Artigos de Revista
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Dynamics of CO2, CH4, and N2O in Ria Formosa coastal lagoon (southwestern Iberia) and export to the Gulf of Cadiz
A first characterization of greenhouse gases had been carried out to study their role and impact in a productive transitional coastal system of the southern Portugal
Ano: 2024
Número Páginas:
17p..
Autor(es): Sierra, A.; Correia, C.; Ortega, T.; Forja, J.; Rodrigues, M.; Cravo, A.
Revista: Science of the Total Environment
Editor: Elsevier
Volume:
(906)167094.
Keywords: Coastal lagoon; Ria Formosa; Gas mass transport; Water - atmosphere fluxes; Greenhouse gases
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2DH modelling and mapping of surfbeat-driven flooding in the shadow of a jettied tidal inlet
Near estuaries and harbours, submerged shoals and defence structures impact the exposure to overtopping. These features may be accounted for in two-dimensional horizontal (2DH) numerical models, either based on phase resolving or phase-average solvers for wave propagation. In between, surfbeat solvers, such as in XBeach, combine an affordable computational cost with the ability to generate and propagate the longer infragravity (IG) waves. However, surfzone wave characteristics and the overtopping exposure modelled with XBeach are sensi tive to settings such as the shape of the forcing wave spectra and the numerical scheme for wave propagation. The present paper explores this sensitivity and assesses the performance of different inundation models built with the 2DH surfbeat solver of XBeach. These models were forced with downscaled water levels and directional wave spectra and the results fuelled a discussion bounded by data collected downdrift of the entrance to the harbour of Figueira da Foz (Portugal). The original second-order upwind scheme, which propagates short-waves with a lower numerical diffusion improved the model performance in terms of long-wave height, and an unconventional breaking criterion better represented the cross-shore distribution of short-wave height near the shore. A cali brated model was validated through the hindcast of an overtopping event observed under moderate swell forcing, and was used to map the overtopping exposure during a hypothetical combination of an energetic swell with a water level having a return period of ~70 years. Compared to the default wave spectra shape and model settings, using an appropriate representation of the short-wave directional spectrum at the open boundary was necessary to reproduce the observed overtopping extent. Refining the cross-shore resolution of the model helped to better represent the observed inundation extents, as also did the reduction of the friction coefficient. Addi tional phase-resolving simulations in 1DH overestimated IG wave energy and produced higher and more frequent overtopping discharges. The differences with the calibrated 2DH surfbeat model increased with the proximity of the inlet and with short-wave height and angle of incidence. Overall, required calibration steps were provided. They aim at making 2DH XBeach surfbeat a credible tool for 1) predicting short and IG wave characteristics up to the shoreline, as well as for 2) providing first estimates of exposure to overtopping in areas with shallow and alongshore-irregular morphologies.
Ano: 2023
Número Páginas:
1-21pp.
Autor(es): Nahon, A.; Fortunato, A. B.; Oliveira , F.; Azevedo, A.; Henriques, M.; Silva, P. A.; Baptista, P.; Freire, P.
Revista: Coastal Engineering
Editor: Elsevier B.V.
Volume:
184.
Keywords: XBeach; Infragravity waves; Ebb-tidal delta; Intermediate beach; Overtopping
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Effects of droughts, sea level rise, and increase in outfall discharges on phytoplankton in a temperate estuary (Tagus Estuary, Portugal)
The efects of climate change on the estuarine environment are not fully understood. In temperate regions, droughts are expected to increase in frequency and severity, due to lower precipitation, and the mean sea level is expected to rise. This study aimed to assess how the estuarine environment will be afected by river fow
Ano: 2023
Número Páginas:
111p.
Autor(es): Cereja, R.; Brotas, V.; Brito, A.; Rodrigues, M.
Revista: Regional Environmental Change
Editor: Springer
Volume:
Volume 23.
Keywords: Modeling; Climate change; Phytoplankton; River discharges; Sea level rise; Tagus Estuary
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The complexity of the coastal zone: definition of typologies in Portugal as a contribution to coastal disaster risk reduction and management
Mainland Portugal presents an extensive, diversified and complex coastal zone. This diversity gives rise to diverse geomorphologic features which support different densities of human occupancy and a range of land uses and activities. In this sense, the coastal zone becomes an area of great national strategic value, but has also into a multi-hazard zone. To understand this complexity, two statistical techniques, namely Cluster Analysis and Principal Component Analysis, were used to identify and differentiate, between the different coastal typologies, based on a set of variables that express the territorial complexity and the occurrences and impacts of coastal flooding. The chosen methodology enabled a diverse set of coastal typologies to be identified, which contributes towards differentiating local specific characteristics. The holistic and differentiating nature of the applied methodology and the results obtained allows it to contribute to the definition of mitigation strategies and the implementation of adaptation measures. The results enable us to define a set of typologies associated with Coastal Disaster Risk Reduction and Management which are an important contribution to comprehensive coastal flood risk assessment and management.
Ano: 2023
Número Páginas:
103556.
Autor(es): Barros, J.; Santos, P.; Tavares, A.; Freire, P.; Fortunato, A. B.; Rilo, Ana; Oliveira , F.
Revista: International Journal of Disaster Risk Reduction
Editor: Elsevier
Volume:
Volume 86.
