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- Field measurements and hydrodynamic modelling to evaluate the importance of factors controlling overwashPublication . Matias, Ana; Carrasco, A.R.; Loureiro, Carlos; Masselink, Gerd; Andriolo, Umberto; McCall, Robert; Ferreira, Oscar; Plomaritis, Theocharis; Pacheco, André; Guerreiro, MarthaOverwash hydrodynamic datasets are mixed in quality and scope, being difficult to obtain due to fieldwork experimental limitations. Nevertheless, these measurements are crucial to develop reliable models to predict overwash. Aiming to overcome such limitations, this work presents accurate fieldwork data on overwash hydrodynamics, further exploring it to model overwash on a low-lying barrier island. Fieldwork was undertaken on Barreta Island (Portugal) in December 2013, during neap tides and under energetic conditions, with significant wave height reaching 2.6 m. During approximately 4 h, more than 120 shallow overwash events were measured with a video-camera, a pressure transducer and a current-meter. This high-frequency fieldwork dataset includes runup, overwash number, depth and velocity. Fieldwork data along with information from literature were used to implement XBeach model in non-hydrostatic mode (wave-resolving). The baseline model was tested for six verification cases; and the model was able to predict overwash in five. Based in performance metrics and the verification cases, it was considered that the Barreta baseline overwash model is a reliable tool for the prediction of overwash hydrodynamics. The baseline model was then forced to simulate overwash under different hydrodynamic conditions (waves and lagoon water level) and morpho-sedimentary settings (nearshore topography and beach grain-size), within the characteristic range of values for the study area. According to the results, the order of importance of factors controlling overwash predictability in the study area are: 1st) wave height (more than wave period) can promote overwash 3–4 times more intense than the one recorded during fieldwork; 2nd) nearshore bathymetry, particularly shallow submerged bars, can promote an average decrease of about 30% in overwash; 3rd) grain-size, finer sediment produced an 11% increase in overwash due to reduced infiltration; and 4th) lagoon water level, only negligible differences were evidenced by changes in the lagoon level. This implies that for model predictions to be reliable, accurate wave forecasts are necessary and topo-bathymetric configuration needs to be monitored frequently.
- Towards assessing the resilience of complex coastal systems: examples from Ria Formosa (South Portugal)Publication . Kombiadou, Katerina; Matias, Ana; Carrasco, Rita; Ferreira, Oscar; Costas, S.; Vieira, G.The present paper contributes to assessing the resilience of a complex barrier island environment, namely of the Ria Formosa multi-inlet system in southern Portugal. The long-term morphologic evolution of four study areas during the last 60 years (1947 to 2014) is analysed based on aerial photographs, including the environments of oceanic and backbarrier beaches, dunes and salt marshes. The results show that each study area responded to external drivers (inlet stabilisation works, storms, etc.) differently, evolving in distinct patterns during the study period. All four study areas appear resilient to external pressures and/or forcing conditions, since they are either transforming (Barreta and Culatra islands), or adapting (Cabanas island and Cacela peninsula) or remaining stable at a near-equilibrium state (Tavira island). Based on the analysis of the multi-decadal evolution of the sites, four resilient barrier states are identified, related to the maturity and growth of the barrier. In the next stages, the research will focus on the relation between medium to short-term changes, aiming at understanding the response and feedbacks of the environments to specific drivers of change and relating them to resilience indicators.
