Browsing by Author "Matias, Ana"
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- An evolutionary categorisation model for backbarrier environmentsPublication . Carrasco, Ana Rita; Ferreira, Oscar; Davidson, M.; Matias, Ana; Dias, J. A.Shorelines occurring along restricted fetch environments, such as the backsides of barrier islands, are extremely diverse with respect to their morphologic characteristics and evolution. In order to better understand the morphodynamic evolution of backbarriers and the associated implications for entire barrier systems, this study proposes a backbarrier evolutionary categorisation model based on the development of two types of index: backbarrier evolution tendency and backbarrier maturation condition. The proposed characterisation system is applied to the Ria Formosa backbarrier (located in southern Portugal) for the period 1947 to 2001. Cross-shore and longshore backbarrier trends in Ria Formosa suggest a shrinking of the lagoon system as a consequence of a decrease in the coastal length of the backbarrier coastline and a landward displacement of it. Even though some of the backbarriers examined were found to be in an immature state, the results obtained illustrate a maturing trend for the system overall. Barriers in Ria Formosa fall into two main evolutionary categories: backbarrier reduction and backbarrier growth. This means that neither smoothing nor branching has been significant and therefore that backbarrier recent evolution is closely related to barrier coast length. Application of the proposed characterisation to the Ria Formosa case study has helped reveal backbarrier evolutionary trends and therefore should be of use in the management of backbarrier systems.
- Backbarrier evolution at a medium-term scalePublication . Carrasco, Ana Rita; Ferreira, Óscar; Matias, Ana; Freire, Paula; Dias, J. A.This study reports the medium-term evolution of a sandy backbarrier and its relation with prevailing wind conditions. Obtained results demonstrated that Ancão backbarrier does not behave as a scale-down version of higher energy fetch-limited or oceanic beaches, being considered as a low-energy beach with extremely low wind-induced wave conditions. Volumetric changes during the three years monitoring were small, and the analysis of low-scale changes was divided into four beach compartment: upper beach, beach face, tidal flat, sand bank. There was no significant correlation between prevailing wind conditions, volume and grain-size variation, neither a marked seasonal pattern. Some wind-induced beach changes were perceptive in the grain size variations, related mostly to aeolian offshore sediment transport. Morphological changes were similar in the upper part of the profile, including upper beach and beach face, with changes mostly related to wind and windwaves energy. The lower part of the profile, which includes the tidal flat and the sand bank, frequently react independently from the upper part of the profile, although, sediment exchange between them was noticed during extreme conditions. The lower part of the profile had larger volumetric variability, without any evident wind dominance. The studied beach revealed high morphologic resilience, yet the overall quantities of sediment transported between 2005 and 2008 has particular relevance in the local coastal management context. Further research is needed to develop a broad-scale model of fetch-limited beaches, including the less energetic settings of the spectra such as backbarrier environments.
- Backbarrier shores along the Ria Formosa lagoonPublication . Carrasco, A. Rita; Matias, AnaLow energy beaches are located in sheltered and fetch-limited environments. The fetch, also called the fetch length, is the uninterrupted distance over the sea surface for which the wind can blow without a change in direction and affects the growth of wind-waves. Fetch-limited beaches are found in estuaries and bays (e.g. Chesapeake Bay, USA), behind ocean barriers (e.g. Pamlico Sound, USA), adjacent to inlets (e.g. Tapora Bank, New Zealand), deltas (e.g. Menderes River, Turkey), eroding thermokarst (e.g. Yensei Bay, Russia), and glacial outwash fans (e.g. Canal Baker, Chile; Cooper et al., 2007). In the case of barrier island systems, the back of barrier islands facing the lagoon environments i.e., backbarrier shores are fetch-limited environments. A barrier is an elongated ridge that is composed predominantly of unconsolidated sand and/or gravel and protect the adjacent mainland from open-water processes (Figure 2.1). From the sea to the mainland, the barriers are generally composed of the shoreface, dune and backbarrier environments, and they are separated alongshore by tidal inlets (Figure 2.1). Barrier islands are dynamic systems, constantly on the move, migrating under the influence of waves, tides, currents, storms, and changing mean sea levels. The backbarrier is a narrow, elongated, intertidal landform that is located on the lagoon or estuary side of the barrier island and can take the form of sandy beaches, tidal flats or salt marshes (Figure 2.1). Backbarrier beaches tend to be morphodynamically reflective (according to the classification of Wright & Short, 1984), with steep narrow foreshores that have smaller seasonal variations than open ocean beaches. The tidal flat is bound to the foreshore and might end in a salt marsh fringe. Salt marshes are among the most productive ecosystems on earth.
