The use of numerical models as complement of wave measurements in Amoreira Beach, Aljezur

Abstract

To characterize the hydrodynamics of the Aljezur Stream, which flows to the Amoreira beach (in the South-western coast of Portugal), and its impact on the water exchange with the sea, an estimation of the local wave climate was judged necessary. Therefore, both in-situ wave measurements and coastal wave propagation models, forced offshore by the results of the WaveWatch III (WWIII) regional wave model (Tolman, 2002), were used. Three field campaigns were conducted to take measurements of the free surface elevation on the Amoreira beach. The data processing and analysis were obtained by applying classical time and spectral domain techniques. These allowed the computation, for each record, of equivalent parameters of significant wave height (HS and HM0, for time and spectral analyses respectively) and mean wave periods (Tmed and TZ, for time and spectral analyses respectively), which, alone or together, are useful to estimate the representative characteristics of the waves at the site. However, these measurements, although being very useful to describe local wave characteristics, are of too short duration to characterize the long-term wave climate, and they also suffer from a restricted spatial representation of the wave conditions. Therefore, the NOAA archives of the WWIII model were used to produce offshore boundary conditions to the spectral wave propagation model SWAN (Booij et al., 1999), which was used in this paper as complement of the in-situ measurements, enabling a better local wave climate characterization to be found. This paper describes the measurement campaigns, the data analyses made, and the methodology for the characterization of wave conditions from offshore to inshore and its application to the study area using SWAN model. A comparison between measured and numerical data is finally made. The results from this comparison may be useful to assist the coastal management decision-making