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Geomorphology and morphodynamics of embayed beaches in contrasting environments

Publication . Ferreira, Carlos Manuel Silva Loureiro Alves; Ferreira, Óscar; Cooper, Andrew

This study investigates the medium-term (months to years) morphodynamic variability of embayed beaches in contrasting geomorphological settings, combining two years of topographic and sedimentary monitoring in six embayments on the southwestern Portuguese coastline (three on the west coast and three on the south coast) with hydrodynamic forcing data explored using statistical and modelling techniques. From a broader, embayment-wide scale, towards a focused, process-oriented scale, the thesis addresses the following points: (i) the classification of morphodynamic state in embayed beaches, (ii) assessment of geological boundaries as constraints on the morphological variability of embayed beaches, (iii) the identification of morphodynamic mechanisms responsible for non-uniform alongshore behaviour in high-energy embayed beaches, and (iv) the development of megarips and their role in enhancing erosion during storm groups. This study demonstrates that: (i) geological control significantly influences embayed beach morphodynamic behaviour; (ii) beach morphodynamic parameters have limited ability to adequately differentiate beach types, particularly within the intermediate domain; (iii) geological boundaries constrain morphological change and promote conspicuous alongshore variability in embayed beaches; (iv) beach rotation processes in south coast embayments and topographically-controlled rip circulation in the west coast embayments are the primary drivers of alongshore non-uniform variability; (v) under high-energy conditions topographically-controlled rips evolve to megarips, which promote significant beach erosion; (vi) the persistence of megarips during storm groups leads to extreme beach erosion, and maintenance of megarip circulation following storms inhibits post-storm beach recovery. Further research is still necessary to improve the present understating of embayed beach morphodynamics, particularly involving detailed field studies of nearshore circulation and morphologic change. Embayed beaches frequently present site-specific behaviour and knowledge of their dynamics is fundamental to improve both beach safety and management.

2012Doctoral thesis

Open Access