- Barrier island resilience assessment: Applying the ecological principles to geomorphological dataPublication . Kombiadou, Katerina; Matias, Ana; Costas, Susana; Carrasco, A. Rita; Plomaritis, Theocharis A.; Ferreira, ÓscarApplying the ecological resilience principles to barrier island geomorphological evolution requires approaches that perceive and interpret resilience far from predefined barrier characteristics and static views. Accepting that barrier islands, like all natural systems, are dynamic and adaptively changing in response to external disturbances is fundamental to the formulated approach. To this aim, geomorphological units and dimensions were used to describe barrier island stability landscape as an actively shifting ‘topography’, reshaping in response to exogenous events and in relation to intrinsic properties. The structure of the subaerial barrier was characterised using the environmental units of Beach, Dune and Marsh (or BDM), where different combinations of BDM structure define distinct barrier stable states, under a simplified framework that is applicable over a wide range of barrier structures. The methodology is based on reconstructing resilience trajectories of barrier islands through identifying the distinct BDM states and related shifts (thresholds crossed) and assessing resilience dimensions (latitude, resistance and precariousness defined as barrier width and height and proximity to mainland, respectively) that, jointly, define the shape of the stability domain. The approach was applied to the Ria Formosa barrier island system (S. Portugal), using multi-decadal geomorphological data and gradually decreasing spatial discretisation, passing from individual barrier transects to sectors and to entire barriers. The joint evolution of two inland-migrating barriers (Cabanas Island and Cacela Peninsula) was used as an exemplar of adaptive capacity in barrier geomorphic change and, therefore, of resilient response to external pressures. Resilience pathways showed that the Ria Formosa barriers have been resilient over the studied timeframe, with a tendency for maintaining or increasing BDM structural complexity. In general, the stability domain tends to shift from low latitude and high resistance forms (narrow-deep basins of attraction) in the west part of the barrier chain, to higher latitudes and lower resistance ones (wide-shallow basins) towards the east. Precariousness peaks near the edges of the system (low lagoon width) and minimises towards the central part (most detached barriers). Scaling issues regarding smoothing of longshore variability and potential consequences on masking thresholds and critical dimensions are highlighted and discussed, along with the key role of the meaning of specified resilience (of what?) in the assessment. The methodology is a novel approach, easily transferable to different systems and spatiotemporal scales of analysis, representing a step forward in interpreting and assessing barrier island resilience.
- Bridging the gap between resilience and geomorphology of complex coastal systemsPublication . Kombiadou, Katerina; Costas, Susana; Carrasco, A. Rita; Plomaritis, Theocharis; Ferreira, Oscar; Matias, AnaResilience has been used over a wide range of scientific fields and often ambiguously, causing confusion over terminology and concepts and giving rise to distinct interpretations and misconceptions, even within the same scientific discipline. Starting by providing clarifications and definitions of the main terminology and key principles of ecological resilience theory, we pass on to expressing them through geomorphic dimensions of barrier islands. Three distinct environments (beach, dune, marsh) are proposed as the panarchical levels of analysis, along with potential feedbacks between them and geomorphic dimensions that can express the changes of the stability landscape. Morphological changes induced by storms and subsequent recovery are transferred to stability landscapes, over a range of storm impacts and recovery. We postulate that postperturbation recovery should not be restricted to regaining pre-disturbance barrier dimensions, but should be viewed in terms of reorganisation and adaptation, accounting for maintaining the existence of functions, or the ability of the system to regain them. The proposed scheme and dimensions are tested using geomorphological data from barrier response to distinct disturbances, over different temporal scales that range from event to multi-decadal ones. The case of a barrier island migrating landwards is conceptualised in terms of alternative states and thresholds arising during the process and related phases and changes to the adaptive cycle. The methodology and approach presented is a step towards more holistic views of geomorphic systems’ resilience that we hope will contribute to furthering interdisciplinary understanding and cooperation in the area of sustainability and resilience of natural systems.
