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- Comparação morfológica e sedimentar de duas praias com diferente exposição às ondas (Praia da Galé e Praia de Olhos de Água)Publication . Oliveira, Sónia; Gabriel, Selma; Horta, João; Moura, DelmindaAs praias encastradas são sistemas semifechados, sendo por essa razão áreas de estudo interessantes. Neste trabalho estudou‐se duas praias com diferentes exposições face à ondulação dominante, Praia da Galé e Praia dos Olhos de Água. Como objetivo principal, pretendeu-se compreender as condicionantes morfológicas da área de estudo, através da análise granulométrica, topográfica e a sua relação com a agitação marítima. As associações granulométricas características de cada praia, estão relacionadas com fatores locais como o pendor, exposição face à onda incidente.
- 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.
- Retrieval of nearshore bathymetry from Landsat 8 images: a tool for coastal monitoring in shallow watersPublication . Pacheco, André; Horta, João; Loureiro, Carlos; Ferreira, OscarNearshore bathymetry is likely to be the coastal variable that most limits the investigation of coastal processes and the accuracy of numerical models in coastal areas, as acquiring medium spatial resolution data in the nearshore is highly demanding and costly. As such, the ability to derive bathymetry using remote sensing techniques is a topic of increasing interest in coastalmonitoring and research. This contribution focuses on the application of the linear transform algorithm to obtain satellite-derived bathymetry (SDB) maps of the nearshore, at medium resolution (30 m), from freely available and easily accessible Landsat 8 imagery. The algorithm was tuned with available bathymetric Light Detection and Ranging (LiDAR) data for a 60-km-long nearshore stretch of a highly complex coastal system that includes barrier islands, exposed sandy beaches, and tidal inlets (Ria Formosa, Portugal). A comparison of the retrieved depths is presented, enabling the configuration of nearshore profiles and extracted isobaths to be explored and compared with traditional topographic/bathymetric techniques (e.g., high- and medium-resolution LiDAR data and survey-grade echo-sounding combined with high-precision positioning systems). The results demonstrate that the linear algorithm is efficient for retrieving bathymetry frommulti-spectral satellite data for shallowwater depths (0 to 12 m), showing amean bias of−0.2m, a median difference of −0.1 m, and a root mean square error of 0.89 m. Accuracy is shown to be depth dependent, an inherent limitation of passive optical detection systems. Accuracy further decreases in areas where turbidity is likely to be higher, such as locations adjacent to tidal inlets. The SDB maps provide reliable estimations of the shoreline position and of nearshore isobaths for different cases along the complex coastline analysed. The use of freely available satellite imagery proved to be a quick and reliable method for acquiring updated mediumresolution, high-frequency (days and weeks), low-cost bathymetric information for large areas and depths of up to 12 m in clear waters without wave breaking, allowing almost constant monitoring of the submerged beach and the shoreface.
- The morphosedimentary behaviour of a headland–beach system: Quantifying sediment transport using fluorescent tracersPublication . Oliveira, Sónia; Moura, Delminda; Horta, João; Nascimento, Ana; Gomes, A.I.; Veiga-Pires, C.Embayed beaches occurring along rocky coasts with headlands controlling hydrosedimentary processes are considered to be constrained sedimentary systems with little longshore sediment transfer between them. Such beaches are likely to narrow under rising sea level and a deficit of fluvial sediment, and because beaches act to dissipate wave energy, cliff erosion is expected to increase. Knowledge of hydrosedimentary processes in fetch-limited environments such as embayed beaches is therefore a fundamental management tool in erosionprone coastal areas such as the Algarve region (southern Portugal). Themain objective of this work is to quantify longshore sediment transport (LST) using a sedimentary tracer and compare the resultswith the ones derived via empirical formulae from several authors. To achieve this, we establish the spatial and temporal patterns of stained sediment, and relate these to marine climate data over six tidal cycles for three adjacent embayed beaches. The values of displaced sand estimated using tracer and scaled to mixed layer depth were compared with the results of five well-known LST formulae to assess the applicability of eachmodel to mesotidal environments. Of the LST formulae used, the CERC (2013) shows to be the most accurate in our study area. This study demonstrates the efficacy of using tracers for tracking and quantifying the sediment transport and as a basis for assessing the viability of different LST formulae for representing transport in these types of environments. Thework also shows the importance of themorphological control of hydrosedimentary processes, including the disruption of longshore drift and the sediment transfer promoted by shore platforms.
- Moving sands along a headland-embayed beach system (Algarve, Southern Portugal)Publication . Oliveira, Sónia; Horta, João; Nascimento, Ana; Gomes, A.I.; Veiga-Pires, C.; Moura, DelmindaResilience of embayed and pocket beaches located at the southernmost coast of Portugal is currently a major question to coastal management of this region. In fact, several among those beaches have been artificially fed aiming to increase the width of the beach allowing people to maintain a safe distance to the unstable rocky cliffs.