Keywords: Principal component analysis; Cluster analysi; Disaster risk reduction; Risk management; Portugal; Coastal zone; Coastal typologies
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Modeling LoRa communications in estuaries for IoT environmental monitoring systems
Low-power wide-area networks (LPWANs) are extending beyond the conventional terrestrial domain.Coastal zones, rivers, and wetlands, among others, are nowa days common deployment settings for Internet-of-Things nodes where communication technologies such as Long Range (LoRa) are becoming popular. In this article, we inves tigate large-scale fading dynamics of LoRa line-of-sight (LoS) links deployed over an estuary with characteristic intertidal zones, considering both shore-to-shore (S2S) and shore-to vessel (S2V) communications. We propose a novel method ology for path-loss prediction which captures: 1) spatial;2) temporal; and 3) physical features of the RF signal interaction with the environmental dynamics, integrating those features into the two-ray propagation model. To this purpose, we resort to precise hydrodynamic modeling of the estuary, including the specific terrain profile (bathymetry) at the reflection point. These aspects are key to accounting for a reflecting surface of varying altitude and permittivity as a function of the tide. Experimental measurements using LoRa devices operating in the 868-MHz band show major trends in the received signal power in agreement with the methodology
Ano: 2022
Número Páginas:
21312-21325pp.
Autor(es): Gaitán, M.; d'Orey, P.; Cecílio, J.; Rodrigues, M.; Santos, P; Pinto, L.; Oliveira, A.; Casimiro, A.; Almeida, L.
Revista: IEEE Sensors Journal
Editor: IEEE
Volume:
Volume 22, Issue 21.
Keywords: two-ray mode; tidal fading; radio-frequency (RF) propagation; path loss,; overwater communications; Long Range (LoRa); Intertidal zone
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Modelling the contribution of wind waves to Cap Ferret's updrift erosion
Wind waves breaking at an angle with the shoreline force the drifting of littoral sediments, which is known forcontributing to the formation and growth of barrier spits. Intriguingly, increased rates of longshore wave powerhave also been associated with the erosion of some barrier spits on the updrift margin of tidal inlets. Therefore, a numerical experiment was designed and is presented here, which investigates the possible links between thelongshore wave power and the shortening of these elongated coastal barriers. Based on a process-based model, the experiment provides new insights into the forces at play in the redistribution of sediments between a sandspit and its adjacent inlet, respectively the Cap Ferret and the Bay of Arcachon
Ano: 2022
Número Páginas:
104063.
Autor(es): Nahon, A.; Idier, D; Bertin, X.; Guérin, T.; Marieu, V.; Sénéchal, N.; Mugica, J.
Revista: Coastal Engineering
Editor: Elsevier B.V.
Volume:
Volume 172.
Keywords: SCHISM; NAO; Wave power; Sediment transport; Tidal inlet; Sandspit
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One step from the deep ocean: Linking research and governance for the Tagus river estuary and the Lisbon canyon system
Ministry of the Sea promoted an expert conference to discuss the currentstate of the Tagus river estuary and adjacent oceanic areas and to promotefuture action. The Tagus river estuary shapes the Lisbon MetropolitanArea, bordering 11 water-facing municipalities across 320 km2(among the largest in Europe and critically positioned along the North-South bird migration corridor of the East Atlantic [1]). It communicateswith the deep North Atlantic through the Tagus submarine prodelta andthe Lisbon/Cascais/Setúbal canyon system (Fig. 1). This proximity allowsinteraction of water masses and biological communities betweenthe estuary and the deep ocean and deserves scientific attention.The conference integrated perspectives on current threats, aftermillennia of human occupation and decades of local efforts to improveenvironmental status and contributed towards an action plan to maintainor improve ecosystem services for this densely populated area,following an ecosystem stewardship framework [2].
Ano: 2022
Número Páginas:
105224.
Autor(es): Stratoudakis, Y.; Caetano, M.; Afonso, C.; Bartilloti, C.; Santos, A.; Terrinha, P.; Figueiredo, I.; Miranda, M.; Costa, J. L.; Caçador, M.; Fonseca, V.; Chainho, P.; Melo , Ricardo .; Quintella, B.;
Revista: Marine Policy
Editor: Elsevier
Volume:
Vol. 144 (2022).
Keywords: Integrated ecosystem stewardship; Connectivity; Submarine prodelta and canyon; Tagus urban estuary
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Wave-current interactions at the Tagus Estuary Mouth (Portugal) under storm wave conditions
This study investigates interactions between waves, water levels and currents at the mouth of the second largest estuary in Europe (the Tagus Estuary, Portugal) under storm waves, combining field observations and a threedimensional fully coupled wave-current modelling system. Tidal-induced water depth variations substantially modulate waves over the ebb shoal. During energetic conditions, low tide levels promote depth-limited wave breaking and energy transfer towards higher harmonics (triad interactions), which reduces wave heights and periods. Furthermore, for a given water level, tidal currents also influence wave propagation and drive strong modulations over shallow regions characterized by cross-channel current gradients. Flood currents change the mean wave direction by about 10
Ano: 2022
Número Páginas:
102035.
Autor(es): Mengual , B.; Bertin, X.; Place, F.; Pezerat, M.; Coulombier, T.; Mendes, D.; Fortunato, A. B.
Revista: Ocean Modelling
Editor: Elsevier
Volume:
Vol. 175 (não tem número).
