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- Beach erosion and recovery during consecutive storms at a steep-sloping, meso-tidal beachPublication . Vousdoukas, Michalis; Almeida, Luis Pedro; Ferreira, ÓscarThis study analyses beach morphological change during six consecutive storms acting on the meso-tidal Faro Beach (south Portugal) between 15 December 2009 and 7 January 2010. Morphological change of the sub-aerial beach profile was monitored through frequent topographic surveys across 11 transects. Measurements of the surf/swash zone dimensions, nearshore bar dynamics, and wave run-up were extracted from time averaged and timestack coastal images, and wave and tidal data were obtained from offshore stations. All the information combined suggests that during consecutive storm events, the antecedent morphological state can initially be the dominant controlling factor of beach response; while the hydrodynamic forcing, and especially the tide and surge levels, become more important during the later stages of a storm period. The dataset also reveals the dynamic nature of steep-sloping beaches, since sub-aerial beach volume reductions up to 30m3/m were followed by intertidal area recovery (–2
- 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.
- Uncertainty analysis related to beach morphology and storm duration for more reliable early warning systems for coastal hazardsPublication . Garzon, Juan L.; Plomaritis, T. A.; Ferreira, OscarEarly warning systems (EWSs) for coastal erosion are highly cost-effective instruments for disaster risk reduction. Among other aspects, an adequate pre-storm beach morphology and the storm characteristic definition are relevant in determining EWSs prediction reliability. Here, XBeach simulations were used to investigate the beach-dune response to different storm events with varying duration and pre-storm morphologies. Severity was defined using wave height return periods (from 5 to 50 years) and duration variability was established by confidence intervals after an adjustment with wave height. Beach morphology variability included different berm morphologies, including erosional and accretional conditions. Three erosion indicators were used: remaining berm width, dune retreat, and eroded volume. Regarding the pre-storm morphology variability: i) pre-storm conditions highly determined the final berm width for the 5 and 10-year events; ii) antecedent morphology affected dune retreat variability mostly for the 50 year events, and; iii) eroded volume depended on the pre-storm conditions, but the percentage of the eroded volume, relative to the initial conditions, was similar regardless of the morphology. Regarding the storm duration effect: i) this variable had a limited impact on the remaining berm width for the 5-year event; ii) storm duration influenced dune retreat mainly for the 50-year event, determining dune breaching occurrence, and; iii) eroded volume response to changes in duration was similar regardless of storm intensity, except for the 50-year event. According to the obtained results, the implementation of reliable EWSs for coastal erosion needs to assess the uncertainties related to initial/forcing conditions, namely pre-storm morphology and storm duration.
- Storm impacts along European coastlines. Part 2: lessons learned from the MICORE projectPublication . Ciavola, Paolo; Ferreira, Óscar; Haerens, Piet; Van Koningsveld, Mark; Armaroli, ClaraThis paper describes the MICORE approach to quantify for nine field sites the crucial storm related physical hazards (hydrodynamic as well as morphodynamic) in support of early warning efforts and emergency response. As a first step historical storms that had a significant morphological impact on a representative number of sensitive European coastal stretches were reviewed and analysed in order to understand storm related morphological changes and how often they occur around Europe. Next, an on-line storm prediction system was set up to enable prediction of storm related hydro- and morphodynamic impacts. The system makes use of existing offthe- shelf models as well as a new open-source morphological model. To validate the models at least one year of fieldwork was done at nine pilot sites. The data was safeguarded and stored for future use in an open database that conforms to the OpenEarth protocols. To translate quantitative model results to useful information for Civil Protection agencies the Frame of Reference approach (Van Koningsveld et al., 2005, 2007) was used to derive Storm Impact Indicators (SIIs) for relevant decision makers. The acquired knowledge is expected to be directly transferred to the civil society trough partnerships with end-users at the end of the MICORE project.
- Why do we decide to live with risk at the coast?Publication . Costas, Susana; Ferreira, Óscar; Martinez, G.Coastal communities have been repeatedly threatened by the ephemeral character of the coast. Morphological changes derived from climate events and sea level oscillations forced the relocation of coastal communities over the past, but never prevented the occupation of this fragile source of wealth. Moreover, the socio-economic impact of high energy events is dramatically increasing due to the growing occupation of the coast, raising the need for rethinking the way disaster risk reduction measures are implemented to ensure effectiveness and acceptance. To illustrate this conflict (occupation versus risk), we explore risk perception in a population located in a fragile segment of the southern coast of Portugal, Praia de Faro, in order to identify the factors shaping risk perception and to understand the reasons behind the occupation of risky coastal areas. The selected community consists of two different populations (a fishermen community and a tourism-related community) sharing the risk associated with storm impacts and coastal retreat. For that, we examine the socio-economic and environmental frameworks and run a set of in depth interviews to provide a frame for understanding the culture of risk in a system with multiple stakeholders and planned measures of relocation. Interviews in Praia de Faro suggest that citizens using the beach as their first residence have voluntarily accepted to live with risk in the beach in exchange for a series of related benefits that they find to largely exceed expected personal damages. Risk perception analysis found that the community is aware about the hazards impacting the area, but they are not worried or prepared to face likely levels of risk derived from the impact of storms estimated by experts. Characteristics of risk perception seem shaped by place attachment, underestimation of impact probability and lessons learnt, and inherent cultural aspects. In addition, it seems clear that imposed measures of relocation are contributing to reduce residents risk perception in an attempt to ensure their permanence in the area in a frame of institutional distrust and absence of genuine communication. Alternative measures to relocation can only exist if responsibilities in risk mitigation are reconsidered and shared.