Browsing by Author "Taborda, Rui"
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- Morphodynamics of fetch-limited beaches in contrasting environmentsPublication . Freire, Paula; Ferreira, Óscar; Taborda, Rui; Oliveira, Filipa; Carrasco, Ana Rita; Silva, Ana; Vargas, Catarina; Capitão, Rui; Fortes, Conceição Juana; Braga Coli, Alexandre; Santos, JoãoSandy beaches can be found in fetch-limited environments that are protected from ocean generated waves, as estuaries, lagoons, and backbarriers, and where fetch characteristics allow local wind-generated waves to develop and maintain a beach. The morphodynamics of these low-energy beaches present a peculiar behaviour and general open-ocean models are inappropriate for their study.
- Performance of intertidal topography video monitoring of a meso-tidal reflective beach in South PortugalPublication . Vousdoukas, Michalis; Ferreira, P. M.; Almeida, Luis Pedro; Dodet, Guillaume; Psaros, Fotis; Andriolo, Umberto; Taborda, Rui; Silva, Ana Nobre; Ruano, Antonio; Ferreira, ÓscarThis study discusses site-specific system optimization efforts related to the capability of a coastal video station to monitor intertidal topography. The system consists of two video cameras connected to a PC, and is operating at the meso-tidal, reflective Faro Beach (Algarve coast, S. Portugal). Measurements from the period February 4, 2009 to May 30, 2010 are discussed in this study. Shoreline detection was based on the processing of variance images, considering pixel intensity thresholds for feature extraction, provided by a specially trained artificial neural network (ANN). The obtained shoreline data return rate was 83%, with an average horizontal cross-shore root mean square error (RMSE) of 1.06 m. Several empirical parameterizations and ANN models were tested to estimate the elevations of shoreline contours, using wave and tidal data. Using a manually validated shoreline set, the lowest RMSE (0.18 m) for the vertical elevation was obtained using an ANN while empirical parameterizations based on the tidal elevation and wave run-up height resulted in an RMSE of 0.26 m. These errors were reduced to 0.22 m after applying 3-D data filtering and interpolation of the topographic information generated for each tidal cycle. Average beach-face slope tan(β) RMSE were around 0.02. Tests for a 5-month period of fully automated operation applying the ANN model resulted in an optimal, average, vertical elevation RMSE of 0.22 m, obtained using a one tidal cycle time window and a time-varying beach-face slope. The findings indicate that the use of an ANN in such systems has considerable potential, especially for sites where long-term field data allow efficient training.
- Relationship between wave energy and coastal morphology in the central Algarve rocky coast (Galé to Olhos de Água)Publication . Bezerra, Maria Margarida Tarrio Agreiro; Moura, Delminda; Ferreira, Óscar; Taborda, RuiThe coastal zones’ geomorphological evolution is the result of subaereal weathering and marine abrasion. To quantify the role of the waves’ action as a geomorphic process particularly on shore platforms sculpture is the main goal of the current work. For that purpose, a numerical modeling for wave propagation (STWAVE) was used to determine differences on breaking wave characteristics along the study area. This program was used inside an operational toolbox (SMS 9.2) that allows data pre-processing from a GIS software (ArcGIS 9.2). The MATLAB R2007a software was used to obtain significant wave heights and wave energy at the breaking position along the study area, for each tested condition. The different coastal morphologies and mass movements were identified on the field and compared with the described evolution in literature (Marques, 1997). Since the study area presents strong longshore variation in exposition to the waves and different wave energies, several sections were defined. It was then possible to analyze the frequency of occurrence of a given coastal morphology and the frequency of mass movements for each section and compare with longshore variations on wave energy for both average and storm conditions.
- The influence of wave action and lithology on sea cliff mass movements in central Algarve coast, PortugalPublication . Bezerra, Maria Margarida Tarrio Agreiro; Moura, Delminda; Ferreira, Óscar; Taborda, RuiThe 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.