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- CRAF Phase 1, a framework to identify coastal hotspots to storm impactsPublication . Ferreira, Óscar; Viavattene, Christophe; Jimenez, Jose; Bole, Annelies; Plomaritis, Theocharis; Costas, Susana; Smets, StevenLow-frequency high-impact storms can cause flood and erosion over large coastal areas, which in turn can lead to a significant risk to coastal occupation, producing devastation and immobilising cities and even countries. It is therefore paramount to evaluate risk along the coast at a regional scale through the identification of storm impact hotspots. The Coastal Risk Assessment Framework Phase 1 (CRAF1) is a screening process based on a coastal-index approach that assesses the potential exposure of every kilometre along the coast to previously identified hazards. CRAF1 integrates both hazard (e.g. overwash, erosion) and exposure indicators to create a final Coastal Index (CI). The application of CRAF1 at two contrasting case studies (Ria Formosa, Portugal and the Belgian coast), validated against existing information, demonstrates the utility and reliability of this framework on the identification of hotspots. CRAF1 represents a powerful and useful instrument for coastal managers and/or end-users to identify and rank potential hotspot areas in order to define priorities and support disaster reduction plans.
- Towards assessing the resilience of complex coastal systems: examples from Ria Formosa (South Portugal)Publication . Kombiadou, Katerina; Matias, Ana; Carrasco, Rita; Ferreira, Oscar; Costas, S.; Vieira, G.The present paper contributes to assessing the resilience of a complex barrier island environment, namely of the Ria Formosa multi-inlet system in southern Portugal. The long-term morphologic evolution of four study areas during the last 60 years (1947 to 2014) is analysed based on aerial photographs, including the environments of oceanic and backbarrier beaches, dunes and salt marshes. The results show that each study area responded to external drivers (inlet stabilisation works, storms, etc.) differently, evolving in distinct patterns during the study period. All four study areas appear resilient to external pressures and/or forcing conditions, since they are either transforming (Barreta and Culatra islands), or adapting (Cabanas island and Cacela peninsula) or remaining stable at a near-equilibrium state (Tavira island). Based on the analysis of the multi-decadal evolution of the sites, four resilient barrier states are identified, related to the maturity and growth of the barrier. In the next stages, the research will focus on the relation between medium to short-term changes, aiming at understanding the response and feedbacks of the environments to specific drivers of change and relating them to resilience indicators.
- Biotic and abiotic factors governing dune response to storm eventsPublication . Garzon, Juan L.; Costas, Susana; Ferreira, OscarThe alongshore response of dunes to storm events can be extremely variable and,consequently, their capacity to maintain their services, including the protection ofhinterland communities. In this study, the role of biotic and abiotic factors determin-ing the magnitude of dune retreat driven by a severe storm along a 60 km barrierisland system was investigated. Data from high-resolution satellite imagery, digitalterrain models, and wave propagation models were used in this assessment. Theassessed abiotic factors included the backshore volume, dune height, downdrift inletdistance, and incident wave power. The evaluated biotic factor was the vegetationcover, characterized by a vegetation index retrieved from the multispectral imagery.The results revealed large alongshore variability on dune retreat, ranging from negli-gible impact to ca. 40 m of retreat. All combined factors allowed us to explain up to70% of the dune retreat variability through a multi-regression analysis. Among allinvestigated factors, the major contributor controlling the magnitude of dune retreatwas the backshore volume (more robust berms reduced the retreat) followed by thewave power (normal and longitudinal components). Moreover, the removal of localsalient features in the dune line caused the straightening of the coastline, highly con-tributing to the development of dune retreat hotspots. The other evaluated factorshad a smaller influence on reducing coastal retreat, including the vegetation, whosecontribution to dune protection was around one order of magnitude lower than thatprovided by the backshore volume. The results highlight the importance of regionalassessments to understand the causes behind the large alongshore variability ofstorm impacts at dunes. They also state the relatively low influence of the vegetationfrom this climatic region to enhance dune resistance to storms.
- Sense of place, risk perceptions and preparedness of a coastal population at risk (Faro Beach, Portugal): a qualitative content analysisPublication . Domingues, Rita B.; Costas, Susana; Jesus, Saúl; Ferreira, ÓscarFaro Beach, a heavily urbanized settlement in Ria Formosa, southern Portugal, is highly vulnerable to coastal hazards, namely beach erosion and overwashes caused by storms, that have resulted in house and road damage on several occasions. Despite the risks, local residents accept to live there. Four semi-structured interviews were conducted to understand residents’ beliefs, risk perceptions and preparedness regarding coastal risks. We used a qualitative content analysis to derive manifest contents from the interviews. Three main themes were identified in the interviews: how residents feel about Faro Beach; how they perceive coastal hazards and risks; and how they deal with those risks. Positive feelings regarding Faro Beach were identified in all residents, reflecting a strong sense of place that includes high levels of place attachment, rooting, sense of community and place identity. Residents’ personal experiences with hazards probably undersized their perceptions regarding the risks that they are exposed to. Their willingness to participate in disaster risk reduction measures seemed associated with behavioral barriers driven by mistrust in authorities and externalization of responsibility. Residents also revealed low levels of preparedness towards coastal hazards, probably due to their low risk perceptions and their perception of threats as distant in time.