Keywords: The Tagus Estuary; Large estuary mouth; Storm waves; Wave-current interactions
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A coastal flooding database from 1980 to 2018 for the continental Portuguese coastal zone
Continental Portugal presents an extensive and diversified coastal zone which concentrates the main public andprivate infrastructures of the different economic sectors, as well as the main critical infrastructures. This area isalso characterized by a high population density, being a differentiated territory in geophysical, biological andlandscape terms. The wave regime is highly energetic, and storms are frequent. In the last decades, the coast ofcontinental Portugal has been affected numerous times by overtopping and coastal flooding processes. Identifyingthe critical coastal typologies affected by flooding can contribute to a comprehensive flood risk managementframework for the Portuguese coastal zones. Hence, a historical database of coastal flooding occurrenceswas created for the period 1980
Ano: 2021
Número Páginas:
1-17pp.
Autor(es): Tavares, A.; Barros, J.; Freire, P.; Santos, P.; Perdiz, L.; Fortunato, A. B.
Revista: Applied Geography
Editor: Elsevier
Volume:
Volume 135, 2021 102534.
Keywords: Occurrences; Impacts; Database; Coastal flooding; Coastal zone
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Comprehensive bathymetry and intertidal topography of the Amazon estuary
The characterization of estuarine hydrodynamics primarily depends on knowledge of the bathymetryand topography. Here, we present the first comprehensive, high-resolution dataset of the topography andbathymetry of the Amazon River estuary, the world
Ano: 2021
Número Páginas:
2275-2291.
Autor(es): Andrade, A.; Durand, F.; Moreira, D.; Azevedo, A.; Santos, V. F.; Funi, C.; Laraque, A.
Revista: Earth System Science Data
Editor: Earth System Science Data
Volume:
13.
Keywords: estuary; Amazon
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Comunicações
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Influence of non-linear waves and undertow in sandbar development
As waves propagate from deep into shallow waters, they begin to interact with the sea floor and undergo through several changes due to non-linear effects. These interactions cause the waves to transform and become non-linear as they decelerate and finally break. These local nonlinearities are reflected on the near-bed oscillatory flow and are inextricably linked to sediment transport, causing erosion-accretion patterns and bar migration. In this work the ability of a practical transport model that includes the effects of velocity and acceleration skewness in the time-varying bed shear stress (Abreu et al., 2011) is assessed to predict sediment transport rates under oscillatory flows and currents. The results are compared with two different data sets obtained under sheet flow conditions, showing a good agreement with the measurements. Moreover, its performance to the undertow and to non-linear characteristics is further assessed. The practical sediment transport model is coupled to a simple bed-evolution model, enabling to evidence the relative strength of mechanisms associated with the wave and current induced sand transports. The results show that the formation of the bar and its migration is affected by a new term introduced in the bed shear stress predictor. This time-varying term accounts for the shape of the wave and is described through two non-linear parameters recently proposed in Abreu et al. (2010).This work provides further insights in the correct prediction of sediment transport modeling and sandbar developments, due to the combined influence of non-linear waves with undertow currents.
Ano: 2012
Número Páginas:
1-14pp.
Autor(es): Abreu, T.; Sancho, F. E.; Silva, P. A.
Keywords: Sandbar; Undertow; Asymmetry; Skewness; Non-linear waves
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Influence of the wave regime in coastal sediment budget: present and future scenarios
The wave regime has a strong influence on the sediment transport in coastal systems. Modifications in wave regimeinduced by climate changes can influence the sediment dynamics of those coastal systems. To access wave regimechanges it is crucial to analyse the future modifications in the wave height, period and direction. This work aims toanalyse the influence of a future wave regime in the sediment budget of a coastal lagoon inlet and at the nearshoreadjacent coast. To achieve this goal a morphodynamic modelling system was used, forced by present and futurewaves, corresponding to a typical year of present and future wave climates. A methodology to determine a typicalyear of each climate was developed based on the determination of correlation coefficients between each climate andcorresponding year data. The comparison between present and future wave climates evidences that wave period andheight are in general similar for both climates, and confirms the anticlockwise rotation of waves in the future. Themorphodynamic simulations revealed analogous results for both wave climates, resulting in similar patterns for theresidual sediment fluxes, but slightly more intense in the present. The consequent bathymetric changes show that thedeposition trend presently observed offshore the inlet tends to increase for future waves climate. The transportbudgets were also analysed for both wave regimes, evidencing that the alongshore transport slightly decreases (~1%)for future waves.
Ano: 2012
Número Páginas:
1-12pp.
Autor(es): Plecha, S.; Lopes, C. L.; Bruneau, N.; Ribeiro, N. A.; Silva, P. A.; Fortunato, A. B.; Dias, J. M.
Keywords: Ria de aveiro; Morphodynamics; Climate change; Wave climate
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Interactions vagues-courants dans une embouchure tidale dominée par la houle
Les embouchures tidales permettent les échanges d
Ano: 2012
Número Páginas:
41-50pp.
Autor(es): Dodet, G.; Bertin, X.; Bruneau, N.; Fortunato, A. B.; Nahon, A.; Taborda, R.