- Managing flood risk in fetch-limited environmentsPublication . Carrasco, Ana Rita; Ferreira, Óscar; Matias, AnaThere is little unanimity concerning the environmental modifications potentially forced by the acceleration of global climate change in the coming century, or the future actions required to work towards a sustainable development of natural habitats in the coastal zone. A simple framework to assess the potential implications of flooding in fetch-limited coastal environments (with no relevant wave setup), experiencing both coastal and river flooding, was recently developed. It identifies tide, storm surge, sea level rise and river discharge as the main sources of flooding hazards. Hazard maps differentiate distinctive zones of flooding: the constantly flooded zone, the frequently flooded zone, and the infrequently flooded zone. The framework prioritizes site-based local management, and identifies alternative tools for sustainable coastal resources, to face non-desired flood effects. It was applied to a morphologically complex (tidal channels network, salt marshes, dunes) occupied backbarrier coastal stretch located in Culatra Island, South Portugal (max. fetch ~ 4 km). The obtained inundation levels predicted for 1, 10 and 100 year-return periods were 2.02 m, 2.39 m, and 2.84 m above MSL, respectively. The high-, moderate-, and low-risk zones include about 34 m2 , 1,073 m2 and 31,821 m2 of occupied area, respectively. Besides houses, flood impacts also affect other infrastructures (e.g., walkways and recreational structures). Several best practices principles and guidelines were proposed for the three risk zones, namely the adaptation to uses with ‘added value’, which enhances the local ecological values and strengths economic activities. This study contributes to the method validation at a complex morphological area and enriches the understanding about the potential of flood in fetch-limited conditions, praising the perspective of ‘living with climate change’.
- Morphodynamic evolution of fetch-limited beachesPublication . Carrasco, Ana R.; Ferreira, Óscar; Freire, Paula Maria dos SantosThis thesis examines the morphodynamic evolution of a fetch-limited backbarrier beach located in the Ria Formosa barrier island system. Three different scales of analysis were ascribed: a short-term scale, a medium-term scale, and a long-term scale. Main issues addressed were: (a) the factors governing sediment transport under very limited-fetch conditions; (b) the morphological evolution at medium to long-term, and (c) the role of human interventions in beach morphology. At short-term (over the tidal cycle) sediment transport patterns were locally determined by employing fluorescent tracer techniques, and quantifying morphologic variations and transport rates. The medium- to long-term evolution (between months and from years to decades) was set based in topographic surveys and aerial photograph analysis. Finally, a general framework was developed for flood hazard assessment at fetch-limited coastal environments. This framework embraces the hazard zones identification, risk analysis and the associated most reasonable management options.
- Relatório setor segurança de pessoas e bens: vulnerabilidades atuais e futurasPublication . Ferreira, Andreia; Oliveira, André; Dias, Luís Filipe; Fernandes, Luís; Brito, David; Braunschweig, Frank; Sampath, Ruwan; Moura, Delminda; Mendes, Isabel; Carrasco, A. Rita; Costas, Susana; C. Veiga-Pires, C.As alterações no clima constituem um fator a ter em conta no setor da segurança de pessoas e bens. Muitos dos impactos associados às alterações climáticas exacerbam ou alteram ameaças já existentes, como aquelas associadas a eventos extremos, inundações e secas (Sperling e Szekely, 2005). Os cenários de alterações climáticas projetados para Portugal tornam necessário um esforço de adaptação do Sistema de Proteção Civil face à probabilidade do aumento da ocorrência de eventos meteorológicos extremos, na medida em que poderá ocorrer um aumento de fenómenos em que a segurança de pessoas e bens seja colocada em causa. A este nível, a Estratégia Nacional de Adaptação às Alterações Climáticas (ENAAC) indica que as medidas de adaptação face às alterações climáticas, no contexto da segurança de pessoas e bens, se devem desenrolar em duas principais linhas de atuação.
