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- Erosion of rocky shores- protection promoted by sandy beaches and shore platformsPublication . Moura, Delminda; Gabriel, Selma; Jacob, J.; Fortes, Conceição; Silva, Paulo A.; Horta, João; Abreu, TiagoO sector costeiro do Algarve central entre as praias da Galé e Olhos de Água deve a sua fisiografia crenulada a um sistema cársico bem desenvolvido em rochas carbonatadas. As arribas possuem no sopé uma plataforma litoral rochosa ou uma praia arenosa. Os principais objectivos do projecto de investigação EROS são: (i) a quantificação da dissipação da energia das ondas ao longo de plataformas litorais e de praias arenosas com diferentes declives e exposição às ondas; (ii) a caracterização da refracção e difracção das ondas e da modificação das correntes forçadas pelo controle morfológico. A metodologia base centra-se na aquisição de dados de ondas e correntes utilizando transdutores de pressão e correntómetros colocados em transeptos normais à linha de costa, de modo a obter o espectro completo de ondas e correntes, desde a água profunda até aproximadamente à base das arribas, quer nas plataformas quer nas praias.
- Integrated assessment of bioerosion, biocover and downwearing rates of carbonate rock shore platforms in southern PortugalPublication . Moura, Delminda; Gabriel, Selma; Gamito, Sofia; Santos, Rui; Zugasti, Estibaliz; Gomes, A.I.; Tavares, Ana Mafalda; Martins, Ana LuísaBioerosion on rocky shores has been frequently reported as an important mechanism in coastal evolution, with less attention focussed on determining the bioprotective role organisms may have in mediating coastal erosion. This work aims, for the first time, to provide an integrated assessment of both traversing microerosion meter (TMEM) downwearing rates and activity of intertidal organisms on two carbonate shore platforms in southern Portugal. Paired substations positioned on the same substrate but differing in biological cover (one with bare rock and the other with algal cover colonised between the first and final readings) were monitored for eighteen months using a TMEM. At each station, the volume of burrows produced by macro borers was measured. Downwearing rates were lower in the surfaces protected by algal turf except in the station that experienced the longest time of exposure to subaerial conditions. In contrast, TMEM downwearing rates were higher in the areas containing the higher volume of burrows. Both downwearing rates and burrow volumes were negatively correlated with the mechanical strength of the substrate as measured by Schmidt Hammer rebound.
- Downwearing rates on shore platforms of different calcareous lithotypesPublication . Moura, Delminda; Gabriel, Selma; Ramos-Pereira, Ana; Neves, Mário; Trindade, Jorge; Viegas, José; Veiga-Pires, C.; Ferreira, Óscar; Matias, Ana; Jacob, J.; Boski, T.; Santana, PauloVertical lowering (downwearing) of shore platform surfaces is a very important mechanism in their morphological evolution albeit much remains incompletely understood. The efficacy of mechanical and chemical weathering acting on a given substrate, together with erosional processes, influences downwearing rates. In order to determine the relationship between lithotypes and downwearing rates, data collected from a Transverse Micro-erosion Meter were obtained for shore platforms of three different calcareous lithotypes (biocalcarenite, calcarenite and carbonated siltstone) along the central Algarve coast (Southern Portugal). Downwearing rates ranged between 0.096 mm year−1 and 1.676 mm year−1 in biocalcarenite and weakly cemented calcarenite, respectively. In addition, physical properties of the rocks comprising the platforms were measured, including uniaxial compressive strength (as determined by the Point Load Test), porosity, and calcium carbonate content. The results show that downwearing depends primarily on the intrinsic properties of the substrate. Porosity, in particular, acts in two ways: (i) it tends to weaken the substrate; and, (ii) it controls the downward extent of the water percolation and therefore the depth of the weathering mantle subject to erosion by waves and currents.
- Morphological features and processes in the central Algarve rocky coast (South Portugal)Publication . Moura, Delminda; Albardeiro, L.; Veiga-Pires, C.; Boski, T.; Tigano, EsterMorphological features along the Algarve rocky coast, South Portugal, are identified and described, with an emphasis on shore platforms and notches. The contributions of processes, such as wave attack, chemical weathering and bioerosion, to sculpting the shore platforms are discussed. The preferential localization of shore platforms on sites exposed to waves, and the lack of significant chemical weathering, point to wave erosion as the first-order factor in platform formation, whilst bioerosion/bioprotection, lithology and geological structure determine platform morphological variations. In addition, platforms above the present intertidal zone appear to have a polygenetic evolution, being inherited from former sea-level highstands and currently undergoing chemical weathering. The occurrence of notch features is independent of the degree of exposure to waves, but they mostly occur where the substratum is sand. Hydrostatic pressure appears to be an important factor in the formation of marine caves in the more sheltered sites.
- Quaternary sea level highstands in the Algarve (South Portugal)Publication . Moura, Delminda; Albardeiro, L.; Veiga-Pires, C.; Boski, T.Algarve is the Portuguese southernmost region in which we can distinguish three main domains in the coastal zone. In the west coast, abrupt cliffs are cutting mainly Paleozoic schists and graywackes, prevailing small enclosed beaches with the largest sandy beaches being developed adjacently to the river mouths. In the windward side (west) of the south coast, cliffs were formed essentially into the Mesozoic and Miocene limestones.
- Wave transformation on shore platform and adjacent sandy beach - Southern PortugalPublication . Gabriel, Selma; Moura, Delminda; Horta, João; Oliveira, SóniaThe knowledge on coastal processes is not only of basic and practical importance (for instance in engineering applications) but also of socio-economic relevance. Crenulated coasts are complex geomorphic environments where both erosive (into headlands) and depositional processes (in embayed beaches) occur simultaneously. Waves represent an important morphogenic factor and the most important source of energy to coastal zones. However, field data reporting the interaction between waves and rocky coastal features is still scarce, leading to a poor understanding on rates and drivers of surf attenuation at rocky shores. Waves abrasion and erosion on shore platforms depend on the platform properties, morphology of the adjacent continental shelf, and water depth upon the platform surface, which is controlled by tides, available sediment and wave climate (e.g.,Stephenson and Kirk, 2000; Marshall and Stephenson, 2011). Shore platforms extending in the intertidal zone at the rocky cliffs’ toe are natural morphological barriers to wave propagation and energy attenuation (Ogawa et al., 2011). Over short time scales the beaches in a crenulated coast are modified mainly by waves causing setup and set down in the surf zone leading to a very complex pattern and circulation modified by the interaction between the currents induced by waves and the incident waves. The mechanisms involved in morphological modifications in those environments are still not well understood (Silva et al., 2010). This work aims to compare the waves behavior both on a shore platform and adjacent pocket beach in response to exactly the same offshore wave conditions.
- Coastal morphology along the Central Algarve rocky coast: driver mechanismsPublication . Moura, Delminda; Gabriel, Selma; Jacob, J.The boundary between the mainland and the sea – the littoral fringe - crosses several sub-environments, among them, the rocky coasts whose evolution depends on marine and sub-aerial processes as well as on the rocks’ mass properties. The study area - in central Algarve (South Portugal) - is framed in a rocky coast exposing carbonate rocks. This work identifies the main drivers to the coastal morphology in that region. Several morphological features such as beaches, cliffs, and shore platforms were surveyed, mapped, and correlated with the most common wave conditions in the area. Shore platforms show a strong correlation with the most vigorous wave climate conditions. In opposition, zeta bays occur in the more sheltered sector to the dominant waves and in a relatively straight coastline. Symmetrical small bays are mainly related with the sedimentary influx from rivers reaching the coast. The cliff heights and profiles are lithologically and structurally controlled.