- Comparative complete scheme and booster effectiveness of COVID‐19 vaccines in preventing SARS‐CoV‐2 infections with SARS‐CoV‐2 Omicron (BA.1) and Delta (B.1.617.2) variants: A case–case study based on electronic health recordsPublication . Kislaya, Irina; Peralta‐Santos, André; Borges, Vítor; Vieira, Luís; Sousa, Carlos; Ferreira, Bibiana; Pelerito, Ana; Gomes, João Paulo; Leite, Pedro Pinto; Nunes, Baltazar; Machado, Ausenda; Rodrigues, Ana Paula; Peixoto, Vasco Ricoca; Casaca, Pedro; Fernandes, Eugenia; Rodrigues, Eduardo; Ferreira, Rita; Isidro, Joana; Pinto, Miguel; Duarte, Sílvia; Santos, Daniela; Meneses, Luís; Almeida, José Pedro; Matias, Ana; Freire, Samanta; Grilo, TeresaBackground: Information on vaccine effectiveness in a context of novel variants of concern (VOC) emergence is of key importance to inform public health policies. This study aimed to estimate a measure of comparative vaccine effectiveness between Omicron (BA.1) and Delta (B.1.617.2 and sub-lineages) VOC according to vaccination exposure (primary or booster). Methods: We developed a case–case study using data on RT-PCR SARS-CoV2-positive cases notified in Portugal during Weeks 49–51, 2021. To obtain measure of comparative vaccine effectiveness, we compared the odds of vaccination in Omicron cases versus Delta using logistic regression adjusted for age group, sex, region, week of diagnosis, and laboratory of origin. Results: Higher odds of vaccination were observed in cases infected by Omicron VOC compared with Delta VOC cases for both complete primary vaccination (odds ratio [OR] = 2.1; 95% confidence interval [CI]: 1.8 to 2.4) and booster dose (OR = 5.2; 95% CI: 3.1 to 8.8), equivalent to reduction of vaccine effectiveness from 44.7% and 92.8%, observed against infection with Delta, to 6.0% (95% CI: 29.2% to 12.7%) and 62.7% (95% CI: 35.7% to 77.9%), observed against infection with Omicron, for complete primary vaccination and booster dose, respectively. Conclusion: Consistent reduction in vaccine-induced protection against infection with Omicron was observed. Complete primary vaccination may not be protective against SARS-CoV-2 infection in regions where Omicron variant is dominant.
- Detailed investigation of overwash on a gravel barrierPublication . Matias, Ana; Blenkinsopp, Chris E.; Masselink, GerdThis paper uses results obtained from a prototype-scale experiment (Barrier Dynamics Experiment; BARDEX) undertaken in the Delta flume, the Netherlands, to investigate overwash hydraulics and morphodynamics of a prototype gravel barrier. Gravel barrier behaviour depends upon a number of factors, including sediment properties (porosity, permeability, grain-size) and wave climate. Since overwash processes are known to control short-term gravel barrier dynamics and long-term barrier migration, a detailed quantification of overwash flow properties and induced bed-changes is crucial. Overwash hydrodynamics of the prototype gravel barrier focused on the flow velocity, depth and discharge over the barrier crest, and the overwash flow progression across and the infiltration through the barrier. During the BARDEX experiment, overwash peak depth (0.77 m), velocity (5 m s−1 ) and discharge (max. 6 m3 m−1 ) were high, especially considering the relatively modest wave energy (significant wave height = 0.8 m). Conversely to schemes found in the literature, average flow depth did not linearly decrease across the barrier; rather, it was characterised by a sudden decrease at the crest, a milder decrease at the barrier top and then propagation as a shallow water lens over the backbarrier. The barrier morphological evolution was analysed over a series of 15-min experimental runs and at the timescale of individual overwash events. Overall, the morphological variation did not result from an accumulation of many small consistently erosive or accretionary events, but rather the mean bed elevation change per event was quite large (10 mm) and the overall morphology change occurred due to a small imbalance in the number of erosive and accretionary events at each location. Two relationships between overwash hydrodynamic variables were deduced from results: (1) between overwash flow depth and velocity a power-type relation was obtained; and (2) a linear relation was observed between overwash flow depth and maximum overwash intrusion distance across the barrier top (i.e. overwash intrusion). Findings from this study are useful to enhance the knowledge of overwash processes and also have practical applications. On the one hand, results shown here can be use for the validation of overwash predictive models, and additionally, the simple empirical relations deduced from the dataset can be used by coastal managers to estimate overwash intrusion distance, which in turn can assist in the location of areas under risk of overwash and breaching.
