Aeolian sediment transport potentials and dune evolution in Ancão peninsula (Ria Formosa), Portugal

• Autor(a) principal: Pliatsika, Dimitra Alkisti
• Data de Publicação: 2018
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10400.1/12356
• topic: Aeolian sediment; Transport potentials; Dune evolution; Ancão peninsula

In the present study is attempted to examine aeolian sediment transport potential and to determine the constituents that promote/restrict the dune system development of Ancão Peninsula, where, apparent alongshore geomorphological differences, i.e. western and eastern sector, exist. In this study were investigated: wind potential for sediment transfer over the last 20 years (1997-2016) using recent granulometric data, dune morphology and elevation changes obtained from RTK-GPS beach profiles (2016), volumetric changes in three backshore polygons extracted from Lidar and UAV datasets (2009-2011 and 2011-2016) in both sectors. Presence of species communities of vegetation and shoreline evolution rates (1958-2014) as an indirect indicator for dune morphology were also used. Additional key parameters, namely littoral drift, updrift nourishment interventions and effect of Ancão Inlet were also considered. A windy event was defined at velocity above 8.9 m/s for a mean beachface grain size of 466 μm. Accounting for onshore winds and steering of the peninsula, only 1.7% of the winds was responsible for potential sediment transport. Moreover, the wind records, revealed that the windier years for potential transfer were 2002 (1.7 m3/m), 2009 (2.1 m3/m) and 2010 (1.8 m3/m). Shoreline evolution showed negative values (retreat) for the western and central sector of the peninsula (-0.2 m/yr and -0.25 m/yr respectively) and accretional (+0.79 m/yr) for the eastern. The volume change rates for 2009-2011 show accumulation with very low positive values for the western sector that progressively increase towards the eastern (from eastern polygon: 0.85 m3/(m.yr) to western: 7.32 m3/(m.yr)). The vegetational communities in the two sectors are compatible to the respective morphologies. In the western sector the absence of typical embryo dune vegetation (e.g. Elymus farctus, Eryngium maritimum) conforms with the absence of new foredune development. In the western part of the eastern sector, sparse embryo dune vegetation with low density is present, whereas in the most eastward part of the peninsula -in the inlet vicinity- two seaward developing foredunes are formed. Assembling all elements, it is concluded that the mild wind regime in conjunction with the existing coarse grain size permits the development of relatively small dunes. In the western sector the vegetation suggests dune maturity, however the updrift nourishments have contributed to shoreline stabilization and subsequently to restriction of dune erosion. On the eastern sector nevertheless, the presence of Ancão inlet fostered creation of accommodation space through shoreline progradation, and hence incipient dune vegetation and new embryo dunes formation.