• Energy Research

Introduction: The Danube Delta coast is part of the Danube Delta Biosphere Reserve, thus being aimed to preserve its typical natural habitats. Over the last decades, human interventions along the Danube River, as well as coastal navigation and harbour protection works on the Romanian coast, have determined the reduction of sediment supply along the Danube Delta coast, which is nowadays affected by erosion on its widest part. Sustainable management plans for the Danube Delta coast include the use of working-with-nature solutions. In this work, the effectiveness of artificial reefs along the Danube Delta coast has been assessed, from the hydrodynamic point of view.Methods: The results of a previous wave climate study and a wave model have been used for this purpose. Simulations have been performed for different setup of artificial reefs, with different heights, and for extreme storms with various return periods, to test their effectiveness in reducing wave height and energy. Sea level rise has also been taken into account.Results: Our results show that artificial reefs are significantly effective in reducing the wave heights along the Danube Delta coast.Discussion: However, further detailed analysis concerning the impact of such a coastal protection solution is still needed, especially on the shoreline evolution and the local hydrodynamics.

This paper deals with the question of how to manage vulnerable coastal systems so as to make them sustainable under present and future climates. This is interpreted in terms of the coastal functionality, mainly natural services and support for socio-economic activities. From here we discuss how to adapt for long term trends and for short terms episodic events using the DPSIR framework. The analysis is presented for coastal archetypes from Spain, Ireland and Romania, sweeping a range of meteo-oceanographic and socio-economic pressures, resulting in a wide range of fluxes among them those related to sediment. The analysis emphasizes the variables that provide a higher level of robustness. That means mean sea level for physical factors and population density for human factors. For each of the studied cases high and low sustainability practices, based on stakeholders preferences, are considered and discussed. This allows proposing alternatives and carrying out an integrated assessment in the last section of the paper. This assessment permits building a sequence of interventions called adaptation pathway that enhances the natural resilience of the studied coastal systems and therefore increases their sustainability under present and future conditions.

An analysis of the probability of failure of beaches along the Catalan coast (Northwestern Mediterranean) is presented. The failure condition is defined when waves are able to overtop the beach and reach the backshore. The analysis is performed by means of a verification equation where most of the related variables are assumed to be stochastic. The probability of failure of beaches is calculated by means of MonteCarlo simulations for present conditions and different climate change scenarios. At present 14% of the Catalan beaches fail the proposed protection function against storms. Under a high-end climate change projection (A1FI) 21% of beaches will fail.

The presence of seagrass along the Romanian coast is currently seen as an important component of the marine ecosystem. Moreover, seagrass meadows play an additional wave energy dissipation role that has also to be considered among other ecosystem services. Assessing the impact of a seagrass meadow on the local hydrodynamics is needed to present an integrated protection and adaption plan for discussion with local stakeholders and coastal managers. The impact on wave heights of a possible seagrass meadow, located in front of the barrier beach at the Mangalia marsh on the southern Romanian coast, has been analysed using numerical modelling. Several seagrass configurations have been studied, for low and average wave conditions from various directions. The same waves were used after adding a vegetation mask to the analysed domain, to simulate the presence of a seagrass meadow. The results of the numerical simulations were extracted in several output points, located along three transects crossing the vegetation mask. They show the most significant reduction in the calculated wave energy density during a year of 16.6%, occurring within the seagrass meadow. Our results suggest that, for the southern Romanian coast, seagrass could be introduced in coastal protection plans as an additional measure for wave attenuation. The idea of this work came up following the FP7 RISES-AM project, GA 603396, funded by the FP7-ENV-2013-two stage program of the European Commission. The first author acknowledges the mobility projects MC2017-1274 and MC2018-1922, funded by the Romanian Authority for Scientific Research, covering the expenses of two research visits at the Maritime Engineering Laboratory of the Polytechnic University of Catalonia Barcelona Tech (LIM-UPC), during which work on this topic started. This work was partially supported by the Spanish Government within the Research, Development and Innovation Program through the grant to ECOPLANTS project (Ref. PID2020-119058RB-I00). The REST-COAST Horizon 2020 Research and Innovation Grant 101037097 has also contributed to finance some of the authors. The rest of the work has been performed within the projects PN 18160103 and PN 19200201, funded by the Ministry of Research, Innovation and Digitization of Romania and H2020 DOORS (EC Grant Agreement 101000518). We acknowledge as well the valuable comments of an anonymous reviewer, which allowed us to significantly improve the manuscript. Peer Reviewed

Episodic coastal hazards associated to sea storms are responsible for sudden and intense changes in coastal morphology. Climate change and local anthropogenic activities such as river regulation and urban growth are raising risk levels in coastal hotspots, like low-lying areas of river deltas. This urges to revise present management strategies to guarantee their future sustainability, demanding a detailed diagnostic of the hazard evolution. In this paper, flooding and erosion under current and future conditions have been assessed at local scale at the urban area of Riumar, a touristic enclave placed at the Ebro Delta (Spain). Process-based models have been used to address the interaction between beach morphology and storm waves, as well as the influence of coastal environment complexity. Storm waves have been propagated with SWAN wave model and have provided the forcings for XBeach, a 2DH hydro-morphodynamic model. Results show that future trends in sea level rise and wave forcing produce non-linear variations of the flooded area and the volume of mobilized sediment resulting from marine storms. In particular, the balance between flooding and sediment transport will shift depending on the relative sea level. Wave induced flooding and long-shore sand transport seem to be diminished in the future, whereas static sea level flooding and cross-shore sediment transport are exacerbated. Therefore, the characterization of tipping points in the coastal response can help to develop robust and adaptive plans to manage climate change impact in sandy wave dominated coasts with a low-lying hinterland and a complex shoreline morphology.

The characterization of future wave-storms and their relationship to large-scale climate can provide useful information for environmental or urban planning at coastal areas. A hybrid methodology (process-based and statistical) was used to characterize the extreme wave-climate at the northwestern Black Sea. The Simulating WAve Nearshore spectral wave-model was employed to produce wave-climate projections, forced with wind-fields projections for two climate change scenarios: Representative Concentration Pathways (RCPs) 4.5 and 8.5. A non-stationary multivariate statistical model was built, considering significant wave-height and peak-wave-period at the peak of the wave-storm, as well as storm total energy and storm-duration. The climate indices of the North Atlantic Oscillation, East Atlantic Pattern, and Scandinavian Pattern have been used as covariates to link to storminess, wave-storm threshold, and wave-storm components in the statistical model. The results show that, first, under both RCP scenarios, the mean values of significant wave-height and peak-wave-period at the peak of the wave-storm remain fairly constant over the 21st century. Second, the mean value of storm total energy is more markedly increasing in the RCP4.5 scenario than in the RCP8.5 scenario. Third, the mean value of storm-duration is increasing in the RCP4.5 scenario, as opposed to the constant trend in the RCP8.5 scenario. The variance of each wave-storm component increases when the corresponding mean value increases under both RCP scenarios. During the 21st century, the East Atlantic Pattern and changes in its pattern have a special influence on wave-storm conditions. Apart from the individual characteristics of each wave-storm component, wave-storms with both extreme energy and duration can be expected in the 21st century. The dependence between all the wave-storm components is moderate, but grows with time and, in general, the severe emission scenario of RCP8.5 presents less dependence between storm total energy and storm-duration and among wave-storm components.