- Downwearing rates on shore platforms of different calcareous lithotypesPublication . Moura, Delminda; Gabriel, Selma; Ramos-Pereira, Ana; Neves, Mário; Trindade, Jorge; Viegas, José; Veiga-Pires, C.; Ferreira, Óscar; Matias, Ana; Jacob, J.; Boski, T.; Santana, PauloVertical lowering (downwearing) of shore platform surfaces is a very important mechanism in their morphological evolution albeit much remains incompletely understood. The efficacy of mechanical and chemical weathering acting on a given substrate, together with erosional processes, influences downwearing rates. In order to determine the relationship between lithotypes and downwearing rates, data collected from a Transverse Micro-erosion Meter were obtained for shore platforms of three different calcareous lithotypes (biocalcarenite, calcarenite and carbonated siltstone) along the central Algarve coast (Southern Portugal). Downwearing rates ranged between 0.096 mm year−1 and 1.676 mm year−1 in biocalcarenite and weakly cemented calcarenite, respectively. In addition, physical properties of the rocks comprising the platforms were measured, including uniaxial compressive strength (as determined by the Point Load Test), porosity, and calcium carbonate content. The results show that downwearing depends primarily on the intrinsic properties of the substrate. Porosity, in particular, acts in two ways: (i) it tends to weaken the substrate; and, (ii) it controls the downward extent of the water percolation and therefore the depth of the weathering mantle subject to erosion by waves and currents.
- Dynamic allometry in coastal overwash morphologyPublication . Lazarus, Eli D.; Davenport, Kirstin L.; Matias, AnaAllometry refers to a physical principle in which geometric (and/or metabolic) characteristics of an object or organism are correlated to its size. Allometric scaling relationships typically manifest as power laws. In geomorphic contexts, scaling relationships are a quantitative signature of organization, structure, or regularity in a landscape, even if the mechanistic processes responsible for creating such a pattern are unclear. Despite the ubiquity and variety of scaling relationships in physical landscapes, the emergence and development of these relationships tend to be difficult to observe - either because the spatial and/or temporal scales over which they evolve are so great or because the conditions that drive them are so dangerous (e.g. an extreme hazard event). Here, we use a physical experiment to examine dynamic allometry in overwash morphology along a model coastal barrier. We document the emergence of a canonical scaling law for length versus area in overwash deposits (washover). Comparing the experimental features, formed during a single forcing event, to 5 decades of change in real washover morphology from the Ria Formosa barrier system, in southern Portugal, we find differences between patterns of morphometric change at the event scale versus longer timescales. Our results may help inform and test process-based coastal morphodynamic models, which typically use statistical distributions and scaling laws to underpin empirical or semi-empirical parameters at fundamental levels of model architecture. More broadly, this work dovetails with theory for landscape evolution more commonly associated with fluvial and alluvial terrain, offering new evidence from a coastal setting that a landscape may reflect characteristics associated with an equilibrium or steady-state condition even when features within that landscape do not.
