Rui Taborda

Confidence limits of species proportions in microfossil assemblages

Abstract We analyzed the confidence limits of benthic foraminiferal counts obtained from fossil deep-sea assemblages to figure out the optimum number of specimens needed for a reliable interpretation of species proportions. Precision and reliability are analyzed by calculating the binomial confidence limits. We demonstrate that in studies based on the interpretation of the proportional distribution of only the dominant taxa, counts of as low as 100 specimens are sufficient. Studies, however, that aim to investigate species diversity patterns usually require higher counts. Generally, we suggest that percent abundance given in micropaleontological studies should include the binomial error estimate.

Field observations of sand-mixing depths on steep beaches

Abstract A series of field studies were carried out on three Portuguese beaches (Garra˜o, Faro and Culatra) to assess sand-mixing depths under a range of wave heights (0.34–0.80 m), wave periods (5.1–7.0 s) and mean grain sizes (0.26 and 0.38 mm). All the studied beaches had a reflective profile with a steep upper foreshore (tanβ of 0.10–0.14) and a more gentle low-tide terrace. In all experiments, plunging waves were breaking on the beach face. The study has identified a linear correlation between significant wave height at breaking ( H b ), and average sand-mixing depth ( Z m ), whereby Z m = 0.27H b . The empirical relationship is ten times larger than a previous one proposed by other authors working on gentle-slope dissipative beaches, and confirms previous findings on similar reflective beaches carried out in the USA. It was also confirmed that Z m is related to wave period, but does not seem to be a function of mean sand size.

Implications of Sea-Level Rise for Continental Portugal

Abstract The Portuguese coastline has a high diversity of coastal types, which will react differently to an accelerated sea-level rise. Estuaries and coastal lagoons will be most affected by a rising sea level. Amongst these, the Sado and Tagus estuaries and the Ria de Aveiro and the Ria Formosa coastal lagoons are probably the ones where socioeconomic impacts resulting from accelerated sea-level rise would be greatest. Sandy shores will face increased erosion. However, it is likely that at this type of coast other factors, such as sand deficiency caused by damming river basins, will continue to play a larger role in erosion than accelerated sea-level rise. Hard rocky coasts will be the least affected by accelerated sea-level rise. Specific adaptation policies for accelerated sea-level rise impacts do not presently exist in Portugal. However, existing laws can be used to prevent and/or reduce socioeconomic impacts if they are strictly applied. A strong commitment to coastal management by Portuguese authorities is therefore necessary in order to prevent and minimise future implications of accelerated sea-level rise.

Title: MICORE: DUNE EROSION AND OVERWASH MODEL VALIDATION WITH DATA FROM NINE EUROPEAN FIELD SITES

In this paper we present the first results of beach profile hindcasting with XBeach using recently measured coastal data acquired under storm conditions at eight European sites, including a comparison to model results obtained with off-the- shelf models. The results show consistently that the XBeach has skill in predicting the coastal profile, albeit that in most cases the erosion around the mean water line is overpredicted and the depositions at the lower beach face are overpredicted. The causes for this model effect are under active investigation but not resolved yet. Likely candidates are the modeling of onshore (asymmetry) transports which reduces the offshore transports due to undertow (currents) or the modeling of sediment motion in the swash zone.

Clam dredging effects and subsequent recovery of benthic communities at different depth ranges.

This study aimed to assess the potential effects of clam dredging and the subsequent recovery of the benthic environment. Two experimental areas located at 6 and 18m depth were established in order to analyse whether impacts and recovery of benthic environment are depth-related. Study areas were located within an area closed to dredging and two different plots were established at both depths. One of the plots was subjected to intense clam dredge-fishing, while the other was undisturbed and therefore used as control. Sampling followed a BACI design, with samples for macrobenthic, meiobenthic and sediment particle size analysis being taken by SCUBA divers from both areas before and after fishing stress. For both depths, impacts on the benthic environment were very low resulting in high recovery rates. Nevertheless, at shallower depths communities demonstrated a faster recovery. It was shown that depending on the faunal component used as a bioindicator, different results can be observed. Generally deposit-feeding organisms with scales or chitinous plates and vermiform shape (mainly crustaceans, polychaetes and ophiuroids), without external protection, were the most affected by dredging, while some polychaetes without external protection and with a carnivorous feeding mode seemed to be enhanced by fishing. The low level of perturbations induced by the dredging activities was comparable to the impact of surface waves on the bottom, as experiments were undertaken in wave-dominated environments. The coexistence of storm events during the study period proved to have similar or even more deleterious effects on the benthic environment. It appears that communities from hydrodynamic fishing grounds that are well adapted to natural physical stress are not highly affected by dredging.

