Short-term morphodynamics of intertidal bars the case of Areão Beach (Aveiro, northwest Portugal)

Abstract

Intertidal bar morphodynamics were examined at Areao Beach, a mesotidal beach located in the highly energetic Northwest coast of Portugal. A field experiment was carried out in 2002 from February 5 to March 16. During this period topographic surveys were done every three days. Offshore wave data and tidal records were used to evaluate the successive morphological changes. Morphodynamics of the two intertidal bars recorded were characterized by a landward migration over a flattened profile after a previous storm event. Differences in the dimensions of the bars were related to the smaller transported volumes as the storage of sediment at lower foreshore decreased with each bar formation and migration. Intertidal bars presented the following behaviour: formation under low energy wave conditions and significant tidal ranges; stabilisation during neap tides and migration, by successive erosion/accretion series, under greater tidal ranges, while wave climate conditions experienced a progressive increasing; and welding to the beach forming a berm. Boundary conditions coupled to the significant wave height offshore were used to classify each phase of bar evolution: formation phase (1-1.5 m), evolution phase (lower than 2.5-3 m) and decay phase (> 3 m). These considerations were limited to beaches in the area that present well-developed longshore bars.