- Estudo morfosedimentar da península de CacelaPublication . Matias, Ana; Dias, Alveirinho; Ferreira, ÓscarA Península de Cacela localiza-se no extremo oriental do sistema de ilhas barreira da Ria Formosa, caracterizado por possuir um carácter extremamente dinâmico, quer ao nível das movimentações sedimentares transversais, quer longilitorais. Devido à elevada vulnerabilidade em que o seu cordão dunar se encontrava foram realizados vários tipos de medidas de recuperação que incluem a alimentação artificial, a colocação de estacaria, a re-vegetação dunar e a colocação de passagens pedonais sobreelevadas. A presente dissertação visou por um lado a caracterização morfodinâmica da Península de Cacela e, por outro, a compreensão da evolução desta zona na sequência das intervenções, tentando encontrar formas de avaliar quantitativamente a sua eficácia. Para tal foi estabelecido um programa de monitorização que consistiu na realização mensal de perfis de praia emersa e na recolha de amostras de sedimentos de praia e de duna, embora com menor regularidade, e na realização ocasional de levantamentos topográficos em alguns locais da península. Foram ainda analisados dois anos de dados de agitação marítima, uma série de fotografias aéreas verticais (entre ~1940 e 1999) e a vulnerabilidade do cordão dunar através de uma checklist. A evolução recente da Península de Cacela (~1940 a 1999) caracterizou-se por uma substancial diminuição do cordão dunar, dado o significativo recuo da linha de costa, a migração para nascente da Barra do Lacém e o aumento das áreas de galgamento oceânico. Este processo conduziu a uma fragilização do cordão dunar desta península, tendo ocorrido ruptura total durante o inverno de 1995/96. No inverno seguinte (1996/97) as características desta península foram drasticamente alteradas pela implementação de um conjunto de medidas de recuperação dunar. A aplicação da checklist de vulnerabilidade dunar demonstrou uma melhoria das condições de praia e de duna devido às medidas de intervenção a que este troço costeiro foi sujeito. No entanto, a aplicação deste método a todos os corpos dunares da Ria Formosa revelou que, genericamente, os resultados são concordantes com as condições reais, mas existe necessidade de reformulação de certos parâmetros e índices. O material usado para a alimentação artificial das dunas da Península de Cacela possuía características granulométricas muito distintas das apresentadas pelas dunas naturais, tendo ocorrido aproximação granulométrica nos locais em que houve recuperação dunar por colocação de armadilhas de areia. Quanto à praia, verificou-se uma grande variabilidade longilitoral e temporal, já notória antes da realimentação. Esta heterogeneidade sedimentar pode constituir vi uma característica intrínseca deste troço costeiro, relacionada com uma fraca selectividade do agente de transporte, com a existência de variações longilitorais significativas da morfologia de praia emersa, ou com a existência de várias fontes sedimentares distintas. De um ponto de vista morfológico, a praia emersa apresentou variação entre dois estados distintos, o perfil de tempestade e o perfil de calmaria, desenvolvendo-se o primeiro numa escala de tempo relativamente curta, tendo-se observado que a recuperação para um perfil de calmaria foi relativamente lenta. Para uma análise quantitativa da evolução morfológica do perfil de praia foram estabelecidos cinco parâmetros, a que se designou por descritores (pendor da face, pendor do terraço, largura da berma, profundidade do runnel e volume de praia). O comportamento da praia, em termos de pendor de face, é relativamente coerente com a transição entre os dois estados da praia referidos, variação esta que se torna mais homogénea longitudinalmente no segundo ano analisado. Existe relativa concordância entre as variações volumétricas sazonais das zonas realimentada e natural, excepto no primeiro verão (1997), devido ao reajuste inicial da zona realimentada. Tendo sido efectuada a refracção dos dados de agitação para o litoral em estudo, foi efectuada a comparação entre a evolução dos vários descritores e as variações mensais e semanais da altura significativa da onda na rebentação (Hsb). Verificou-se que o pendor da face mostra dependência de Hsb média mensal na rebentação. A variação de volume da zona realimentada parece relacionar-se melhor com Hsb média semanal enquanto que a zona natural se relaciona com Hsb média mensal, o que pode ser um indicador de uma maior robustez da praia na zona onde se colocaram os dragados, ou resultar de uma fragilização da praia como consequência da remoção dos sedimentos da praia da zona dita natural, para colmatação dos galgamentos. Quanto ao depósito de dragados propriamente dito, ocorreu acentuada erosão (33% do total depositado) durante o período de monitorização. Estas perdas sedimentares foram mais acentuadas na zona adjacente à Barra do Lacém (45% da erosão registada) e nas zonas relativamente salientes do depósito, num processo que tende, provavelmente, para a linearização da frente da realimentação. Foram propostos métodos de avaliação da eficácia de alimentações artificiais e de estacaria de retenção de areia. A sua aplicação ao caso presente mostrou que o tempo de vida para o qual o índice de eficácia da realimentação é óptimo é de aproximadamente 14 anos. O método proposto de avaliação da estacaria mostrou que, globalmente, esta possui uma eficácia de cerca de 40%.