Coastal defence works, such as breakwaters, are structures that aim to support the action of waves and dissipate their energy. Therefore, they provide conditions for stabilizing the coast, protecting ports, beaches and other coastal infrastructures and ecosystems. Semicircular breakwaters have been applied in different locations around the world due to their aesthetic advantages and high structural performance. Marine structures are subject to hydrodynamic actions normally estimated through physical models. However, these models are complex to implement, involving high costs and long experimental procedures. Thus, alternative methodologies for studying the hydrodynamic performance of these structures are of great use. This work presents the results of the application of a computational fluid dynamics (CFD) tool to study the stability of a perforated semicircular breakwater, based on a rubble mound foundation. The model was validated against experimental results of the critical weight necessary to resist sliding, taking into account the effects of water depth and different characteristics of the waves. A comparison is made between the perforated and the non-perforated solution in terms of the breakwater’s performance to dissipate wave energy. Dissipation conditions of this energy, in the exposed face, are also evaluated in detail, in order to assess the potential of this structure as a biological refuge for marine species. Both solutions show similar performance in terms of results obtained for the wave reflectivity coefficient. The turbulence dissipation on the exposed face of the perforated breakwater is limited to a region of restricted extension around it, which is advantageous in terms of the passage of species into the breakwater.

In the current context of climate change, understanding the effects of the changing conditions on estuaries is of utmost importance to protect populations and ecosystems. Given the diversity of impacts depending on the region, there is a need for local and dedicated studies to understand and mitigate the risks. Numerical models can provide forecasts of extreme floods and sea-level rise (SLR). However, they can present inaccuracies. In this work, the ensemble technique was applied to improve the numerical modeling forecasting for estuaries by considering scenarios of extreme river flow discharges (EFDs) and SLR scenarios for 2050 and 2100. The simulations were performed for two different estuarine regions in northern Portugal, and the superensemble was constructed with the results of two different numerical models. The results differed per estuary, highlighting the importance of a local approach. For the Douro estuary dynamics, the results showed that for the EFD, the effects of the SLR were not noticeable, indicating that, in this estuary, the river component was more important than the maritime component. In contrast, the Minho estuary dynamics were found to be affected by the SLR along the whole estuarine region, indicating a maritime influence and a worsening of the flood conditions for future scenarios.

O fenómeno da erosão costeira afeta profundamente a costa portuguesa. O sistema praia-oceano não se pode considerar em situação de equilíbrio morfodinâmico, porque as praias são sistemas abertos, sendo os seus sedimentos constantemente transportados. Os ventos, marés e agitação marinha são os principais agentes erosivos, mas existem outras causas de origem antrópica que influenciam os processos erosivos. Este trabalho tem como objetivo avaliar as alterações morfológicas de muito curto termo em diferentes estados de agitação e tipologia de maré, na praia de Ofir, situada na costa NO Portuguesa. Esta praia foi intervencionada com cilindros geossintéticos como medida de defesa costeira. O trabalho é baseado num programa de monitorização, recorrendo a levantamentos topográficos de alta precisão com auxílio de equipamento DGPS. A aplicação de cilindros geossintéticos nesta praia revelou-se eficiente no período analisado e nas condições de agitação e maré verificadas, embora tenham sofrido erosão ficando expostos. CHARACTERIZATION OF BEACH MORPHODYNAMICS UNDER THE INFLUENCE OF GEOSYNTHETIC CYLINDERS: OFIRBEACH, PORTUGAL, CASE STUDYABSTRACT The phenomenon of coastal erosion deeply affects the Portuguese coast. The beach-ocean system cannot be considered in a situation of morphodynamic balance because the beaches are open systems, and their sediments are being constantly transported. Winds, tides and waves are the main erosive actions, but there are other causes of anthropogenic origin that influence erosional processes. This work aims to evaluate the morphological changes of short time scale, considering different waves and tide conditions at Ofir beach, located at the NW Portuguese coast. This beach was intervened with geosynthetic cylinders as a coastal defense measure. The work is based on a monitoring program, using high-precision topographic surveys with DGPS equipment. The application of geosynthetic cylinders on this beach proved to be efficient in the analyzed period and in the verified conditions of waves and tides, although they have suffered erosion and have been exposed.

REVISTA NUCLEUS - ISSN 1982-2278(ISSN 1678-6602-formato impresso) é uma publicação semestral da FUNDAÇÃO EDUCACIONAL DE ITUVERAVA multidisciplinar; print ISSN 1678-6602; ISSN on-line 1982.2278; DOI 10.3738/1982.2278