Influence of Wave Action and Lithology on Sea Cliff Mass Movements in Central Algarve Coast, Portugal

Abstract The vulnerability of a rocky cliff to direct wave attack is a function of its lithological, structural, and morphological characteristics. The intensity of wave attack at the cliff foot depends on incident wave characteristics, nearshore bathymetry, beach and shore platform topography, coastline orientation, storm surges, and tidal range. The main goal of this paper is to relate the role of wave action as a geomorphic process influencing coastal cliff erosion with the control imposed by lithological and structural characteristics. For that purpose, a numerical wave propagation model (STWAVE) was used to evaluate differences in breaking wave height and energy along the study area (Galé–Olhos de Água, South Portugal) for a set of representative wave conditions and compared with existing mass movement data. As the study area presents wide longshore variation in wave exposition and breaking wave energies, five sectors were defined with contrasting wave action. When the distribution of mass movements along the coast is analyzed without considering the lithological variation, there is no relationship between the number and displaced volumes of mass movements and wave energy for each sector, with the majority of the movements and the greater volumes occurring in the least energetic sector. Therefore, lithology represents the dominant control on mass movement occurrence. However, if lithological variation is controlled by analyzing only the most common lithology in the study area (Miocene carbonate rocks), spatial variations in nearshore wave energy driven by the interaction of wave conditions with coastline orientation are found to influence mass movement occurrence. Resumo Os factores que condicionam a evolução de arribas rochosas são variados, incluindo processos continentais, marinhos e factores intrínsecos ao próprio substrato rochoso. Por exemplo, a vulnerabilidade das rochas ao ataque directo das ondas é igualmente função das suas características litológicas e estruturais. Por sua vez, a intensidade do ataque às arribas rochosas pelas ondas depende de características das ondas, da batimetria, da topografia das praias e plataformas de abrasão adjacentes, da orientação da linha de costa, da existência de sobreelevação do nível do mar e da amplitude das marés. O sector costeiro de arribas rochosas do Algarve central (Galé a Olhos de Água), proposto para estudo, expõe principalmente a Formação Carbonatada de Lagos-Portimão, do Miocénico. Constitui excepção o sector entre as praias de S. Rafael e da Baleeira, onde as arribas litorais expõem margas do Cretácico e calcários do Jurássico. O principal objectivo deste trabalho é definir o papel da acção das ondas, como um processo geomórfico, na erosão de arribas costeiras e comparar com o controlo imposto pelas características litológicas e estruturais das rochas. Para tal, foi utilizado um programa de modelação da agitação marítima (STWAVE) para determinar diferenças nas características das ondas na rebentação, ao longo do troço costeiro em estudo. A altura e energia das ondas na rebentação foram obtidas para cada condição testada e foram comparadas com os dados de movimentos de massa existentes. Uma vez que a linha de costa da área de estudo mostra uma forte variação longilitoral em relação à sua exposição às ondas, foram definidos cinco sectores com diferentes orientações. Dada a orientação diferenciada dos troços e a variabilidade longilitoral nas geoformas que os constituem, foi possível analisar a frequência de ocorrência de uma dada geoforma ao longo de troços com igual litologia mas com diferente orientação à ondulação dominante. Os resultados deste trabalho apontam para uma clara diferenciação energética entre troços costeiros, em função da sua orientação e do rumo de agitação (ex. SW versus SE). Quando se faz uma análise dos movimentos de massa sem considerar as variações litológicas, não se observa nenhuma relação entre o número e volume deslocado dos movimentos de massa e a energia das ondas para cada sector, com a maioria dos movimentos e os maiores volumes a ocorrerem no sector menos energético. Assim, a litologia representa o factor de controlo dominante na ocorrência de movimentos de massa. Contudo, ao analisar apenas o tipo litológico mais comum na área de estudo (rochas carbonatadas do Miocénico), verifica-se que as variações longilitorais de energia das ondas derivadas da interacção das condições de onda com a orientação da linha de costa são determinantes na ocorrência de movimentos de massa nesta litologia.

COSMOS: A lightweight coastal video monitoring system

The use of video systems for coastal monitoring purposes experienced a huge development over the last years. The main aim of this work is to present a new lightweight video monitoring system (COSMOS) that has been developed to target several key characteristics including portability, low-cost, robustness and easy installation. These characteristics were accomplished through the use of standard IP surveillance cameras and in-house developed software to correct the relative large distortion induced by the use of cameras with non-metric lens. This monitoring system has already been successfully tested in several coastal and estuarine sites with different objectives, illustrating its versatility and wide range of applicability. Research efforts are being made so that these systems can provide reliable real-time beach state indicators turning them into a key element in what concerns coastal hazard warning systems.

