Modelling fetch-limited wave growth from an irregular shoreline

The wave model WAM was used to study the effect of the grid resolution and the description of an irregular shoreline on modelling of fetch-limited wave growth. Three different methods to compile a grid for a wave model in the case of an irregular shoreline are discussed. Several combinations of shoreline description, grid resolution, and wind field were used to model the effect of the irregularities of the shoreline on fetch-limited wave growth. The modelling confirmed the usual assumption that these effects will rapidly vanish as the distance from the shore increases. However, close to the shoreline the differences between the modelled values of significant wave height were relatively large. The modelled spectral wave parameters were compared against wave measurements made in the Bothnian Sea in 1976. None of the combinations was able accurately to predict the measured wave growth. Close to the shoreline the modelled wave energy and peak period grew too fast, and further offshore the modelled wave energy was underestimated. Close to the shoreline the most accurate results were obtained when a high-resolution grid of 0.25 nmi was used together with a re-analysed wind field from the atmospheric model HIRLAM. The effect of grid resolution on the growth rate of the wave energy at short fetch was relatively large.

► We used wave model WAM to study fetch-limited wave growth from irregular shoreline. ► We studied several combinations of shoreline description, resolution and wind forcing. ► None of the combinations was able accurately to predict the measured wave growth. ► The effect of the shoreline description was significant up to 40 km from the shore. ► Grid resolution had notable effect on the growth rate of wave energy.