Resumo

NEVES, Diogo Ruben et al. Risk assessment methodology for the overtopping of maritime structures: application to the port and bay of Praia da Vitória, Azores, Portugal. RGCI [online]. 2012, vol.12, n.3, pp.291-312. ISSN 1646-8872.

The present work describes the methodology developed to assess the overtopping risk of port and coastal structures that was implemented on GUIOMAR, an integrated decision support system for port and coastal management, developed by the National Laboratory for Civil Engineering (LNEC), Portugal, whose focus is to prevent and support the management of emergency situations and the long-term planning of interventions in the study area. The incident wave climate and the corresponding mean overtopping discharges per unit length of the crest of the studied structure are the basis of the above referred methodology. The sea state determination is performed by coupling numerical wave propagation models using input wave data from wave-buoys or regional forecast wave models. The overtopping calculation is carried out with the NN_OVERTOPPING2 tool, which is based on neural network modelling. This tool was developed as part of the European project CLASH to predict Froude-scaled mean wave overtopping discharges, q, and the associated confidence intervals for a wide range of coastal structure types (such as dikes, rubble mound breakwaters, and caisson structures). In addition, prototype mean overtopping estimations, allowing for scale and model effects, are provided. The presented overtopping risk assessment methodology is based on four major steps: (i) the determination of wave overtopping over the studied structure considering the incident sea waves in the period between 2009 and 2010; (ii) the determination of the probability of overtopping exceeding pre-determined thresholds and corresponding probability levels; (iii) the establishment of the levels of consequences associated to the occurrence of overtopping that exceeds those thresholds; (iv) the combination of the above steps to assess overtopping risk levels. Once obtained the risk level, it is possible to plot it on a map, as well as the acceptability level of that risk in each studied zone or structure. This information is crucial for the management of long-term interventions on port and coastal areas. The methodology was tested for three different structure cross-sections of the port and bay of Praia da Vitória, at Terceira Island, Azores: the cross-section of the south breakwater that directly protects the dock 12 of the port, the cross-section of the seawall directly in front of the entrance of the bay of Praia da Vitória and the cross-section of the root of an existing groyne in the same area. In all studied sections, the risk of overtopping caused by the incident sea waves was characterized for the two-year period between 2009 and 2010. The presented methodology proved to be simple and effective enabling the easy extension to other types of risk (navigation, floods). Moreover, the methodology implemented on the GUIOMAR system is a step forward and a valuable contribution to make a more robust and effective support to the port and coastal management.

Palavras-chave : Risk Assessment; GUIOMAR; Wave propagation; Neural network models.

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