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- CRAF Phase 1, a framework to identify coastal hotspots to storm impactsPublication . Ferreira, Óscar; Viavattene, Christophe; Jimenez, Jose; Bole, Annelies; Plomaritis, Theocharis; Costas, Susana; Smets, StevenLow-frequency high-impact storms can cause flood and erosion over large coastal areas, which in turn can lead to a significant risk to coastal occupation, producing devastation and immobilising cities and even countries. It is therefore paramount to evaluate risk along the coast at a regional scale through the identification of storm impact hotspots. The Coastal Risk Assessment Framework Phase 1 (CRAF1) is a screening process based on a coastal-index approach that assesses the potential exposure of every kilometre along the coast to previously identified hazards. CRAF1 integrates both hazard (e.g. overwash, erosion) and exposure indicators to create a final Coastal Index (CI). The application of CRAF1 at two contrasting case studies (Ria Formosa, Portugal and the Belgian coast), validated against existing information, demonstrates the utility and reliability of this framework on the identification of hotspots. CRAF1 represents a powerful and useful instrument for coastal managers and/or end-users to identify and rank potential hotspot areas in order to define priorities and support disaster reduction plans.
- 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.
- Regional assessment of storm related overwash and breaching hazards on coastal barriersPublication . Plomaritis, Theocharis A.; Ferreira, Óscar; Costas, SusanaCoastal communities are threatened by the impact of severe storms that may cause significant loss of life and damage to properties. Among the main processes behind such impacts on coastal barriers are the occurrence of overwash and breaching during storm events. In order to estimate potential losses associated with a particular event, the above processes must be properly parameterized. Here, we propose a novel methodology to estimate overwash and breaching hazards suitable for a regional scale analysis (Ø 100 km). For the overwash hazard assessment, the method is based on the application of the approach developed by Donnelly (2008) that allows the parametrisation of the overwash hazard considering both flow velocity and flow depth. Moreover, the inland extension of the associated hazard, which is critical to assess subsequent vulnerability, can also be estimated following this methodology. The proposed method requires the selection of a runup formula validated for the study area, a storm beach profile, a runup lens angle, and a percolation constant for infiltration. To assess the breaching, hazard, a new multivariable evaluation is proposed that allows ranking the potential of breaching. The multivariable evaluation combines overwash and erosion hazards as well as their extensions with the main morphological characteristics of the barrier, resulting in the breaching hazard index, that ranks from 0 to 5 (no breaching to inlet formation). Inland breaching extension is also relevant for the vulnerability assessment. The breaching extension can be estimated using historical or contemporary analogues of the nearest flood deltas. The developed approaches were applied to Ancão Peninsula (Algarve, Portugal) as a demonstration example. The advantages of the present approach are: adaptability to various environments where overwash and/or breaching processes are important, time efficiency on evaluating overwash and breaching hazards, and the assessment of hotspot areas at a regional scale.
- Estimating the optimum size of a tidal array at a multi-inlet system considering environmental and performance constraintsPublication . González-Gorbeña Eisenmann, Eduardo; Pacheco, André; Plomaritis, Theocharis; Ferreira, Oscar; Sequeira, ClaudiaThis paper investigates the optimum tidal energy converter array density at a tidal inlet by applying surrogate-based optimisation. The SBO procedure comprises problem formulation, design of experiments, numerical simulations, surrogate model construction and constrained optimisation. This study presents an example for the Faro-Olhão Inlet in the Ria Formosa (Portugal), a potential site for tidal in-stream energy extraction. A 35 kW Evopod™ floating tidal energy converter from Oceanflow Energy Ltd. has been used for array size calculations considering two design variables: (1) number of array rows, and (2) number of tidal energy converter per row. Arrays up to 13 rows with 6–11 tidal energy converters each are studied to assess their impacts on array performance, inlets discharges and bathymetry changes. The analysis identified the positive/negative feedbacks between the two design variables in real case complex flow fields under variable bathymetry and channel morphology. The non-uniformity of tidal currents along the array region causes the variability of the resource in each row, as well as makes it difficult to predict the resultant array configuration interactions. Four different multi-objective optimisation models are formulated subject to a set of performance and environmental constraints. Results from the optimisation models imply that the largest array size that meets the environmental constraints is made of 5 rows with 6 tidal energy converter each and an overall capacity factor of 11.6% resulting in an energy production of 1.01 GWh year−1. On the other hand, a higher energy production (1.20 GWh year−1) is achieved by an optimum array configuration, made of 3 rows with 10 tidal energy converters per row, which maximises power output satisfying environmental and performance restrictions. This optimal configuration permits a good level of energy extraction while having a reduced effect on the hydrodynamic functioning of the multi-inlet system. These results prove the suitability and the potential wide use of the surrogate-based optimisation method to define array characteristics that enhance power production and at the same time respect the environmental surrounding conditions.
- Reply to: Sandy beaches can survive sea-level risePublication . Vousdoukas, Michalis I.; Ranasinghe, Roshanka; Mentaschi, Lorenzo; Plomaritis, Theocharis A.; Athanasiou, Panagiotis; Luijendijk, Arjen; Feyen, Luc
- 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.