Sedimentary constraints on the development of a narrow deep strait (Sao Sebastiao Channel, SE Brazil)

The São Sebastião Channel (SSC), which separates São Sebastião Island from the continent, is a deep elongated strait on the inner shelf of the São Paulo Bight (SE Brazil). The aim of this study is to explain why it is presently sediment starved, instead of forming a tombolo. Wave data were obtained from both a WW3 model database and buoy records, and wave propagation patterns from the SWAN numerical model. Grain size trend analysis of 579 surficial sediment samples from the strait and the surrounding region served to estimate the residual transport directions. Bedload sediment transport was computed considering in situ currents and bottom sediment grain size. Moreover, six seismic profiles and one gravity core were obtained in the strait in order to evaluate the hickness of the sedimentary deposits. The geometry of the SSC (X/B=0.3, where B is the breakwater or island diameter and X is its cross-shore distance to the mainland) predicts that a tombolo should be formed, and wave patterns confirm that it is a zone sheltered from both S and NE waves. Previous studies have shown that the hydrodynamics of the SSC is controlled by wind-driven currents, which are more intense in the eastern and central sectors of the strait. The western sector is currently covered by sandy mud, whereas very coarse to fine sand prevails in the deeper eastern sector. Sediment patterns show a trend to deposition of fine sediment in the western sector of the SSC and two main depocentres located at the northern limit of the study area and at the southern mouth of the strait. Sandy mud in the western sector forms a 40-m-thick deposit close to the outer limit of Araçá Bay, whereas the remainder of the SSC is covered by a very thin layer of sandy sediments. Dominance of mud in the depositional western sector suggests low availability of sand in the area. Therefore, despite the geometry and wave patterns of the SSC favouring the formation of a tombolo, the dominance of wind-driven currents and the low availability of sand determine that such a sedimentary feature cannot be formed, resulting in a deep strait.

Estuarine margins vulnerability to floods for different sea level rise and human occupation scenarios

ABSTRACT Rilo, A., Freire, P., Guerreiro, M., Fortunato, A.B., Taborda, R. 2013. Estuarine margins vulnerability to floods for different sea level rise and human occupation scenarios. Sea level rise (SLR) is increasing the risk of flooding in marginal low-lying estuarine areas. High water levels in estuaries are associated with the simultaneous occurrence of various phenomena ranging from high tidal levels to large fresh-water discharges. The intense and diverse human occupation of some of these marginal areas increases the flood vulnerability, endangering human lives and causing heavy economic and environmental losses. This issue becomes even more relevant since the European Floods Directive establishes mandatory guidelines to all member states regarding flood risk assessment, integrating flood maps with territorial characteristics. The present study aims to assess the vulnerability to floods of a specific area in Tagus estuary, by integrating hydrodynamic modelling results with land use cartography. Results suggest that about 16.1% of the estuarine marginal fringe could be flooded for the 2050 scenario, rising up to 23.7% for the 2100 scenario. Moreover, industrial and urban areas will be the most affected sites. Considering future development scenarios planned for that site, the results point to an increasing vulnerability of urban areas and therefore to the relevance of this knowledge in future planning and management guidelines as well as measures to adapt to SLR. The uncertainties and implications of the study are also discussed, and future research topics are indicated.

Seasonal to Decadal Variability of Longshore Sand Transport at the Northwest Coast of Portugal

AbstractLongshore sediment transport (LST) is a major driver of coastal evolution. However, despite the recognition that it presents an unsteady behavior at the seasonal scale, the variability at longer term scales (interannual and decadal) is still far from being properly acknowledged. The present work contributes to the understanding of the seasonal to decadal variability of the LST, benefiting from recent developments in wave hindcast modeling. This work was developed for the northwest coast of Portugal, which is fully exposed to the highly energetic wave regime generated in the Northeast Atlantic Ocean that induces unusually large LST rates. Hindcast offshore waves, between 1953 and 2010, were used as offshore forcing to deduce LST estimates. The mean annual LST, between 1953 and 2010, shows an irregular and noncyclic pattern. Computed mean annual LST, for this coastal stretch, is around 1 million cubic meters directed to the south, with yearly averages ranging from 108,000 to 2.24 million m3 year−1 a...