Resumo

PEREIRA, Rui China; PINTO, F. Taveira; SILVA, Raquel  e  NEVES, Luciana das. Experimental evaluation of the influence of detached breakwater head configuration in the morphological behavior of the adjacent beach. RGCI [online]. 2013, vol.13, n.3, pp.301-316. ISSN 1646-8872.  https://doi.org/10.5894/rgci398.

The Atlantic coast of Portugal is exposed to rough wave climate conditions and frequently submitted to powerful storms, endangering waterfronts, infrastructures and natural landscapes. Due to the social, environmental and economic significance of these areas to the local communities and to the national progress, measures must be taken by the decision-makers to control and reduce the negative impacts from the wave action. In order to define effective plans, it is important that technical and scientific aspects of the natural processes are understand, as well as the impacts of the proposed solutions. The planning, the design and the construction processes of a coastal structure depend on the characteristics and potential of the available equipment and of the construction methods applied. Over the years, new instruments and innovative techniques, allow the conception of new solutions, in order to adapt traditional interventions to the present demands. In this context, the detached breakwaters are known as structures that not only provide shelter from the waves, inducing the wave energy reduction, but that can also improve bathing conditions and local habitats adaptation. A detached breakwater can, in general terms, be described as a coastal structure, built inside/near the surf zone, having an approximate orientation parallel to the coast. Due to its relative position to the coastline, the structure interferes with the normal wave propagation, reducing wave height and wave energy in the lee zone. During the design process of these structures, it is important to consider the wave-structure interaction, defined by their functional parameters (e.g.: length, orientation and distance to the shoreline), that establish their efficiency. Aiming to evaluate the efficiency of detached breakwaters as coastal defence structures in the west coast of Portugal, a series of studies was initiated in the Hydraulics, Water Resources and Environment Division (SHRHA), of the Civil Engineering Department (DEC), of Faculty of Engineering, University of Porto (FEUP). Firstly, a detached breakwater was proposed for the defence of the urban front of Espinho, located on the northwest coast of Portugal. Following this study, numerical simulation of the hydrodynamic and the morphodynamic conditions were performed. The present situation was compared with a scenario of implantation of the proposed breakwater. Simulation results suggested the need to test different configurations for the detached breakwater. This way, the physical modelling research study, here described, was conducted in order to analyse the effect of different configurations of, coastline parallel, detached structures in the adjacent coastline/beach. Specifically, the influence of three different configurations for the head of a detached breakwater, when subjected to two wave conditions typical of the west coast of Portugal, was tested in a movable bed physical model. In the experimental tests, no significant differences were observed in the sediment transport patterns surrounding the structure. The transported sand was removed from lateral strips, being deposited in the breakwater lee, along the central axis of the model. The total volume of sand of the beach was maintained. The occurrence of overtopping in some of the tests, with higher significant wave heights, imbalances the recirculation currents patterns in the lee of the structure, reducing the expression of the registered changes. The results showed that the conical configuration of the breakwater head, with lower slopes, has a positive effect in terms of the overall stability of the structure and minimizes localized erosion in the breakwater toe.

Palavras-chave : Detached Breakwater; Physical Modelling; Morphological Evolution; Coastline; Hydraulics Laboratory of FEUP.

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