- Satellite derived shorelines at an Eexposed meso-tidal beachPublication . Cabezas-Rabadan, Carlos; Pardo-Pascual, Josep E.; Palomar-Vazquez, Jesus; Ferreira, Oscar; Costas, SusanaShoreline position data offer extremely valuable information for understanding coastal dynamism and beach changes. This research applies SHOREX system for defining the shoreline position from free mid-resolution Landsat-8 (L8) and Sentinel-2 (S2) satellite imagery. This system allows an automatic definition of Satellite Derived Shorelines (SDS) over large regions and periods. Accuracy and utility of the resulting SDS have been previously assessed with positive results at low energy, microtidal, Mediterranean beaches. This work assesses SDS extracted using SHOREX at a mesotidal and moderate to highly (during storms) energetic environment, namely at Faro Beach, a barrier beach located in Ria Formosa (Algarve, South Portugal). Accuracy was defined for 14 SDS derived from S2 and 10 from L8 by measuring the differences in position with respect to the shoreline inferred from profiles obtained on close dates (or simultaneously) to imagery acquisition. For non-simultaneous datasets, the water level was estimated for the time of the satellite images acquisition using oceanographic data and run-up formulations. The measured and estimated shoreline positions were then compared with the extracted SDS. The overall accuracy is good, with errors about 5 m RMSE, supporting the application of the used methodology to define shoreline dynamics and evolution at challenging environments, as mesotidal exposed and dynamic beaches.
- Relatório setor segurança de pessoas e bens: vulnerabilidades atuais e futurasPublication . Ferreira, Andreia; Oliveira, André; Dias, Luís Filipe; Fernandes, Luís; Brito, David; Braunschweig, Frank; Sampath, Ruwan; Moura, Delminda; Mendes, Isabel; Carrasco, A. Rita; Costas, Susana; C. Veiga-Pires, C.As alterações no clima constituem um fator a ter em conta no setor da segurança de pessoas e bens. Muitos dos impactos associados às alterações climáticas exacerbam ou alteram ameaças já existentes, como aquelas associadas a eventos extremos, inundações e secas (Sperling e Szekely, 2005). Os cenários de alterações climáticas projetados para Portugal tornam necessário um esforço de adaptação do Sistema de Proteção Civil face à probabilidade do aumento da ocorrência de eventos meteorológicos extremos, na medida em que poderá ocorrer um aumento de fenómenos em que a segurança de pessoas e bens seja colocada em causa. A este nível, a Estratégia Nacional de Adaptação às Alterações Climáticas (ENAAC) indica que as medidas de adaptação face às alterações climáticas, no contexto da segurança de pessoas e bens, se devem desenrolar em duas principais linhas de atuação.
- The role of climate, marine influence and sedimentation rates in late-Holocene estuarine evolution (SW Portugal)Publication . Costa, Ana Maria; Freitas, Maria da Conceicao; Leira, Manel; Costas, S.; Costa, Pedro J. M.; Andrade, Cesar; Bao, Roberto; Duarte, Joao; Rodrigues, Aurora; Cachao, Mario; Araujo, Ana Cristina; Diniz, Mariana; Arias, PabloEstuaries are sensitive to changes in global to regional sea level, to climate-driven variation in rainfall and to fluvial discharge. In this study, we use source and environmentally sensitive proxies together with radiocarbon dating to examine a 7-m-thick sedimentary record from the Sado estuary accumulated throughout the last 3.6 kyr. The lithofacies, geochemistry and diatom assemblages in the sediments accumulated between 3570 and 3240 cal. BP indicate a mixture between terrestrial and marine sources. The relative contribution of each source varied through time as sedimentation progressed in a low intertidal to high subtidal and low-energy accreting tidal flat. The sedimentation proceeded under a general pattern of drier and higher aridity conditions, punctuated by century-long changes of the rainfall regime that mirror an increase in storminess that affected SW Portugal and Europe. The sediment sequence contains evidence of two periods characterized by downstream displacement of the estuarine/freshwater transitional boundary, dated to 3570-3400 cal. BP and 3300-3240 cal. BP. These are intercalated by one episode where marine influence shifted upstream. All sedimentation episodes developed under high terrestrial sediment delivery to this transitional region, leading to exceptionally high sedimentation rates, independently of the relative expression of terrestrial/marine influences in sediment facies. Our data show that these disturbances are mainly climate-driven and related to variations in rainfall and only secondarily with regional sea-level oscillations. From 3240 cal. BP onwards, an abrupt change in sediment facies is noted, in which the silting estuarine bottom reaches mean sea level and continued accreting until present under prevailing freshwater conditions, the tidal flat changing to an alluvial plain. The environmental modification is accompanied by a pronounced change in sedimentation rate that decreased by two orders of magnitude, reflecting the loss of accommodation space rather than the influence of climate or regional sea-level drivers.
