Percorrer por autor "Ferreira, Oscar"
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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.
- Assessing stakeholders’ risk perceptions in a vulnerable coastal tourism destination (Faro beach, Southern Portugal)Publication . Domingues, Rita B.; Costas, Susana; Jesus, Saúl; Ferreira, OscarEffective coastal management is essential in regions where tourism is a main economic activity. However, poor communication and disagreement between stakeholders hamper the way decisions are conveyed to residents and home/business owners, potentially affecting economic development. We analysed managers and scientists' views regarding risk perceptions of Faro Beach (Algarve) residents, contributing to the identification of differences and similarities towards a sustainable management. We used a qualitative content analysis of managers and scientists' discourses. Managers and scientists recognize that residents, particularly fishermen, are quite knowledgeable about the risks they face by living at the beach. However, scientists and managers believe that residents easily forget about the problems due to an optimism bias and positive previous experience with hazards, that never caused fatalities or serious consequences, leading to an underestimation of the severity of the risks. Managers think that residents are not concerned about the environmental problems of Faro Beach, and both scientists and managers see education as the best solution to increase risk perception and concern of residents. We suggest that truly collaborative approaches to coastal management should be promoted, including an active involvement of residents in the decision process, thus increasing their self-efficacy and behavioural control.
- Assessment of Overwash-induced flooding at two beaches along the Southwest Algarve, PortugalPublication . Kupfer, S.; Ferreira, Oscar; Costas, S.At the Algarve south coast overwash-induced floods are a frequent and destructive phenomenon. In this study return periods for overwash potentials are estimated for two beaches located at the southwest coast of the Algarve (Carvoeiro and Salema) based on runup calculations for the period 1995-2017 after applying two well validated empirical formulations. Results show that overwash potentials are high even for small return periods. Additionally, the suitability of two different indicators (overwash potential and overwash depth) has been tested to represent the flood extent. Results suggest that the flood extent derived from the overwash depth presents several limitations and cannot realistically represent observations, while the flood extent given by the overwash potential (using a simple bathtub approach) fairly represents the overwash-induced flood, even though it can over/underestimate the flood extent for gentle/steep inland slopes. Flood extents derived from the overwash potential, for return periods of 10- and 100-year, show that occupied areas are potentially flooded for both return periods. It is therefore necessary to define appropriate adaptation measures for both beaches, preferably based on detailed risk assessment.
- Beach morphodynamic impact on a macrobenthic community along a subtidal depth gradientPublication . Dolbeth, M.; Ferreira, Oscar; Teixeira, H.; Marques, J. C.; Dias, J.A.; Pardal, M. A.The subtidal macrobenthic community of a temperate beach in southern Portugal was studied along a depth gradient (1.3 to 32 m deep), which was long enough to comprise both highly hydrodynamic and calmer areas, to assess the influence of the spatial and temporal differences in hydrodynamic impact at the seafloor on the organization of a macrobenthic community. These differences were assessed by studying the variations in wave climate, depth of closure and extension of the mixed profile. A spatial zonation was detected from highly hydrodynamic shallow depths, 7.2 m deep shorewards, to the calmer deeper areas, from 8.4 m seawards. Accordingly, in the shallowest depths, species richness and densities were lower, with the inhabiting species, mainly crustaceans and surf clams, adapted to the environmental severity. Both species richness and densities increased along the depth gradient, and the community became dominated by polychaetes, nematodes and nemerteans. Seawards, within the relict sediments (deeper than 25 m), species richness and abundance decreased again. The community patterns also changed in response to the occurrence of strongly hydrodynamic episodes (such as storms), which had a higher impact than the seasonality. It was concluded that harsh physical environmental conditions reduce species richness, both spatially and temporally. With respect to density, other parameters related to life cycle characteristics, recruitment success and biotic interactions may also have some impact.
- 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.
- 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.
- Como é que os habitantes da Praia de Faro olham para os riscos costeiros?Publication . Domingues, Rita; Santos, Márcio C.; Jesus, Saúl; Ferreira, OscarFaro Beach is a vulnerable and heavily urbanized settlement, exposed to beach erosion, overwash and other hazards. However, residents seem to feel safe living there and have no intentions of ever leaving the beach. We developed questionnaires and went knocking on doors, asking how residents feel about their safety at the beach. We realised that fishermen and their families possess significant knowledge on coastal hazards that derive mainly from life experience. Their risk perception is not as low as we thought; however, residents believe hazards are not that dangerous and they will probably happen in the future, but not now. This optimism bias and psychological distance hinders their preparedness efforts towards hazards.
