Artigos de Revista

Digital preservation aims at maintaining digital objects and making data accessible over long periods of time. The emerging context of e-Science imposes new scenarios and new requirements for digital preservation. This paper presents the main issues, current solutions and prominent projects for digital preservation and e-Science data management. Finally, it presents the problem to be addressed, the solutions to explore, the proposed methodology and expected contributions of the associated PhD work.

As estruturas de retenção têm vindo a ser cada vez mais utilizadas para o controlode cheias em áreas urbanas. O pré-dimensionamento destas estruturas é frequentementeefectuado através do método simplificado, também conhecido por métodoholandês, embora o dimensionamento final deva resultar da aplicação de um métodonumérico que tenha em consideração hietogramas de projecto, as características dabacia de drenagem, a geometria da estrutura de retenção e a lei de vazão dos órgãosde descarga.Dado que o dimensionamento com modelos distribuídos e hidrodinâmicos obriga àrealização de um conjunto alargado de simulações, desenvolveu-se um modelo numéricoque efectua automaticamente o cálculo iterativo das necessidades de armazenamento eda chuvada crítica de projecto, para diferentes opções de dimensionamento da estruturade retenção e dos órgãos de descarga.Os resultados obtidos pelo método holandês e pelo modelo numérico desenvolvido sãocomparados com os obtidos com o SWMM, para cenários seleccionados de um casode estudo. As potencialidades e limitações de cada método são discutidas à luz dainfluência das suas hipóteses de base nos resultados obtidos.

In this work, a video-monitoring system applicable to the study of beach morphodynamics was developed and applied to the DTM extraction of the intertidal zone of a fetch limited beach (Alfeite, Portugal). This low-cost system, intended to complement standard survey tools, has the additional benefit of enabling the continuousmonitoring of beach meso-scale process (spatial/temporal scales in the order of kilometers and years, respectively). The development of this system, based on terrestrial photogrammetric techniques, involved three main steps: i) camera calibration, where the internal camera parameters were determined in the laboratory using open-source software; ii) the development of image correction subroutines, which aimed to correct the relativelylarge image distortions induced by camera optics; this procedure revealed to be essential as the system was builtupon standard non-metric surveillance cameras; iii) the development of image rectification subroutines totransform oblique images into vertically equivalent images; this transformation was based on external camera orientation parameters obtained in the field through the surveying of ground control points. Alfeite beach DTM extraction was performed through the shoreline digitalization, in geo-referenced rectified images acquired every 10 min, during the flood. The overlapped set of shoreline curves, properly referred to a vertical datum by meansof tide measurements, characterized the intertidal beach morphology. The obtained results were compared with the ones acquired with classic survey techniques revealing very encouraging results; the overall vertical rms was 0.08 m with a maximum value of 0.15 m at 390 m of the camera.

O número de casos de estruturas de betão afectadas por reacções expansivas internas tem aumentado muito nos últimos anos, tanto em Portugal como a nível internacional. A degradação do betão por reacções químicas de origem interna engloba dois tipos de reacções expansivas: a reacção álcalis-sílica (RAS) e a reacção sulfática de origem interna (RSI). Estas duas reacções, que têm manifestações macroscópicas semelhantes (Figura 1), quando detectadas são muito difíceis de combater, não existindo ainda um método totalmente eficaz de reparação para estruturas degradadas por RAS ou RSI. Este aspecto salienta assim a necessidade da tomada de medidas mitigadoras contra a sua ocorrência no futuro.

A madeira é um material de construção versátil e com grande potencial. Noentanto, a sua susceptibilidade face à acção de agentes biológicos eatmosféricos condiciona muitas vezes o desempenho e a durabilidade dasestruturas de madeira. É assim fundamental ter estes aspectos em contadurante o projecto, a construção e a exploração das estruturas.

This paper describes a site specific study of a low energy estuarine beach sheltered from oceanic waves which presents a medium term (decade) geomorphologic stability. However, extreme meteorological events, characterized by strong winds, generate episodes of retreat of the beach face, which, under restored wave conditions, recovers in the short term. Three process-based models (a wind wave generation propagation model, a 2D-V littoral drift model and a 2D-V cross-shore morphodynamics model), frequently applied in open coastal areas but never in such low energy environments, were applied. The longshore transport was difficult to measure in the field and thus the numerical estimate was not validated. However, its uncertainty (9.6-16.1 x103 m3.year-1) was tested based on a sensitivity analysis of three influential parameters. Field measurements of meteo-oceanographic data and profile changes during a storm episode allowed the simulation of the hydrodynamics and sediment transport, and finally the verification of the numerical profile. Despite the volume of sediment extracted from the beach face being in good agreement with the observations, about 10m3.m-1, the profile geometry was not: the numerical profile exhibits an erosion scarp located bellow the retreat observed and a bar, at the beach face base, which was not observed in the field (probably flattened by the uprush and downrush flows). The effect of the passage of a catamaran was also evaluated: it generates an erosion of sediment up to 0.04m3.m-1 (depending on the catamaran velocity). Due to the beach geomorphologic characteristics the sediment transport is higher at higher tidal levels.

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Os tsunamis são talvez a única catástrofe natural capaz de causar destruição em zonas costeiras afastadas milhares de quilómetros da zona fonte. Eles podem causar perturbações significativas nas actividades portuárias devido a movimentos excessivos dos navios amarrados no seu posto de acostagem excitados por movimentos da superfície livre que podem ser quase imperceptíveis. Neste caso, o que importa é a gama de frequências presente nas forças de excitação actuantes no navio conter, ou não, as frequências próprias dominantes do conjunto navio/sistema de amarração. Para a maioria dos navios de carga estas frequências são mais baixas do que as associadas às da agitação marítima gerada pelo vento. Nesta comunicação revêem-se os tsunamis registados ao longo da costa portuguesa no século XX e apresenta-se o Sistema Nacional de Alerta contra Tsunamis (SNAT). Descreve-se também o projecto de investigação em curso para desenvolvimento de uma ferramenta integrada capaz de avaliar os efeitos de tsunamis em navios amarrados no interior de portos e de um procedimento para incorporar esses efeitos no SNAT.

The Ria de Aveiro, a mesotidal lagoon located on the Northwestern Portuguese coast, is characterized by large areas of intertidal flats and a web of narrow channels. The lagoon has a large area of mostly abandoned salt pans, whose progressive degradation is caused by the lack of maintenance and by the strong currents which erode their protective walls. The shallow water model ELCIRC was implemented and calibrated for the Ria de Aveiro in order to study its hydrodynamics, with special emphasis on the effect of the destruction of the salt pans protective walls. The calibration was performed by adjusting the bottom friction coefficient, through the comparison between measured and computed time series of surface water elevations at several stations within thelagoon. Harmonic analyses of these data were performed in order to evaluate the models accuracy. An assessment of root mean square errors and skill showed that a good calibration was achieved.Once calibrated, ELCIRC was used to characterize the hydrodynamics of the entire lagoon and the channels around the salt pans under different scenarios (present athymetry and a projection of the bathymetry resultingfrom the walls destruction). An extreme destruction of the salt pan walls would result in a significant increase of the inundation area in Ria de Aveiro, as well as in changes of the global and local hydrodynamic regimes. In summary, this study reveals how the increase of the flooded area in estuarine lagoons can affect tidalpropagation, including the increase of tidal currents, tidal prism and tidal asymmetry. The long-term implications of the salt pans inundation are discussed based on the results.