Validation of SWAN wave directions

In this report the SWAN performance in complex tidal inlet systems regarding wave directions for storm conditions was studied for SWAN runs in stationary mode. In addition, it was investigated what the SWAN accuracy concerning wave directions implies for the hydraulic loads and the required crest height. The performance of the SWAN mean wave direction was studied in a statistical error analysis using the results of existing hindcast studies in the Amelander Zeegat, the Eastern Wadden Sea and the Western Scheldt. Close to the coast there are limited directional measurements available. However, the few observations show that SWAN biases of 10 to 20 degrees in the mean wave direction are likely with a standard deviation of circa 5 degrees. In addition, the directional spreading is underestimated with 10 to 20 degrees and the standard deviation is a few degrees. The agreement between the computed and measured mean wave directions is better in cases where wind-sea predominates than in cases where low-frequency wave penetration is measured.