- Regional assessment of storm related overwash and breaching hazards on coastal barriersPublication . Plomaritis, Theocharis A.; Ferreira, Óscar; Costas, SusanaCoastal communities are threatened by the impact of severe storms that may cause significant loss of life and damage to properties. Among the main processes behind such impacts on coastal barriers are the occurrence of overwash and breaching during storm events. In order to estimate potential losses associated with a particular event, the above processes must be properly parameterized. Here, we propose a novel methodology to estimate overwash and breaching hazards suitable for a regional scale analysis (Ø 100 km). For the overwash hazard assessment, the method is based on the application of the approach developed by Donnelly (2008) that allows the parametrisation of the overwash hazard considering both flow velocity and flow depth. Moreover, the inland extension of the associated hazard, which is critical to assess subsequent vulnerability, can also be estimated following this methodology. The proposed method requires the selection of a runup formula validated for the study area, a storm beach profile, a runup lens angle, and a percolation constant for infiltration. To assess the breaching, hazard, a new multivariable evaluation is proposed that allows ranking the potential of breaching. The multivariable evaluation combines overwash and erosion hazards as well as their extensions with the main morphological characteristics of the barrier, resulting in the breaching hazard index, that ranks from 0 to 5 (no breaching to inlet formation). Inland breaching extension is also relevant for the vulnerability assessment. The breaching extension can be estimated using historical or contemporary analogues of the nearest flood deltas. The developed approaches were applied to Ancão Peninsula (Algarve, Portugal) as a demonstration example. The advantages of the present approach are: adaptability to various environments where overwash and/or breaching processes are important, time efficiency on evaluating overwash and breaching hazards, and the assessment of hotspot areas at a regional scale.
- Effect of survey parameters on unmanned aerial vehicles-derived topography for coastal dune monitoringPublication . Bon de Sousa, Luísa; Costas, Susana; Ferreira, ÓscarCoastal dunes are fragile ecosystems emerging at the interface between marine and continental environments. They provide multiple services, among which are the protection against the impact of storms and the hosting of diverse and unique species of fauna and flora. However, changes in the topography or biological component of these systems may endanger the perpetuation of service provision. Topographic changes within dunes can significantly differ in magnitude depending on the type of process (i.e., marine or aeolian) and the temporal scale of analysis (event to annual scale), making their monitoring a challenging task. In recent years, unmanned aerial vehicles (UAVs) have been increasingly used to monitor coastal dunes, proving to be a cost-efficient methodology for the collection of topographic data. Yet, the application of UAVs in combination with the structure from motion approach to obtain digital surface models (DSMs) presents some limitations related to the level of accuracy provided for the evaluation of topographical changes in dunes with low sedimentation rates. This work explores different survey configurations using UAVs flying at low altitudes with the aim of obtaining high-quality DSMs with vertical accuracies preferably around or lower than 0.04 m. Several tests were performed to evaluate the influence of different parameters on the accuracy of the DSM, including flight altitude and orientation, density and spatial distribution of ground control points (GCPs), terrain slope, vegetation cover, and sun-related parameters. The results indicate that the intended accuracies can be obtained by combining overlapped perpendicular flights, GCPs distributed regularly following a diamond grid, with densities of at least 6 GCPs per hectare, sun altitudes between 30 and 40 deg, and a total solar radiation per hour between 1750 and 2250 KJ / m(2). In addition, better results were obtained across gentle slope areas, suggesting the eventual need to adapt to the particularities of each site to ensure the accuracy.
- Coastal ridge constructive processes at a multi‐decadal scale in Barreta Island (southern Portugal)Publication . Herrero, Xabier; Costas, Susana; Kombiadou, KaterinaMultiple ridges across prograding coasts may display variable geometries, commonly expressed through varying elevations. Changes in ridge elevation have been traditionally related to the occurrence of fluctuating progradation rates, which might, in turn, be driven by shifting environmental conditions. Here, we explore the geometry and growth mechanisms of multiple ridges, generated at Barreta Island (Ria Formosa, southern Portugal), as a consequence of the rapid progradation of the island over the last 70 years, following the artificial fixation of the downdrift Faro-Olhao inlet with jetties in 1955. The variability in the morphology of these features was analysed in combination with available wind and wave data, in order to better distinguish growth mechanisms and understand the main parameters determining the final geometry of the observed ridges. The results suggest that (1) most of the identified ridges fall in the beach ridge classification, as they have been mostly built by marine processes, and (2) the parameters derived from, or closely related to wave climate variability (e.g. progradation rates, storm occurrence) can jointly explain most of the observed morphological changes, while aeolian processes played a secondary role. Indeed, ridge geometry appears mainly controlled by progradation rates, with higher ridges associated with lower progradation rates. Progradation rate, in turn, is mostly related to longshore wave power, storminess, and the occurrence storm groups. Yet, the final configuration of ridges can also be affected by runup levels and onshore winds. Therefore, establishing the relation between ridge geometry and wave climate is not a straightforward task, because of the complex processes and interactions that control coastal morphodynamics.