Field determination of sediment transport patterns: a case study from Patos Beach (Northwest Spain)

Abstract

Transport patterns at Patos Beach, in the Northwest of the Iberian Peninsula, were studied by performing different field experiments under various spatial and time scales. For the purpose of the present work, the central part of the beach was selected, where the highest morphodynamic changes occurred. Monthly monitoring consisting on beach profile surveys and sediment sampling were carried out from November 1999 to February 2001. Detailed fieldwork were conducted on 18-19 September 2000, during two tidal cycles, in order to acquire specific data from topography, fluorescent tracers and mixing depth experiments. Seasonal study shows a great variation, ranging from reflective to dissipative morphodynamical states, according with the prevailing wave climate. Temporal evolution of the beach morphology, volumetric and sedimentary variations presented no significant longshore changes, confirming cross-shore transport as the main pattern in the beach. The short-term study reinforces this assumption. Results obtained from the short term analysis (topographic evolution and tracer distribution) agree with the medium term trends approach and revealed the existence of weak transport rates towards onshore direction, under calm conditions, pointing out to a very gradual recovery of the beach.