Effect of the Sea Level Variation in the Offshore Limit of the Surf Zone of Buarcos, Portugal

Abstract

The variation of the position of the outer limit of the surf zone of Buarcos with the tidal level, in the West coast of Portugal, was estimated based on numerical modelling. The position of the breaker line, dependent on the wave characteristics, water depth and the sea bottom geometry, was estimated for a group of monochromatic waves representative of the local wave regime at three sea levels, representative of mean high water, mean water level and mean low water. The sea bottom geometry of the area of study, characterised by the existence of a discontinuous set of irregular hard rock outcrops in the nearshore and foreshore zones, is responsible for the particular features of the local wave transformation process and sediment dynamics. A two-dimensional numerical model of wave propagation, based on the mild-slope equation, that simulates wave transformation due to the simultaneous occurrence of the physical processes of refraction, diffraction, reflection and breaking, was applied. The results obtained allowed to identify the breaker line position and to acknowledge its variation as function of the sea level and the representative wave regime.