Morphodynamic response to extreme wave events of microtidal dissipative and reflective beaches

Abstract

In this work, the morphodynamic response of microtidal dissipative and reflective beaches to extreme wave events generated by hurricanes and cold fronts in the Colombian Caribbean was established. Two sandy beaches were used as case studies, Bocagrande (Cartagena, Bolívar Department) (dissipative) and Costa Verde (Ciénaga, Magdalena Department) (intermediate–reflective). The numerical models SWAN and XBeach were used to investigate wave propagation during storm conditions for selected cases and to determine morphological changes on the two beaches. Both models were calibrated using hydrodynamic and bathymetric data obtained in field campaigns pre and post-cold fronts. The results of the numerical models satisfactorily represented the real conditions on both beaches. It was shown that regardless of beach configuration, whether dissipative or intermediate–reflective, erosive processes had a greater magnitude during cold fronts (March 2009 and December 2017) than under hurricanes conditions. Bocagrande beach is more exposed to extreme wave events, mainly due to its characteristic dissipative profile. Infragravity wave energy, fundamental in sediment transport dynamics, is not reflected on the beach front, but is dissipated along the swash zone and drags sediment to the sea. By contrast, Costa Verde shows conservative coastline retreats: its intermediate–reflective morphologic configuration played a transcendental role. Infragravity wave reflection on the beach front does not allow a longer water extension over dry areas in the swash zone under storms.