- Backbarrier evolution at a medium-term scalePublication . Carrasco, Ana Rita; Ferreira, Óscar; Matias, Ana; Freire, Paula; Dias, J. A.This study reports the medium-term evolution of a sandy backbarrier and its relation with prevailing wind conditions. Obtained results demonstrated that Ancão backbarrier does not behave as a scale-down version of higher energy fetch-limited or oceanic beaches, being considered as a low-energy beach with extremely low wind-induced wave conditions. Volumetric changes during the three years monitoring were small, and the analysis of low-scale changes was divided into four beach compartment: upper beach, beach face, tidal flat, sand bank. There was no significant correlation between prevailing wind conditions, volume and grain-size variation, neither a marked seasonal pattern. Some wind-induced beach changes were perceptive in the grain size variations, related mostly to aeolian offshore sediment transport. Morphological changes were similar in the upper part of the profile, including upper beach and beach face, with changes mostly related to wind and windwaves energy. The lower part of the profile, which includes the tidal flat and the sand bank, frequently react independently from the upper part of the profile, although, sediment exchange between them was noticed during extreme conditions. The lower part of the profile had larger volumetric variability, without any evident wind dominance. The studied beach revealed high morphologic resilience, yet the overall quantities of sediment transported between 2005 and 2008 has particular relevance in the local coastal management context. Further research is needed to develop a broad-scale model of fetch-limited beaches, including the less energetic settings of the spectra such as backbarrier environments.
- Historic monuments threatened by coastal hazards at Boca do Rio, Algarve, PortugalPublication . Carrasco, A. Rita; Ferreira, Óscar; Matias, Ana; Dias, J. A.The coastal stretch of Boca do Rio, western Algarve, Portugal, is experiencing shoreline retreat. Roman ruins are located along the beach section of the coast, and a 17th-century fort is positioned over the cliff section. Both historic monuments are being destroyed by erosion but need to be protected due to their heritage status. Aerial photograph analysis was used to define the evolution of the coast for the period 1945–2001. Shoreline retreat of 0.3 m/year was measured for the sandy coast and 14 mass movements in the cliff face were identified. Considering the rate and style of shoreline evolution, several types of management scenario were evaluated, with the favored measures being the removal of the Roman ruins to a museum and the relocation of the fort inland.
- A multi-sensor approach to monitor the ongoing restoration of edaphic conditions for salt marsh species facing sea level rise: An adaptive management case study in Camargue, FrancePublication . Davranche, Aurélie; Arzel, Céline; Pouzet, Pierre; Carrasco, Rita; Lefebvre, Gaëtan; Lague, Dimitri; Thibault, Marc; Newton, Alice; Fleurant, Cyril; Maanan, Mohamed; Poulin, BrigitteThe Camargue or Rhone delta is a coastal wetland in southern France of which parts formerly devoted to salt production are undergoing a renaturation process. This study assessed a multisensor approach to investigate the link between sediment size distribution, habitat development mapped with Worldview 2, flooding durations estimated with time series of SENTINEL 2 images and elevation modelled with a LIDAR point cloud in former saltworks. A Random Forest classification algorithm was used to map the vegetation distributions of Sarcocornia fruticosa and Arthrocnemum macrostachyum, main representatives of the NATURA 2000 "Mediterranean and thermo-Atlantic halophilous scrubs (Sarcocornetea fruticosi)" habitat on the site. The best habitat map was ob-tained when considering the species separately. The random forest Out-of-bag errors were 1.43 % for S. fruticosa and 2.18 % for A. macrostachyum. Both species were generally distributed on different elevation and flooding duration zones considering mean values. Flooding duration was estimated with the Water In Wetland index (WIW) based on 15 Sentinel-2 scenes. Two models related to sediment grain size distribution were developed: one predicting the flooding duration and one predicting the halophilous scrub distribution. Maps of flooding duration, sediment grain size distribution and elevation highlighted two main zones in the study area: a western section with coarser sediments, shorter flooding durations and higher elevations under sea influence; an eastern section with finer sediments, longer hydroperiods and lower elevations under a historic river influence. This multidisciplinary approach offers perspectives for using space-based data over large scales to monitor changes in edaphic conditions of coastal areas facing natural and anthropogenic forcings. The results call for further in-vestigations to predict the dynamic distribution of other coastal habitats following climate change impacts, such as sea level rise.
