Modelling and monitoring waves in the nearshore region

The nearshore region provides the link between the land and the ocean. Waves play a crucial part in many nearshore processes including sediment transport, coastal erosion, dispersion of pollutants, rip currents, and many more. It is also the region where most people interact with the ocean. Nevertheless, the nearshore is not well presented in operational wave forecasts.

Here we test the merit of resolving the nearshore region in a regional WAVEWATCH III ® setup. We test this for two contrasting wave climates: the swell-dominated west coast of British Columbia with tidal ranges up to 4m, and the fetch-limited, non-tidal western Baltic Sea with storm surges reaching +-1.5m. Both models are on unstructured grids, and we test the feasibility of zoomed-in regions of very high grid resolution. The effect of currents and water level are evaluated as additional forcing fields.

The models are validated against in-situ wave buoy observations including an array that tracks the wave evolution along two 2km shoaling paths. Gradual wave height reductions of >25% per km are observed, but little change in the spectral shape or directional characteristics.

 These observations are challenging to replicate in the model. We find that the inclusion of currents and water level yield the strongest improvement on significant wave heights and directional spreading, whereas increased grid resolution is beneficial for resolving small-scale bathymetric features.