Keywords: Blocage des vagues; Modélisation numérique; Hydrodynamique côtière
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Modelação da inundação costeira na Ria de Aveiro
As inundações costeiras constituem uma preocupação crescente para as autoridades, o que temmotivado um esforço para simular estes acontecimentos extremos. Em suporte à futuraaplicação da nova directiva de avaliação e gestão dos riscos de inundações (2007/60/CE), foramdesenvolvidos mapas de inundação para a Ria de Aveiro. A Ria de Aveiro é uma laguna extensa(cerca de 45 por 10 km) e pouco profunda (profundidade média de 1 m), com pequenasafluências fluviais. No entanto, está exposta à agitação marítima intensa proveniente doAtlântico, assim como a sobre-elevações de origem meteorológica (storm surges), que podemexceder 1 m na embocadura. O presente artigo descreve a abordagem seguida nodesenvolvimento dos mapas de inundação.A primeira parte do artigo descreve a metodologia adoptada, incluindo as hipóteses de base e asua validação. Para definir as condições de fronteira para forçar um modelo de circulação, foidesenvolvido um novo método que permite determinar os níveis máximos e as séries temporaisassociadas para diferentes períodos de retorno, baseado na análise estatística de sériestemporais longas em estações costeiras. O método considera o efeito das marés, das stormsurges e do ciclo de 19 anos de variabilidade das marés, tendo em conta pequenas correlaçõesentre storm surges e marés. Os níveis extremos obtidos com este novo método convergem paraos 20 anos de dados disponíveis em Aveiro e são semelhantes aos produzidos por abordagensconvencionais. Relativamente a estas abordagens, o novo método tem a vantagem de produzirnão apenas os níveis extremos, mas também as séries temporais que os incluem, e que sãonecessárias para forçar o modelo de circulação.A segunda parte do artigo descreve a implementação e validação do modelo de circulação(SELFE) para a simulação da inundação na Ria de Aveiro. Salienta-se a construção semiautomáticade uma malha de elementos finitos que permite simular de forma eficiente umdomínio muito extenso e com a resolução adequada nos canais estreitos que controlam ahidrodinâmica da laguna. Os coeficientes de fricção nas zonas inundáveis são calculados a partirda ocupação dos solos definida na base de dados Corine Land Cover. A validação do modelo decirculação mostra uma precisão comparável ou superior a simulações anteriores para estesistema.Finalmente, apresentam-se os mapas de inundação para vários períodos de retorno, ecomparam-se com outros mapas desenvolvidos com base em abordagens alternativas.
Ano: 2012
Número Páginas:
1-15pp.
Autor(es): Fortunato, A. B.; Rodrigues, M.; Dias, J. M.; Oliveira, A.
Keywords: Inundação; Malhas não estruturadas; Métodos estatísticos; Modelação numérica
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Modelação numérica da erosão de dunas durante tempestades
Aplicaram-se os modelos matemáticos de morfodinâmica XBeach, Litprof e Duner para avaliar a variaçãotemporal da resposta de um perfil de praia à ação erosiva de uma tempestade marítima. Testaram-se os modelospara um caso de erosão de duna em modelo laboratorial de grande escala. A avaliação do desempenho foi feitacom base na análise da evolução morfológica e em indicadores de impacto e de erro. Os três modelosreproduziram a erosão da duna, mas foi o XBeach que apresentou o melhor desempenho. O modelo Dunerrevelou ser um instrumento simples e eficiente na impossibilidade aplicar modelos numéricos mais complexos
Ano: 2012
Número Páginas:
10pp.
Autor(es): Oliveira, F. S. B. F.
Keywords: Duner; Litprof; Xbeach; Praia; Morfodinâmica
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Modelling horizontalvelocities within the wave bottom boundary layer
As waves travel and shoal towards a beach, their surface elevation becomes peaky (sharp crests) and asymmetric relative to the vertical, differing from the sinusoidal profile of linear waves. Below the surface, the passage of the progressive waves induces fluid velocities, showing similar (time) asymmetries. These nonlinearities are inextricably linked to sediment transport, but the processes involved are not well understood. This work analyses the data collected during a recent experimental project under skewed oscillatory flows. It validates a simple method based on the defect law to reproduce the horizontal velocities within the wave bottom boundary layer. Results indicate a good agreement between the measured and modeled velocities using this methodology.
Ano: 2012
Número Páginas:
1-8 pp.
Autor(es): Abreu, T.; Silva, P. A.; Sancho, F. E.; Michallet, H.; Vasconcelos, L.
Keywords: Sheet-flow.; Defect law; Horizontal velocities; Oscillatory flows
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Morphodynamique d
La présente étude examine le comportement morphologique d
Ano: 2012
Autor(es): Nahon, A.; Freire, P.; Pires, A. R.; Dodet, G.; Bertin, X.; Freitas, M. C.; Fortunato, A. B.; Andrade, C.
Keywords: Morphodynamique; Fermeture naturelle; Dérive littorale; Embouchure tidale
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OIL SPILL DETECTION AND MODELLING: PRELIMINARY RESULTS FOR THE CERCAL ACCIDENT
Oil spill research has significantly increased mainly asa result of the severe consequences experienced fromindustry accidents. Oil spill models are currently ableto simulate the processes that determine the fate of oilslicks, playing an important role in disaster prevention,control and mitigation, generating valuable informationfor decision makers and the population in general. Onthe other hand, satellite Synthetic Aperture Radar (SAR)imagery has demonstrated significant potential in accidentaloil spill detection, when they are accurately differentiatedfrom look-alikes. The combination of bothtools can lead to breakthroughs, particularly in the developmentof Early Warning Systems (EWS). This paperpresents a hindcast simulation of the oil slick resultingfrom the Motor Tanker (MT) Cercal oil spill, listedby the Portuguese Navy as one of the major oil spills inthe Portuguese Atlantic Coast. The accident took placenearby Leix
Ano: 2012
Número Páginas:
5p.
Autor(es): Costa, R.; Azevedo, A.; Silva, J. C.; Oliveira, A.
