Usually there is little knowledge of long-term wave conditions at prospective sites for wave-power plants, while the deep-water or open sea conditions may be more known and geographically less varying. However, many wave-energy plants are intended for water depths small compared to the wave length. A concept for assessing design waves at a near-shore site is to transform the off-shore wave spectra to the target site by a model for spectral wave-energy transfer over the actual bottom topography. The inshore spectra can be used for linear statistics of extreme waves, design wave loads and for assessment of power take off. In this context it is important to know the realism of used spectral forms.
Based on 58 measured wave spectra at 6 m water depth at the near-shore wind farm Bockstigen in the Baltic the most realistic spectrum was found to be the TMA spectrum, which is a JONSWAP spectrum modified for shallow water. Some few examples are given. Normally wave-energy devices would be placed in somewhat deeper water and water depth correction will be smaller