- Surrogate-based optimization of tidal turbine arrays: a case study for the Faro-Olhão inletPublication . G-Gorbeña, Eduardo; Pacheco, André; Plomaritis, Theocharis; Ferreira, Oscar; Sequeira, Claudia; Moura, TheoThis paper presents a study for estimating the size of a tidal turbine array for the Faro-Olhão Inlet (Potugal) using a surrogate optimization approach. The method compromises problem formulation, hydro-morphodynamic modelling, surrogate construction and validation, and constraint optimization. A total of 26 surrogates were built using linear RBFs as a function of two design variables: number of rows in the array and Tidal Energy Converters (TECs) per row. Surrogates describe array performance and environmental effects associated with hydrodynamic and morphological aspects of the multi inlet lagoon. After validation, surrogate models were used to formulate a constraint optimization model. Results evidence that the largest array size that satisfies performance and environmental constraints is made of 3 rows and 10 TECs per row.
- Impacts of human interventions on the evolution of the Ria Formosa barrier island system (S. Portugal)Publication . Kombiadou, Katerina; Matias, Ana; Ferreira, Oscar; Carrasco, A. Rita; Costas, Susana; Plomaritis, TheocharisHuman interventions on sandy barriers disturb natural barrier dynamics, to the extent of having become key forces in modifying geomorphological evolution. This work identifies natural and human-induced drivers and analyses their importance to the multi-decadal evolution of the Ria Formosa barrier island system, in South Portugal. Aerial photographs from the last six decades and historical maps are used to assess changes in cross-shore rates, morphological characteristics (barrier and dune widths, inlet morphology and migration) and barrier areas, through systematic methods that can be easily transferred to other barrier systems. Interventions, and especially hard engineering ones (jetties, inlet stabilisations), affected barrier evolution trends. Shore-perpendicular works increased shoreline progradation updrift and initiated coastal retreat downdrift, with strongest erosive impacts along the edges of the system. Inlet stabilisations changed tidal inlet hydrodynamics and initiated ebb-shoal attachment to the barriers on either side of a non-migrating inlet that experienced loss of tidal prism. This shoal attachment was the main factor for the increase in total barrier area of Ria Formosa during the 60 years of analysis. Barrier growth after 2005 was slower, which could indicate that the system is reaching morphodynamic stability.
- Process-based indicators to assess storm induced coastal hazardsPublication . Ferreira, Óscar; Plomaritis, Theocharis A.; Costas, SusanaStorms are responsible for several hazards (e.g. overwash, erosion, inundation) in coastal areas, leading to the destruction of property and loss of life in populated areas. Various indicators are used to express potential storm impact and describe the associated hazards. The most commonly used indicators include either forcing parameters (e.g. wave height, sea level) or coastal morphologies (e.g. dune height or berm width). Whereas they do not represent the processes associated with storm induced hazards in coastal areas. Alternatively, a hazard could be better characterised if process-based indicators are used instead. Process-based indicators express the result of the forcing mechanisms acting over the coastal morphology and reflect both hydrodynamic and morphological characteristics. This work discusses and synthesizes the most relevant process-based indicators for sandy shores subject to overwash, erosion and inundation promoted by storms. Those include: overwash depth, potential and extent; shoreline, berm or dune retreat; vertical erosion; and inundation depth and extent. The selection of a reduced set of process-based indicators to identify coastal hazards induced by storms in sandy coasts will facilitate comparison of different coastal behaviours for distinct storm return periods, and help to optimise coastal management plans, thereby contributing to the reduction of coastal risks.
- Contribution of storms to shoreline changes in mesotidal dissipative beaches: case study in the Gulf of Cadiz (SW Spain)Publication . Puig, Maria; Del Rio, Laura; Plomaritis, Theocharis A.; Benavente, JavierIn this study an analysis of storminess and rates of shoreline change is performed and discussed jointly in four geomorphological units of the Gulf of Cadiz (SW Spain) for the period of 1956-2010. For this purpose, storm events are identified based on the following characteristics: wave height above 2.5 m, a minimum duration of 12 h and events with calm periods of less than 24 h were considered as a single event. Subsequently, energy parameters are determined in order to characterize storm-induced impacts. Conversely, geographic information system (GIS) tools are used to measure shoreline changes in aerial photographs and orthophotographs of each site, selecting the high water line as shoreline proxy. Each geomorphological unit is divided into different behavioural patterns according to recorded coastal changes, so that each one shows a particular behaviour.In general the variability of shoreline changes that is explained by storms and the relation between storm parameters and coastal changes present better results in exposed areas (Cadiz and Vistahermosa) than in sheltered areas (Valdelagrana spit barrier) because the former are more sensitive to storm impacts. On the contrary, in areas where there is no relation between coastal changes and storm parameters (Valdelagrana and Sancti Petri sand spit), it is suggested that anthropogenic factors are the main forcing agents determining shoreline behaviour. However, in these areas the storminess also modulates coastline recession by increasing erosion when the number of storms is high.
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