Aeolian sediment transport enhanced by storms and human pressure at coarse sandy barrier islands

Résumé

Traditionally, enhanced aeolian activity has been associated both to human derived disturbances in the vegetation cover and to the impact of storminess periods responsible for intense winds and thus enhanced dune mobility. Here, we investigate the positive impact that both factors may have on aeolian sediment transport by directly affecting the beach surface armouring, a major inhibition factor at coarse sandy coastal barriers. For that, we explore the foredune along the sandy peninsula of Ancão, at Ria Formosa barrier island system, Southern Portugal, using the local winds and a series of digital terrain models between 2009 and 2017 in order to identify the areas of aeolian accumulation. We have found that the main factor that determines the growth of foredunes at the study area is beach progradation by providing both accommodation space and sediment. Our results also suggest that the transference of sand to the adjacent foredune is highly inefficient most likely due to the rapid armouring of the backshore surface. Therefore, aeolian sediment transport to the foredune at the study area was associated to the destruction of the armouring effect through backshore disturbance induced by (i) the impact of successive storms over the beach, eroding and renewing the backshore surface, or (ii) the human pressure associated to beach visiting through the year.