- Mean sea level and coastline: Late QuaternaryPublication . Moura, Delminda; Gomes, A.I.; Gabriel, Selma; Horta, JoãoCoastal zones modified along the geological time forced by tectonic activity, climatic and mean sea level changes and thereby can preserve relevant information concerning past climatic and oceanographic conditions. During lowstands derived by glacial conditions, the coastline migrated seaward and, wide portions of the continental shelves where exposed to sub aerial evolution, the drainage net extended far away in the shelf and dune fields overspread favoured by dry cold conditions and vegetation scarcity. In contrast, during deglatiations, the mean sea level rose forcing the landward migration of the coastline leading to the landscapes submersion. The preservation of morphological features such as beaches, dunes and spit bars depended on several environmental variables and processes, such as, erosion, remobilization by currents, waves and mass movements and sedimentary burial. The relationship between the coastline and the mean sea level evolution along the Quaternary, as well as the environmental variables on the landscape preservation and remobilization are under discussion in this work.
- 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.
- Modelling the hydrodynamic and morphosedimentary response of an beach-headland system (Algarve, Southern Portugal)Publication . Horta, João; Oliveira, Sónia; Moura, DelmindaFuture behaviour of beaches within a headland-beach system is of fundamental interest on coastal evolution since they act as a buffer between the waves’ attack and the cliffs backing them. The beaches at the cliffs’ foot anchored between headlands are space-limited environments to morphosedimentary processes.
- Coastal paleokarst landforms: a morphometric approach via UAV for coastal management (Algarve, Portugal case study)Publication . Oliveira, Sónia; Moura, Delminda; Boski, T.; Horta, JoãoKarst landscapes display remarkable morphological diversity and raise challenging management questions. Understanding karst processes is particularly relevant to the management of densely populated rocky coastlines, since sea-level rise influences the erosion rate of potentially hazardous landforms (e.g. sinkholes). Appropriate management strategies are needed to mitigate against property loss and economic impacts on actively eroding karst. Coastal management in these areas should be based on accurate and reproducible measurements of karst features to better understand and predict their behaviour. Due to their inherent instability and frequent inaccessibility, detailed morphometric studies of exposed coastal sinkholes are limited. We demonstrate the utility of using an unmanned aerial vehicle (UAV) to provide rapid and accurate analysis of spatial data on a large density of sinkholes that would otherwise be inaccessible. UAV data were post-processed and analysed using geographical information (GIS) tools to characterize both individual sinkholes and their spatial distribution patterns. Our study was carried out on the rocky coast of the central Algarve (southern Portugal). As stated in many other previous works, sinkholes spatial distribution is mainly controlled by the network of fractures in the host rock that was also observed in our study area. In addition, the geometric properties and their differences between the studied sites are controlled by weathering processes and synoptic conditions. This research emphasises the geomorphic hazard associated with karst landscapes and reinforces the need to include knowledge about these landforms and their vulnerability to sea-level rise in integrated coastal management plans.
- The morphosedimentary behaviour of a headland–beach system: quantifying sediment transport using fluorescent tracersPublication . Oliveira, Sónia; Moura, Delminda; Horta, João; Nascimento, Ana; Gomes, A.I.; Veiga-Pires, C.Embayed beaches occurring along rocky coasts with headlands controlling hydrosedimentary processes are considered to be constrained sedimentary systems with little longshore sediment transfer between them. Such beaches are likely to narrow under rising sea level and a deficit of fluvial sediment, and because beaches act to dissipate wave energy, cliff erosion is expected to increase. Knowledge of hydrosedimentary processes in fetch-limited environments such as embayed beaches is therefore a fundamental management tool in erosionprone coastal areas such as the Algarve region (southern Portugal). The main objective of this work is to quantify longshore sediment transport (LST) using a sedimentary tracer and compare the results with the ones derived via empirical formulae from several authors. To achieve this, we establish the spatial and temporal patterns of stained sediment, and relate these to marine climate data over six tidal cycles for three adjacent embayed beaches. The values of displaced sand estimated using tracer and scaled to mixed layer depth were compared with the results of five well-known LST formulae to assess the applicability of each model to mesotidal environments. Of the LST formulae used, the CERC (2013) shows to be the most accurate in our study area. This study demonstrates the efficacy of using tracers for tracking and quantifying the sediment transport and as a basis for assessing the viability of different LST formulae for representing transport in these types of environments. The work also shows the importance of the morphological control of hydrosedimentary processes, including the disruption of longshore drift and the sediment transfer promoted by shore platforms.