How do simple wave models perform compared with sophisticated models and measurements in the Gulf of Finland?

Wave parameters form the base for the design of coastal structures. For this purpose, commonly modelled wave properties are employed. This approach is usually adequate in open ocean conditions where spatial variations in wave properties are normally quite limited. The situation is different in nearshore areas of complicated shapes, where wave properties can be highly variable. In such instances, long and sufficiently detailed wave measurements for model validation are usually unavailable. The use of default settings of wave models means that possible errors remain unknown, and employing data with substantial uncertainties could lead to overdimensioned structures or structural failures. We address the magnitude of possible errors in such conditions by comparing the output of simple wave models (such as the fetch-based SPM model or the SWAN model forced with one-point homogenous wind) and the sophisticated multi-nested SWAN wave model forced with ERA5 winds with recent wave measurements in various nearshore locations in the eastern Baltic Sea. We use records of different length spanning over more than ten years. While in some locations simple models or models forced with homogenous wind yield acceptable results, in most areas more sophisticated models are needed to adequately replicate wave properties. The outcomes of our analysis provide several site-specific hints for practical coastal engineering.