Effect of coastal waves on sea level in Óbidos Lagoon, Portugal

Abstract

This study reports the role of waves, tide, wind and freshwater discharges over the sea level in Óbidos Lagoon, a coastal system connected to the sea through a narrow and shallow mobile inlet. To address the hydrodynamic features of this coastal system, the relative importance of different physical forcings were evaluated. For this purpose, observations together with realistic and idealized numerical modeling were used. Both model and measurements show that the lagoon sea level remains above offshore sea level during storm wave periods. Hence, a simplified inlet-lagoon idealized model was described through mathematical expressions, to understand and highlight the physical processes responsible for sea-level elevation. In general, it can be concluded that multiple forcing conditions, specifically tide and waves, are important in defining the dynamics of the Óbidos Lagoon. The variability of the lagoon sea level is 80% due to tide and 20% due to waves. A correlation was found with wave height and sea-level elevation during high wave activity periods; no correlation was found for low wave activity. A significant super-elevation on lagoon sea level occurs during storm wave periods. Such super-elevation is explained, not only by wave set-up or radiation stresses due to waves, but also by tidal inlet morphology (mainly depth and length).