Revista: European Spatial Agency (ESA) Special Publication
Editor: European Spatial Agency (ESA)
Keywords: Isw; Drp; Ews; K-means; Sar; Eulerian-lagrangian model; Cercal; Oil spill
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Reabilitação e protecção da praia de Colwyn Bay, Reino Unido
O artigo descreve um estudo de dinâmica costeira que teve como objectivo a reabilitação e protecçãoda praia de Colwyn Bay, em estado de avançada erosão e degradação das suas funções recreativa ede protecção costeira. O estudo foi desenvolvido em duas partes: a caracterização da dinâmica dapraia e o teste de soluções alternativas. Na primeira parte avaliou-se: a evolução tridimensional do topoe face de praia; a composição sedimentológica recente da mesma zona; a hidrodinâmica da praia, combase numa série de agitação marítima e numa série de nível do mar; e a distribuição do transportelongitudinal na zona activa submersa. Tendo em vista soluções alternativas baseadas numa estratégiade alimentação artificial, na segunda parte do estudo definiu-se o perfil de enchimento e testaram-sesoluções de longo prazo, algumas com estruturas de retenção/protecção (esporões, esporões em Y equebra-mares destacados). Definiu-se o perfil de enchimento com base: no método 2S-EBP, para aface e zona submersa activa; e no teste ao recuo de praia sob tempestade (modelaçãomorfodinâmica), para a berma. O teste de soluções alternativas realizou-se com dois modelos deevolução de linha de costa. Na fase inicial, testaram-se duas soluções de alimentação sem estruturasde protecção: 3.3 milhões de m3 de areia com D50=0.25 mm e 2.2 milhões de m3 de areia comD50=0.45 mm. Posteriormente, testou-se o efeito das estruturas na retenção do enchimento. Osresultados, avaliados qualitativamente e quantitativamente, indicaram que as melhores soluções deretenção são baseadas em estruturas normais à praia.
Ano: 2012
Número Páginas:
1-19pp.
Autor(es): Oliveira, F. S. B. F.; Freire, P.; Sancho, F. E.; Clímaco, M.; Vicente, C.
Keywords: Evolução da linha de costa; Modelação costeira; Alimentação artificial; Protecção costeira; Erosão costeira
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Sand transport in the swash zone in low-energy wave conditions
The interaction between waves and morphological changes at the beach face under low wave-energy conditions is examined from data obtained during a field survey at Praia de Faro (Algarve, Portugal). This work describes and analyses measurements of swash velocities acquired with current-meters, water surface elevation obtained with pressure transducers and topographic surveys undertaken during the field campaign. Estimations of sand transport rates are calculated considering different empirical formulations, and the results are then compared against the transport rates deduced from topographic measurements. A representative swash velocity time series based on the non-linear formulation of Abreu et al. (2010) is derived to study the dependence of the bed shear-stress skewness on the tidal phase and how this can affect sediment transport in the swash zone.
Ano: 2012
Número Páginas:
1-13pp.
Autor(es): Silva, C.; Abreu, T.; Sancho, F. E.; Ferreira, Ó.; Bezerra, M.; Ferreira, L.; Rocha, M.; Fortes, C. J. E. M.
Keywords: Praia de faro; Sediment transport; Swash; Field measurements
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Livros
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MEC2011 - Conferência sobre Morfodinâmica Estuarina e Costeira
N/A
Ano: 2011
Autor(es): Fortunato, A. B.; Freire, P.; Oliveira, A.
Editor: Laboratório Nacional de Engenharia Civil
Volume:
CD Room.
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Capítulos de Livros
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Evaluating the geomorphologic stability of an estuarine sandy beach. Integrated Coastal Zone Management
The hydrodynamics and sediment dynamics of a low energy estuarine beach was analysed. The beach is subjected to local wind waves generated in an area of restricted fetch, wake waves generated by catamarans and a semi diurnal meso-tidal regime. Only storm events of short duration modify the beach profile, which, once the normal hydrodynamic conditions are restored, naturally recovers its initial shape. The beach is characterised by having a steep upper slope until mean sea level, followed, seaward, by a low gradient terrace, and a bimodal sediment distribution. To investigate the hydro sedimentologic beach behaviour, wind, topo-hydrographic and sedimentologic data were used as input and validation of process based numerical modelling. Wave generation and transformation in an area of restricted fetch, nearshore circulation, sediment transport and morphological evolution were simulated for average annual conditions and storm conditions. The statistical analysis of a six-year wind data series allowed to derive the average wind regime, based on which, the average annual wave regime and the average annual longshore sediment budget, 14.5x103 m3year-1, were calculated. The contribution of the individual components of the representative wave regime, discretised by directional sector and height class of incidence, was evaluated as well as the spatial distribution of the longshore sediment transport in the active part of the beach profile. The characteristics of the wave groups generated by the passage of catamarans at different speeds were estimated and their action on the beach morphology was simulated. Although when the catamarans travel at 20 knots speed the average annual wake wave energy dissipated at the beach is 2.5 times higher than the average annual wind wave energy, the erosion effect on the beach profile is still not relevant for the present traffic. In opposition, short duration storm events generate the formation of an erosion scarp at the upper part of the beach face. The numerical modelling of this phenomenon allowed to acknowledge on the protective effect that the low gradient terrace has on the beach face.
Ano: 2009
Número Páginas:
pp. 35-49.
Autor(es): Oliveira, F. S. B. F.; Vargas, C.
