Coastal areas accommodate a great part of large metropolises as they support a great amount of economic and leisure activities. The attraction of people to coastal zones is contributing to an intense and continuous urbanization of these areas, while the ecosystems are threatened by the increase of natural extreme weather events (e.g., intensity and duration of storms, floods), which interfere with local wave climate and changes in morphological beach characteristics. Protection of coastal zones predisposed to coastline recession, due to the action of high tides, high sediment transport deficit, and high wave energy, may involve various coastal structures to reduce or at least to mitigate coastal erosion problems. Many of the current coastal protections (notably groins, seawalls, and emerged breakwaters) were built with a single purpose, which was to protect at all costs without environmental or economic concerns, especially maintenance costs, or the negative consequences that such structures could cause up to considerable distances along the coast. The current concept of integrated coastal zone management presupposes studies involving other types of concerns and more actors in the decision-making process for the implementation of coastal works. In this context, multifunctional structures emerge and are increasingly frequent, such as the so-called multifunctional artificial reefs (MFARs), with the aim of improving leisure, fishing, diving, and other sporting activities, in addition to coastal protection. MFARs are in fact one of the latest concepts for coastal protection. Behind the search for more efficient and sustainable strategies to deal with coastal retreat, this study focused on a comparison between the performance of two traditional coastal protection solutions (submerged detached breakwater and emerged detached breakwater) and an MFAR on a particular coastal stretch. In order to analyse the hydro- (wave height and wave energy dissipation) and morphodynamics (sediment accumulation and erosion areas, and bed level) of the structures and beach interactions, two numerical models were used: SWAN (Simulation WAves Nearshore) for hydrodynamics and XBeach for hydrodynamics and morphodynamics. In addition, a comparison between SWAN and XBeach hydrodynamic results was also performed. From the simulations conducted by SWAN and XBeach, it can be concluded that amongst all structures, the emerged detached breakwater was the most efficient in reducing significant wave heights at a larger scale due to the fact that it constituted a higher obstacle to the incoming waves, and that, regarding both submerged structures (detached breakwater and the MFAR), the MFAR presented a more substantial shadow zone. Regarding morphodynamics, the obtained results presented favourable tendencies to sediment accretion near the shoreline, as well as at the inward areas for the three structures, especially for the emerged detached breakwater and for the MFAR in both wave directions. However, for the west wave direction, along the shoreline, substantial erosion was observed for both structures with more noticeable values for the emerged detached breakwater. For all the northwest wave direction scenarios, no noticeable erosion areas were visible along the shoreline. Overall, considering the balance of erosion and accretion rates, it can be concluded that for both wave predominance, the submerged detached breakwater and the MFAR presented better solutions regarding morphodynamics. The MFAR storm wave condition performed in XBeach indicated substantial erosion areas located around the structure, which added substantial changes in the bed level.

Extreme wave value analysis under uncertainty scenarios was developed to estimate wave climate characteristics at 17 stations in southwestern European coast off the Iberian Peninsula. A comprehensive wave dataset downscaled with the Wave Watch III (WWIII) model by Meteogalicia under MarRisk Project was used considering results of models from the Coupled Model Intercomparison Project 5 (CMIP5). Descriptive statistics for significant wave height (Hs), peak wave period (Tp), and mean and peak wave direction were performed for historical data (1960−2005), and for projected data in two twenty-year time periods under two Representative Concentration Pathway (RCP) scenarios (2026−2045 and 2081−2100). Hs and Tp extreme values for the study area were obtained using the Gumbel, Fréchet and Weibull probability distributions for the 10-, 50-, and 100-year return period. Obtained results showed that: historical Hs values decrease from North to South and are higher than those calculated in any of the RCPs future scenarios; mean Tp values appear to be constant in all stations; and means for peak and mean direction have higher frequency of occurrence in Q4 (270°−360°). This study also allowed the computation of Hs and Tp values for 100-year return period, which can be used as design criteria for structural analyses in maritime works.

Coastal zone protection is a very crucial issue in order to defend populations and infrastructures as well as to environment conservation. Adequate tools must be tested and implemented for supporting engineering solutions to face this challenge. In this study, 1DH and 2DH models were applied to simulate wave hydrodynamics at Ofir beach, NW Portugal. For this purpose, COULWAVE (1DH) and BOUSS-2D (2DH) models were implemented considering both the presence of a detached breakwater and natural conditions aiming the study of the impact of these structures on the significant wave height and the wave energy. A comparison of the performance of the two models was also developed. The methodology adopted in this research work, where a generalised methodology of models applications was used, allows its replication to other coastal stretches being this application dependent on local environmental conditions.

The construction of harbor defense structures changes the natural sedimentary fluxes that contribute to feed the coastal drift in the adjacent beaches, in many harbors of the world located at river mouths. This paper presents a numerical modelling work, based on the Delft3D software, to study morphodynamics at the river Lima estuary, Portugal. This model was implemented recurring to a hydroinformatic environment that was constructed at University of Minho along the last two decades. Considering specific hydrodynamic conditions and typical characteristics of the estuarine sediments, the capacity of hypothetical structures to improve transport of sediments to the coast was assessed: (i) a submerged transverse non-erodible dam and (ii) an emerged groin linked to the left embankment located at the upstream section of the harbor. The implemented hydroinformatic environment presents capacities to simulate the complex morphodynamic behavior of river mouths. The preliminary results reveals that the proposed structures can have a positive impact throughout dredging works facilitation by transferring depositional areas during flood events to a location near the coast inside the harbor. Ongoing field acquisition data will be essential to validate depositional patterns under different river discharges and wave conditions.

Coastal areas are an apprized environment by society that will continue to expand rapidly. Traditional coastal protection structures are commonly deployed to protect coastal areas endangered by natural extreme weather events. However, due to their limited efficiency and very high costs, more efficient and sustainable strategies to deal with coastal erosion are imperative. This research work focuses on the assessment of engineering solutions to mitigate and delay coastal erosion. Three different structure geometries (triangular prism shape, single detached breakwater and group of two detached breakwaters) are analysed on a realistic bathymetry, using a combination of numerical models (SWAN and XBeach) to study the influence of those structures on the coastal hydro-and morphodynamics. SWAN was used for hydrodynamics and XBeach for hydrodynamics and morphodynamics assessments. In addition, a comparison between SWAN and XBeach hydrodynamics results was also performed. Structures considered in this study have regular shaped geometries, and are characterized in terms of their efficiency regarding wave height and wave energy dissipation considering different wave regimes and performance in terms of longterm beach morphodynamic impact (sediments accumulation and erosion). The analysis is concentrated in two scenarios, one for low and the other for highly energetic hydrodynamics (the most challenging to coastal zones defence). The obtained results allowed classifying their performance in terms of the impact on wave energy and wave height dissipation, and sediment erosion/deposition patterns.