- Early Warning System development: Quarteira and Praia de FaroPublication . Garzon, Juan L.; Zozimo, Catarina; Ferreira, Andreia M. Marques; Ferreira, Oscar; Fortes, Conceição Juana; Reis, Maria TeresaMany coastal zones worldwide are heavily populated and host very important socio-economic sectors. Portugal is a good example of countries whose economy is highly dependent on tourism activities, especially those sea-related activities. The two sites selected in this project (Quarteira and Faro) receive thousands of national and international visitors annually, not only during the summertime but also in the rest of the seasons because of the favorable weather conditions. However, these sites have been acknowledged as coastal risk hotspots due to their exposure to wave-induced flooding and erosion. Under this threat, the implementation of effective disaster risk reduction (DRR) plans is vital for minimizing damages in occupied areas. In this regard, Early Warning Systems (EWSs) play an important role in allowing for preparedness, namely, timely site evacuation or effective intervention prior to the approaching storm. The successful implementation of EWSs is one of the most cost-effective and efficient measures for disaster risk reduction and the saving of lives. EWSs can rely on complex tools such as process-based models to simulate coastal hazards namely erosion and flooding. However, they are normally highly time-consuming and this aspect might represent a major limitation for operational systems. Conversely, Bayesian Networks (BNs) can provide risk probabilities instantly after being trained and they have been successfully used to make predictions of storm impacts in several coastal applications. The main disadvantage of Bayesian Networks is that they are data-intensive, requiring large input information in order to derive the probabilistic relationships used in their predictions. Under the lack of field observations, process-based models can be used to generate this required information. Once trained, the BN can be used as a surrogate for a process-based model in an EWS.
- Estimating the optimum size of a tidal array at a multi-inlet system considering environmental and performance constraintsPublication . González-Gorbeña Eisenmann, Eduardo; Pacheco, André; Plomaritis, Theocharis; Ferreira, Oscar; Sequeira, ClaudiaThis paper investigates the optimum tidal energy converter array density at a tidal inlet by applying surrogate-based optimisation. The SBO procedure comprises problem formulation, design of experiments, numerical simulations, surrogate model construction and constrained optimisation. This study presents an example for the Faro-Olhão Inlet in the Ria Formosa (Portugal), a potential site for tidal in-stream energy extraction. A 35 kW Evopod™ floating tidal energy converter from Oceanflow Energy Ltd. has been used for array size calculations considering two design variables: (1) number of array rows, and (2) number of tidal energy converter per row. Arrays up to 13 rows with 6–11 tidal energy converters each are studied to assess their impacts on array performance, inlets discharges and bathymetry changes. The analysis identified the positive/negative feedbacks between the two design variables in real case complex flow fields under variable bathymetry and channel morphology. The non-uniformity of tidal currents along the array region causes the variability of the resource in each row, as well as makes it difficult to predict the resultant array configuration interactions. Four different multi-objective optimisation models are formulated subject to a set of performance and environmental constraints. Results from the optimisation models imply that the largest array size that meets the environmental constraints is made of 5 rows with 6 tidal energy converter each and an overall capacity factor of 11.6% resulting in an energy production of 1.01 GWh year−1. On the other hand, a higher energy production (1.20 GWh year−1) is achieved by an optimum array configuration, made of 3 rows with 10 tidal energy converters per row, which maximises power output satisfying environmental and performance restrictions. This optimal configuration permits a good level of energy extraction while having a reduced effect on the hydrodynamic functioning of the multi-inlet system. These results prove the suitability and the potential wide use of the surrogate-based optimisation method to define array characteristics that enhance power production and at the same time respect the environmental surrounding conditions.
- Exploring foredune growth capacity in a coarse sandy beachPublication . Costas, Susana; Bon de Sousa, Luísa; Kombiadou, Katerina; Ferreira, Oscar; Plomaritis, Theocharis A.Dunes are key elements of coastal landscapes in almost every latitude. They host high levels of biodiversity and provide important benefits to society; e.g. protection against floods and erosion, or recreation. Coastal dune growth is constrained by intrinsic factors, which are critical when managing dune systems or choosing coastal dune restoration as an alternative green solution for coastal protection. Here, the evolution of a beach-dune system, characterized by a reflective coarse sandy beach and low dunes, is explored to identify the favourable and optimal conditions for dune growth in these settings. Dune growth capacity is evaluated by analysing the topographical changes observed along a coastal dune over two different temporal scales (interannual and event scale) and comparing the observations with theoretical approximations of sediment transport potentials. Observations and predictions over interannual scale document that (1) temporal variability in external conditions (wind regime) and spatial variability of estimated wind fetch length, alone, fail to explain alongshore dune growth patterns and (2) optimal conditions for dune growth occur when storms (strong winds) impact the study area, jointly with low runup levels, at zones of shoreline progradation and absence of direct human influence. Conversely, lowest values of dune accumulation are associated with areas where shoreline retreat was documented. Observations from event timescales suggest that sediment transport potential can be reached over zones with no significant signs of beach erosion, if runup levels remain low and the event duration is shorter than the time scale of sand surface depletion within the upper beach.