Editor: Wiley-Blackwell Publishing
Volume:
Integrated Coastal Zone Management.
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Teses de Doutoramento
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Three-dimensional modelling of cohesive sediment transport in estuarine environments
N/A
Ano: 1995
Autor(es): Costa, R.
Editor: ******
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A Two-Dimensional Hydrodynamic Model Using a Finite-Volume Approach
A two-dimensional model of wind-driven circulation in a closed basin was developed using a finite-volume technique for generalized curvilinear grids and applying some of the recent developments in hydrodynamic modeling. The terms in the Navier¬Stokes equations were treated separately according to the fractional step method and the propagation step, including the continuity equation and the pressure and stress terms in the momentum equations, was solved using a conjugate gradient method.The model was then applied to a number of test cases to examine the feasibility of the approach used by comparing with results obtained with the two-dimensional version of the three-dimensional model CH3D. These included a square basin with constant slope and with a V-shaped bottom and Lake Okeechobee, in South Florida. To evaluate the long-term numerical stability of the model, a ten-day model simu¬lation with varying wind was also run for Lake Okeechobee.
Ano: 1989
Autor(es): Capitao, J.
Editor: ******
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Flow-Fine Sediment Hysteresis in Sediment-Stratified Coastal Waters
An examination of the causes for generation and dynamics of turbidity maxima in estuaries reveals the critical role of sediment tidal pumping phenomenon and, to a lesser extent, of the well-known effect of residual gravitational circulation due to salt water penetration. Both phenomena depend on the vertical sediment concentration profile and, consequently, on the magnitude of the vertical mass transport fluxes. Where high concentration suspensions occur regularly, the erosion/deposition fluxes can be drastically modified by sediment stratification, consequently influencing sus¬pended sediment response to currents and wave action. This influence is inherent in flow-sediment hysteresis, which therefore reflects the role of vertical mass transport in the estuarine and coastal suspended fine sediment regime.A vertical transport numerical model was used to investigate the influence of several key parameters describing sediment settling, bed properties and stabilized diffusion on the concentration profile. The model was also applied to simulate the influence of the same parameters on the time-lagged sediment response to flow variations, reflected in the characteristics of flow-sediment hysteresis loops.Field data obtained in Hangzhou Bay (People´s Republic of China), a high concentration environment, showed typical features of flow-sediment hysteresis and confirmed the importance of the vertical mass fluxes in contributing to sediment transport in the bay. A qualitative simulation provided by the numerical model, using settling parameters corresponding to local sediment, while confirming the importance of the hysteresis phenomenon, also revealed the critical need to use algorithms describing adequately stabilized diffusion and bed fluxes.Additional evidence of hysteresis was obtained through analysis of microscale variables, such as the Reynolds stresses and the variances of the velocity components resulting from combined effects of wave action and turbulence. Spectral analysis of the measured random variations did not support the commonly accepted hypothesis of similarity between the responses to turbulent flow of sediment concentration and temperature. The normalized turbulent intensities for all the measured veloc¬ity components showed their highest values during the period of lowest sediment concentration; this result is consistent with the hypothesis of turbulent intensity damping by suspended sediment.
Ano: 1989
Autor(es): Costa, R.
Editor: ******
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Alimentação artificial de praias
A contribution to increased use and development of the method of artificial nourishment of beaches is the main objective of this thesis. It also aims at being a guide for the design of the reconsctrution or outright creation of beaches.In the first chapter, the subject is introduced and the objectives of the thesis are outlined. The second chapter cover´s some general considerations on littoral dynamics, beach equilibrium and sediment budget.Since the theoretical foundations of the artificial nourishment of beaches still leave much to be desired, a description of this method and its principles are presented in the third chapter. Important technical and economic aspects are included, such as: sampling, analysis and characterization of native and borrow material; selection Of nourishment sources; extraction and transport of borrow sand; and characteristics of the theoretical final beach profile. Such problems as the integration of ecological aspects, and cost-benefit analysis are also treated.in the fourth chapter, the Portuguese experience in this domain is described. The experience of such countries as France and the U.S., where this method has frequently been used is also mentioned. In this way a considerable amount of hitherto scattered information is presented in a unified way.The fifth chapter, treats briefly the problem of coastal model similitude, both as a support for the experimental work: which was carried out and to help engineers in the design of a coastal physical model or in merely assessing the possibilities of such a model.In the sixth chapter, an experimental study is described of the influence of both the grain size of borrow material and the nourishment method on the redistribution of sediments after the nourishment. The obtained results are compared with existing theoretical methods and some prototype results.Finally, in the last chapter the main conclusions and recomendations of the thesis are presented.
Ano: 1987
Autor(es): Clímaco, M.
