiments and numerical modeling

Abstract

Harbor tranquility in marinas can be significantly affected by long-period infragravity oscillations during energetic events, yet existing design guidelines still rely primarily on short-period swell–sea wave criteria. This study investigates infragravity oscillations in a coupled-basin marina at Badouzi Harbor in northern Taiwan, using high-resolution physical model experiments and a non-hydrostatic XBeach model. The XBeach model reproduced significant wave heights in both the swell–sea and infragravity bands reasonably well. The results indicate that swell–sea waves in the inner basin generally satisfy the conventional tranquility criterion of 0.5 m under typhoon conditions, whereas infragravity waves exceed this threshold in both the inner and outer basins. Resonance analysis further reveals that longer infragravity oscillations (100–250 s) dominate the inner basin, accounting for more than 70% of the total infragravity energy and exhibiting Helmholtz-mode behavior that can generate strong oscillatory currents at the basin connection. In contrast, the outer basin retains a broader infragravity band expected to influence the motions of moored yachts. These findings demonstrate that harbor layouts optimized for short-wave sheltering may remain vulnerable to infragravity-induced resonance and associated currents in marina design and operational management.