Coastal application of unstructured WAVEWATCH III in swell-dominated waters

Spectral wave models are widely applied in wave hindcasting for scientific research and ocean engineering. In this study, the performance of Unstructured WAVEWATCH III (UNWWIII) in coastal shallow waters is evaluated against in-situ measurements and results from unstructured Simulating Waves Nearshore (UNSWAN), with a focus on swell-dominated conditions. A structured multi-grid WAVEWATCH III system is implemented for the Indian Ocean to provide high-quality incident boundary wave spectra for the coastal unstructured models. The ocean-scale model is calibrated and validated using denoised along-track significant wave heights from the European Space Agency’s Sea State Climate Change Initiative (ESA CCI) dataset and in-situ moored buoy observations. Unstructured wave models are then established for the coastal waters of Hambantota, Sri Lanka, using both UNWWIII and UNSWAN. The performance of UNWWIII is comprehensively assessed using bulk wave parameters, energy spectra, and directional spectra against field measurements. Results indicate that UNWWIII yields comparable performance to UNSWAN in reproducing coastal wave conditions. Differences between the explicit and implicit solvers coupled with domain decomposition are also examined. Both numerical schemes agree well with observations. This study provides a practical reference for wave hindcasting at both oceanic and coastal scales.