Foredune initiation and early development through biophysical interactions.

Coastal dunes result from complex interactions between sand transport, topography and vegetation. However, uncertainty still persists due to limited quantitative analyses, integrating plant distribution and morphologic changes. This study aims to assess the initiation and maintenance of feedback processes by analysing the early development stages of incipient foredunes, combining data on the evolution of the plant cover and communities and dune morphology. Over three years, the monitoring of a newly formed dune (1 ha plot) reveals the progressive plant colonisation and the episodic accumulation of sand around vegetated areas controlled by sediment availability. Distinct colonisation rates were observed, influenced by inherited marine conditions, namely topography and presence of beach wrack. Berm-ridges provided elevations above the critical threshold for plant colonisation and surface roughness, aiding sediment accumulation. Beach wrack above this threshold led to rapid expansion and higher plant concentration. In the initial stages, vegetation cover significantly influenced sediment accumulation patterns, with higher accumulation around areas with high plant cover and low slopes or around areas with sparse vegetation but milder slopes. As the dune system matured and complexity grew, the link between vegetation cover and accumulation became nonlinear. Mid to low coverages (5-30 %) retained most of the observed accumulation, especially when coupled with steep slopes, resulting from positive feedbacks between vegetation, topography and sand transport. As foredune developed, vegetation cover and diversity increased while inherited morphologies grew vertically, explaining the emergence of dune ridge morphological types. Flat surfaces lacking wrack materials experienced a three-year delay in colonisation and sand accumulation, leading to the formation of terrace-type incipient foredunes. These observations underline feedback processes during the early stages of dune formation, with physical feedbacks primarily driving initiation and biophysical feedbacks prevailing in subsequent colonisation stages.

Effectiveness assessment of risk reduction measures at coastal areas using a decision support system: Findings from Emma storm.

Storms impact coastal areas often causing damages and losses at occupied areas. On a scenario of increasing human occupation at coastal zones and under climate change conditions (including sea level rise and increasing frequency of extreme sea levels), the consequences of storms are expected to be amplified if no adaptation or further management actions are implemented. The selection of the best possible coastal management measures, considering both costs and effectiveness, will be mandatory in the future, in order to optimise resources. This work analyses the performance of risk reduction measures (beach nourishment and receptors - house and infrastructures - removal), using a decision support system comprised by a morphodynamic numerical model (XBeach) and a Bayesian network based on the source-pathway-receptor concept. The effectiveness of the risk reduction measures is then assessed by a simple index expressing the consequences to the receptors. The approach was tested at Faro Beach by evaluating its performance for a particular storm, Emma (Feb/March 2018), which fiercely impacted the southern coast of Portugal. The output results from the modelling were compared to field observations of the actual damages caused by the storm. The combined use of both measures or the solely use of the nourishment would avoid almost all observed impacts from this storm. The work is pioneer on demonstrating the use of a decision support system for coastal regions validated against observed impacts for a high-energy storm event. The methodology and the proposed index are adaptable to any sandy coastal region and can be used to test (and improve) management options at a broad number of coastal areas worldwide, minimizing implementation costs and reducing the risk to the occupation and to the people.

Coastal barrier stratigraphy for Holocene high-resolution sea-level reconstruction.

The uncertainties surrounding present and future sea-level rise have revived the debate around sea-level changes through the deglaciation and mid- to late Holocene, from which arises a need for high-quality reconstructions of regional sea level. Here, we explore the stratigraphy of a sandy barrier to identify the best sea-level indicators and provide a new sea-level reconstruction for the central Portuguese coast over the past 6.5 ka. The selected indicators represent morphological features extracted from coastal barrier stratigraphy, beach berm and dune-beach contact. These features were mapped from high-resolution ground penetrating radar images of the subsurface and transformed into sea-level indicators through comparison with modern analogs and a chronology based on optically stimulated luminescence ages. Our reconstructions document a continuous but slow sea-level rise after 6.5 ka with an accumulated change in elevation of about 2 m. In the context of SW Europe, our results show good agreement with previous studies, including the Tagus isostatic model, with minor discrepancies that demand further improvement of regional models. This work reinforces the potential of barrier indicators to accurately reconstruct high-resolution mid- to late Holocene sea-level changes through simple approaches.