- Overtopping hazard on a rubble mound breakwaterPublication . Carrasco, A. Rita; Reis, Maria T.; Neves, Maria G.; Ferreira, Oscar; Matias, Ana; Almeida, SílviaA major concern of coastal engineering is not only to access the damage to coastal structures by severe wave overtopping, but also the hazard imposed to users. Local hazard is often associated to the volume of overtopping water per unit of time (called overtopping discharge). Despite two decades of intensive research, it is yet not fully clear to practitioners what is the best method to compute the discharge parameter and its application on the assessment of local hazard. This work provides insight into the overtopping characterization in rubble mound breakwaters, by distinguishing different methods to assess hazardous overtopping. Fieldwork was conducted over a tidal cycle in a breakwater located at Albufeira Harbour (South coast of Portugal) under storm conditions (Hso~ 3 m; Tp ~ 9 s). Mean overtopping discharges were calculated from field measurements of flow depths and velocities at the breakwater slope armour and at the impermeable crest. Two different velocities were calculated: overtopping leading-edge velocity and overtopping peak velocity. The two methods provided similar results, with higher velocities occurring during high-tide (between 2 and 10 m/s). Mean overtopping discharges at the beginning of the impermeable crest ranged between 0.2 and 0.8 l/s/m. Under the measured hydrodynamic conditions, the breakwater offers risk to all types of pedestrians. Additionally it is shown that field measurements compare relatively well with empirical prediction methods (for the overall analysed overtopping events), namely the corrected NN_OVERTOPPING2 neural network tool. Besides contributing to the overall database on wave overtopping in coastal structures, the presented results can also be used for calibration and validation of overtopping evaluation methods (empirical formulae, artificial neural networks and numerical and physical models).
- Barrier island resilience assessment: Applying the ecological principles to geomorphological dataPublication . Kombiadou, Katerina; Matias, Ana; Costas, Susana; Carrasco, A. Rita; Plomaritis, Theocharis A.; Ferreira, ÓscarApplying the ecological resilience principles to barrier island geomorphological evolution requires approaches that perceive and interpret resilience far from predefined barrier characteristics and static views. Accepting that barrier islands, like all natural systems, are dynamic and adaptively changing in response to external disturbances is fundamental to the formulated approach. To this aim, geomorphological units and dimensions were used to describe barrier island stability landscape as an actively shifting ‘topography’, reshaping in response to exogenous events and in relation to intrinsic properties. The structure of the subaerial barrier was characterised using the environmental units of Beach, Dune and Marsh (or BDM), where different combinations of BDM structure define distinct barrier stable states, under a simplified framework that is applicable over a wide range of barrier structures. The methodology is based on reconstructing resilience trajectories of barrier islands through identifying the distinct BDM states and related shifts (thresholds crossed) and assessing resilience dimensions (latitude, resistance and precariousness defined as barrier width and height and proximity to mainland, respectively) that, jointly, define the shape of the stability domain. The approach was applied to the Ria Formosa barrier island system (S. Portugal), using multi-decadal geomorphological data and gradually decreasing spatial discretisation, passing from individual barrier transects to sectors and to entire barriers. The joint evolution of two inland-migrating barriers (Cabanas Island and Cacela Peninsula) was used as an exemplar of adaptive capacity in barrier geomorphic change and, therefore, of resilient response to external pressures. Resilience pathways showed that the Ria Formosa barriers have been resilient over the studied timeframe, with a tendency for maintaining or increasing BDM structural complexity. In general, the stability domain tends to shift from low latitude and high resistance forms (narrow-deep basins of attraction) in the west part of the barrier chain, to higher latitudes and lower resistance ones (wide-shallow basins) towards the east. Precariousness peaks near the edges of the system (low lagoon width) and minimises towards the central part (most detached barriers). Scaling issues regarding smoothing of longshore variability and potential consequences on masking thresholds and critical dimensions are highlighted and discussed, along with the key role of the meaning of specified resilience (of what?) in the assessment. The methodology is a novel approach, easily transferable to different systems and spatiotemporal scales of analysis, representing a step forward in interpreting and assessing barrier island resilience.