Editor: ******
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Solution of Advection-Dominated Transport by Eulerian-Lagrangian Methods Using Backwards Method of Characteristics
We provide a systematic analysis of the consistency, stability, convergence and accuracy of the numerical solution of the transport equation by a general Eulerian-Lagrangian Method (ELM). The method involvesthree basic steps: the backwards tracking of characteristic lines following the flow, the interpolation of concentrations at the feet of these lines, and the solution of dispersion taking such concentrations as initial conditions. The first two steps constitute the Backwards Method of Characteristics (BMC); the third step involves a time-discretization along the characteristic lines, and a spatial discretization of the dispersion operator, both based on conventional techniques (e.g.. Euler or Crank¬Nicholson for time; finite-elements or finite-differences for space).The choice of the spatial interpolator is shown to impact the consistency, stability and convergence, as well as the accuracy of the BMC. Most interpolators ensure consistency, but only a few ensure stability, hence convergence; stability criteria are derived from a newly developed generalized Fourier analysis, which can account for non-linearities introduced by quadratic grids. The comparison of formally derived propagation and truncation errors, complemented by numerical experimentation, provides a reference for the choice of the interpolator, given a specific transport problem characterized by prevailing concentration gradients.The BMC potentiates the use of large time-steps, well above Courant number of order one. In the limiting case of pure advection, optimal accuracy would be obtained for a At close to the total time of interest; the presence of dispersion constrains, however, the size of At, especially in the case of non-uniform flows. The comparison of the truncation errors for the three basic steps of ELM provides a reference to select At. as a function of Ax, of the spatial interpolators and time-discretization schemes, and of the gradients of flow and concentrations.
Ano: 1987
Autor(es): Melo Baptista, A.
Editor: ******
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Accurate Numerical Modeling of Advection-Dominated Transport of Passive Scalars. A Contribution
Apresenta-se um estudo sistemático, baseado simultaneamente em análises formais e em experimentação numérica, da precisão e estabilidade da solução da equação de transporte por um método Euleriana-Lagrangeana (MEL). 0 método decompõe a equação de transporte em equações separadas de advecção e de difusão, resolvendo a primeira pelo método das características regressivas no tempo (MCR), e a segundo por um método de elementos finitos, do tipo Galerkin.Mostra-se que as interpolações no espaço requeridas pelo MCR são um factor limitativo da precisão global do MEL, e comparam-se diversas técnicas alternativas de interpolação, algumas das quais originais. A combinação de esquemas compactos e não-compactos de interpolação, baseados em polinómios de Lagrange, é apontada como uma potencial solução óptima.Demonstra-se que, para uma adequada escolha do esquema de interpolação, o MCR é consistente, estável e convergente e tem boas características de precisão. Escolhas inadequadas do esquema de interpolação podem, no entanto, causar instabilidade e inconsistência.Estabelece-se a dependência da precisão do MCR no passo de cálculo, mostrando-se que essa precisão aumenta, em geral (para um tempo total fixo), quando se reduz o número de passos de cálculo, isto é, quando se aumenta o passo de cálculo (uma propriedade simultaneamente pouco habitual e muito conveniente). No entanto, na gama de valores muito pequenos do Número de Courant, a precisão é praticamente independente do passo de cálculo, o que evita que o método se torne divergente.Analisa-se brevemente o efeito de malhas irregulares e pluridimensionais sobre a aplicabilidade e precisão do MCR. Apesar de sensível à irregularidade da malha, o método mantém boas características de precisão desde que as distorções geométricas não sejam excessivas. Malhas pluri-dimensionais, quando simultaneamente irregulares, levantam problemas específicos de aplicabilidade de esquemas não-compactos de interpolação; esses problemas poderão se resolvidos através da utilização conjugada de esquemas compactos e não-compactos, para um mesmo problema. Investigação adicional a ainda requerida nestas áreas.Mostra-se ainda que a presença de mecanismos físicos de difusão beneficia tanta a precisão da solução da equação de advecção como a precisão global do MEL.Finalmente, demonstra-se a eficácia da aplicação do MEL (numa forma particular, restricta a esquemas de interpolação compactos) à simulação do transporte de poluentes em águas costeiras. 0 método permite, em particular, realizar simulações longas (várias marés) a custos moderados, mesma para malhas irregulares com elevado número de nós, e, também, evitar a necessidade do uso de difusividades artificiais como garante de estabilidade; em geral, e nestes dois aspectos em particular, o método revela-se superior a métodos Eulerianos, mais convencionais (por exemplo, métodos de elementos finitos, do tipo Galrkin ou Petrov-Galerkin, aplicados à equação de transporte indivisa).
Ano: 1986
Autor(es): Melo Baptista, A.
Editor: ******
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Sobre a Avaliação de Parâmetros de Qualidade de Água por Detecção Remota: Suspensões
No âmbito de um projecto de investigação intitulado caracterizarão de Formações Estuárias e do Meio Marítimo Litoral Por Técnicas de Detecção Remota , insere-se o estu¬do da avaliação de suspensões na água do mar com recurso à aplicação de técnicas de detecção remota como meio de caracterização de parâmetros de qualidade de água. 0 trabalho que se apresenta foi desenvolvido com os seguintes objectivos:1- Desenvolvimento de metodologias de análise e quantificação de suspensões na água do mar a partir de dados de satélite;2- Implementação sob forma de programas para computador de modelos de quantificação de suspensões orgânicas e inorgânicas na água do mar, a aplicar aos dados do radiómetro CZCS do satélite NIMBUS-7;3- Aplicação e verificação do modelo ao litoral português.Corn vista à consecussão destes objectivos, começa-se por apresentar uma extensa análise das formas de abordagem do problema, enumerando-se os diversos métodos actualmente seguidos, nomeadamente o Empírico, o Teórico e, neste, os métodos microscópico e macroscópico.Com base nesta análise, propõe-se um modelo numérico de quantificção das suspensões a partir dos dados do radiómetro CZCS do satélite NIMBUS-7, o qual, embora empírico na sua formulação como a maioria dos actualmente existentes, se apoia no comportamento radiomótrico da água do mar e dos seus constituintes típicos, cujas características se apresentam também.A implementação prática do modelo exige a filtragem da componente atmosférica presente nos dados rediométricos. Com este objectivo, apresenta-se um modelo baseado na metodo¬logia correntemente utilizada. Consiste na consideração da difusão simples, causada pelos constituintes básicos da atmosfera (moléculas gasosas, aerosóis e ozono) na gama de comprimentos de onda considerada (440, 520, 550 e 670nm). Esta metodologia conduz, porém, a um sistema de equações indeterminado e que é resolvido pela consideração de uma equação ´exterior´ ao processo de transferência radiativa que tem lugar na atmasfera. Para este efeito, utilizou-se a equação de Smith e Wilson por ser a mais divulgada, ressalvando-se, contudo, a necessidade de verificação da sua efectiva aplicação às águas do litoral português, o oqe não foi possível concretizar dada a inexistência de dados.
