Modeling wind waves and wave exposure of nearshore zones in medium-sized lakes

We determine wind-wave properties and estimate the wave exposure along the entire shore of Lake U¨ berlingen, a subbasin of Lake Constance, using a third-generation spectral wave model (SWAN), and compare results to field data on surface waves at three different sites and to predictions from a simple fetch-based model (FETCH). Forcing the models with local wind data measured at a meteorological station in the center of Lake U¨ berlingen provides better simulation results than a spatially resolved wind field obtained from the numerical weather system of the Consortium for Small Scale Modeling (COSMO). Because wave diffraction is considered in SWAN but not in FETCH, SWAN provides on average higher wave heights than FETCH and agrees better with observations for waves with heights above 0.15 m. Wave exposure, that is, the frequency of occurrence of wind waves with heights above 0.15 m, varied substantially between different sites along the shore even at small spatial scales. Although the general pattern of wave exposure was similar for simulations with SWAN and FETCH, the model results differed at specific sites, especially at bays and headlands, and also with respect to the absolute values for wave exposure and its variation between sites. Simple fetch models may be insufficient to reliably quantify the spatial variability of wave exposure at small spatial scales, and complex wave models such as SWAN may be required even in medium-size lakes