A Nearshore Wave Energy Atlas for Portugal

The nearshore wave energy resource in Portugal has been assessed through the development of ONDATLAS. This is an electronic atlas, compatible with Internet access, containing comprehensive wave climate and wave energy statistics for 78 points at about 20 m water depth spaced variably ca. 5 km to 30 km, 5 points at deep water and 2 points at open ocean locations. The data were produced by a third-generation wind-wave model, complemented by an inverse-ray model that computes the directional spectra transformation from open ocean to the near-shore. Shoaling, refraction, bottom dissipation and shelter by the coastline and/or neighbouring islands are taken into account. ONDATLAS statistics comprise yearly and monthly values, variability and probability data for significant wave height, energy (mean) period, peak period and wave power, and directional histograms for wave and power direction. Joint probability distributions for various combinations of the above parameters are also available, as well as extreme values and return period for wave height and period parameters. A summary of the detailed verification of this model using long-term buoy measurements at four sites is presented. The main characteristics of ONDATLAS are described. The strong spatial variability that wave conditions exhibit at the coastal area are illustrated and a brief assessment of the nearshore resource at the Portugal mainland is presented.