On the use of instrumental data for infragravity wave simulations.

Infragravity (IG) waves are surface ocean waves with periods ranging from 25 s to 300 s. They typically have low amplitudes and wavelengths an order of magnitude longer than wind-generated waves. IG waves can penetrate ports and harbours, and their reflection off port's internal walls and structures can generate resonance when the port's basin and IG wave lengths are similar. The amplification of the IG wave energy by resonance can cause surge motion on moored vessels, which can break mooring lines and threaten personnel safety. Most studies considering IG wave effects in harbours use white noise (synthetic) boundary forcings in simulations to identify the wave periods that can cause resonance within a port layout, or in run spectral simulations based on the statistics of the local wave climate. Although synthetic boundaries can effectively provide such resonance periods for ports, it is not possible to predict whether these long-period oscillations or resonance will effectively occur under the natural wave climate. On the other hand, simulations based on the local wave climate use bulk wave parameters, which are not capable to represent the multiple wave systems (i.e., seas and swells) that can be present on the wave spectrum. In this paper, we use concurrent offshore and in-basin wave measurements to study IG waves processes in Eastland Port, Gisborne (NZ). We selected a range of IG wave events recorded by an IG wave radar within the port basin and used the simultaneous spectral offshore wave condition as boundary forcings for SWASH simulations. Results show the different spatial distributions of IG wave heights that can occur within the port basin, and identifies the differences in wave spectra for the cases modelled. The study highlights the importance of using realistic wave conditions for IG wave investigations. [ABSTRACT FROM AUTHOR]