Ano: 1986
Autor(es): Oliveira, E. M.
Editor: ******
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Eulerian-Lagrangian Analysis of Pollutant Transport in Shallow Water
A numerical method for the solution of the two-dimensional, unsteady, transport equation is formulated, and its accuracy is tested.The method uses a Eulerian-Lagrangian approach, in which the transport equation is divided into a diffusion equation (solved by a finite element method) and a convection equation (solved by the method of characteristics). This approach leads to results that are free of spurious oscillations and excessive numerical damping, even in the case where advection strongly dominates diffusion. For pure diffusion problems, optimal accuracy is approached as the time-step, At, goes to zero; conversely, for pure-convection problems, accuracy improves with increasing At; for convection-diffusion problems the At leading to optimal accuracy depends on the characteristics of the spatial discretization and on the relative importance of convection and diffusion.The method is cost-effective in modeling pollutant transport in coastal waters, as demonstrated by an illustrative application to a case study (sludge dumping in Massachusetts Bay). Numerical diffusion is eliminated or greatly reduced, raising the need for realistic estimation of dispersion coefficients. Costs (based on CPU time) should not exceed those of conventional Eulerian methods and, in some cases (e.g., problems involving predictions over several tidal cycles), considerable savings may even be achieved.
Ano: 1984
Autor(es): Melo Baptista, A.
Editor: ******
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Sobre a Propagação de Ondas do Mar em Regiões Costeiras. Análise pelo Método dos Elementos Finitos
0 principal objectivo desta tese é mostrar a habilidade do métodos dos elementos finitos e do método dos elementos de fronteira na modelação das ondas gravíticas de superfície.Na análise linear, as equações reduzidas do movimento ondulatório são resolvidas pelo método dos elementos finitos, levando em linha de conta a reflexão parcial, a radiação e o atrito de fundo. A modelação da radiação é feita com elementos infinitos ou com elementos de radiação, sendo estes encarados como um caso particular dos elementos de reflexão. 0 atrito de fundo é introduzido após a discretização e é levado a efeito através de um coeficiente empírico que se pode relacionar com o coeficiente de Chezy.Quer o modelo determinístico quer o modelo estocástico, obtido do primeiro com base na noção do estimador natural, permitem a realização de ensaios de ressonância ou de agitação. Nos ensaios de ressonância de uma bacia portuária tem particular interesse o conhecimento do espectro de resposta ao ruído bran¬co de banda limitada.A título de exemplo de aplicação mostram-se alguns aspectos do estudo das condições de ressonância do porto de Leixões.Logo que não sejam válidas as hipóteses simplificativas que permitem uma abordagem linear das ondas gravíticas de superfície, são resolvidas as equações não lineares do movimento ondulatório com superfície livre, pelo método dos elementos de fronteira. As suas peculiaridades permitem, sem qualquer dúvida, considerar o método dos elementos de fronteira como o mais vocacionado para este tipo de análise.Os programas de cálculo automático para o estudo da análise não linear estão ainda em fase de teste, pelo que não se apresentam exemplos de aplicação.
Ano: 1982
Autor(es): Portela, A.
Editor: ******
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Numerical simulation of the tidal flow in homogeneous estuaries
Este trabalho é dirigido principalmente para o uso da simulação numérica dos escoamentos em estuários como uma ferramenta pa¬ra estudos de engenharia. Fazem-se algumas considerações gerais sobre a definição e classificação de estuários seguidas por uma descrição sumária da hidrodinâmica dos estuários. Descrevem-se e comparam-se as várias técnicas utilizadas na solução de problemas de hidradinâmica de stuários.Faz-se a dedução formal de um modelo matemático do escoamento em estuários homogéneos e integram-se verticalmente as suas e¬quações, obtendo-se as conhecidas equações do escoamento em águas pouco profundas ("shallow water equations"). Estas equações são discretizadas utilizando os métodos dos elementos finitos e das diferenças finitas, respectivamente no espaço e no tempo.Faz-se a descrição de um sistema de cálculo para determinar a solução do modelo matemático discretizado e tecem-se várias considerações acerca do seu desenvolvimento e uso.Finalmente apresentam-se os resultados de alguns testes utilizados para verificar o funcionamento do sistema de cálculo.
Ano: 1981
Autor(es): Figueira, P.
Editor: ******
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Estuarine and coastal morphodynamics
N/A
Ano: 2015
Autor(es): Fortunato, A. B.; Bertin, X.; Coco , G.; Concejo, A.; Dias, J. M.; Fernandes, E.; Larson, M.; Matias, A.; Oliveira, A.; Silva, P. A.; Dias, J. A.; Azeiteiro, U.; Costa , M.; Boski, T.
Keywords: coastal; Estuarine
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