Numerical modeling and observations of infragravity wave propagation and amplification within a small, confined harbor

Abstract

Infragravity (IG) waves are long-period oscillations capable of propagating into and resonating within harbors, and pose significant risks to maritime operations. High-resolution water level observations suggest the dominant IG wave energy source within in a small harbor originate offshore, propagating as free waves that undergo amplification due to the harbor’s geometric configuration, resulting in significant harbor seiching. Strong correlations are observed between offshore wave parameters and IG wave energy, with significant wave height and average wave period being the primary drivers. Additionally, directional wave spreading plays a critical role in the generation and propagation of IG waves. A numerical modeling framework, using SWAN to resolve the nearshore wave climatology and FUNWAVE-TVD to investigate harbor resonance, successfully models IG wave amplification events and enables the identification of the eigenmodes and nodal patterns within the harbor. However, the coupled modeling methodology under-predicts the propagation of short-period wind waves into the harbor which nominally contribute to wave agitation. Results highlight the crucial influence of wave directionality, directional spread, and spectral shape on IG wave amplification in confined coastal environments. These findings enhance our understanding of IG wave dynamics and have important implications for harbor design, coastal resilience, and maritime safety.