Protection of gravel-dominated coasts through wave farms: Layout and shoreline evolution

The Potential of Wave Energy Conversion to Mitigate Coastal Erosion from Hurricanes

Wave energy conversion technologies have recently attracted more attention as part of global efforts to replace fossil fuels with renewable energy resources. While ocean waves can provide renewable energy, they can also be destructive to coastal areas that are often densely populated and vulnerable to coastal erosion. There have been a variety of efforts to mitigate the impacts of wave- and storm-induced erosion; however, they are either temporary solutions or approaches that are not able to adapt to a changing climate. This study explores a green and sustainable approach to mitigating coastal erosion from hurricanes through wave energy conversion. A barrier island, Dauphin Island, off the coast of Alabama, is used as a test case. The potential use of wave energy converter farms to mitigate erosion due to hurricane storm surges while simultaneously generating renewable energy is explored through simulations that are forced with storm data using the XBeach model. It is shown that wave farms can impact coastal morphodynamics and have the potential to reduce dune and beach erosion, predominantly in the western portion of the island. The capacity of wave farms to influence coastal morphodynamics varies with the storm intensity.

Wave energy assessment under climate change through artificial intelligence

The implementation of renewable energies is among the main challenges that we are confronting in the present situation of climate change. In this work, an artificial neural network (ANN) is optimized and used to assess the wave energy resource available to a wave farm over its service life. We select as case study a stretch of coastline in southern Spain. Different ANN architectures and training algorithms are tested for a dataset in deep water composed by: three values of significant wave height, four values of peak period, two values of incoming wave direction, three astronomical tide values, three storm surge values and three values of sea level rise induced by climate change. These deep-water sea states were propagated using a numerical model (Delft3D-Wave) and results were obtained at 176 locations. Thus, more than 114,000 data were used to train and test the ANNs. Once validated, the ANN was used to assess the cumulative wave energy at 704 locations during a 25-year period for three scenarios of rise in sea level according to the Intergovernmental Panel on Climate Change (IPCC) reports: present situation, pessimistic IPCC projection and optimistic IPCC projection. According to the results, the cumulative wave energy in the case study increases with increasing water depths. The greatest values of cumulative wave energy are reached at great depths off a shoreline horn and a port. Importantly, the rise in sea level will induce an increase in the wave energy resource. The ANN developed in this work allows the quantification of wave energy over long-term periods, reducing the computational cost, as well as the choice of the best locations for wave farms considering the effects of climate change.

Multi-criteria characterization and mapping of coastal cliff environments: A case study in NW Spain

This paper presents a novel approach to characterize cliff exposure to marine action that combines wave power and biology. This multidisciplinary approach is illustrated through a case study on a coastal stretch in NW Spain - the Catedrales Natural Monument. The engineering perspective is based on quantifying the wave power acting on the cliff. To this end, a statistical characterization of the wave climate in deep water is carried out, and relevant sea states are propagated numerically from deep water to the cliff. Four levels of cliff exposure, from sheltered to exposed, are defined based on wave power and mapped onto the study area. As for the biological perspective, ecological factors, bioindicated variables and biological indicators characterized through field observations are considered and, on this basis, also four levels of cliff exposure are established and mapped. In general, there is good agreement between the exposure patterns obtained through the engineering and biological perspectives; however, there are some differences in certain areas. The upshot is that the engineering and biological points of view should be regarded as complementary. The multi-criteria characterization performed in this paper may be used as a management tool to establish different degrees of exposure to marine action on cliff coasts elsewhere.

Coastal infrastructure operativity against flooding - A methodology

The operativity of the transport infrastructures and urban developments protected by coastal structures is conditioned by flooding events and the resulting wave overtopping. This work presents a methodology to assess the operational conditions of infrastructures located in coastal areas based on the combination of advanced statistical techniques, laboratory experiments and state-of-the-art numerical models properly validated. It is applied to a case study in the SW coast of England, the railway seawall at Dawlish, which was subjected to recurrent wave overtopping until its dramatic collapse in February 2014. To quantify the increase in overtopping discharges with wave height and water level, we define an ad hoc variable, the effective overtopping forcing, which explains 98% of the variability of the overtopping discharge. The return periods associated to the operational thresholds for coastal structures protecting people and railways are also obtained. The proposed methodology enables the assessment of the overtopping discharge induced by a given sea state and, thus, check if a coastal infrastructure will be or not operational under any expected marine condition. This innovative methodology can also be used to analyse the flooding event consequences on urban areas protected by coastal infrastructures.

The impacts of wave energy conversion on coastal morphodynamics

In recent decades, utilization of renewable energy resources, including ocean waves, has been promoted as part of a global effort to transition away from the use of fossil fuels. This is largely due to the accompanying greenhouse gas emissions and its catastrophic impacts on the environment, which are expected to worsen with the changing climate. Energy from ocean waves can be harnessed and converted into electricity with devices referred to as wave energy converters (WECs). Many researchers have studied the impacts of the WECs on coastal hydrodynamics, however, the impact on morphodynamics is not as well understood. In this paper, we review studies that assess the impacts of wave farms on coastal erosion. The results of a number of studies that focus on various locations around the world show that WECs often generate clean and renewable energy without negatively impacting local coastlines, and in fact often mitigate coastal erosion.

Wave energy converter geometry for coastal flooding mitigation

Wave farms, i.e., arrays of wave energy converters (WECs), have been proposed to fulfil the dual function of carbon-free energy generation and coastal protection. The objective of this work is to investigate, for the first time, how the coastal protection performance against flooding is affected by WEC geometry. This is done by means of a case study with WaveCat WECs (floating, overtopping WECs) deployed off the Playa Granada beach (Spain). To this end, two models of WaveCat WECs with different geometries are tested in a laboratory tank at a 1:30 scale under low-, mid- and high-energy sea states representative of the wave conditions of Playa Granada. The geometries differed in the angle between the twin hulls (wedge angle) of WaveCat: 30° and 60°. The reflection and transmission coefficients thus obtained are used in a coupled numerical modelling approach, combining wave and coastal processes models (SWAN and XBeach-G, respectively). We find that WECs with an angle of 60° provide more (less) protection for long (short) wave periods in terms of reductions in wave height and run-up on the beach. As for the flooded dry beach areas, they are generally smaller for WECs with 60°, with only some exceptions under mild conditions. Thus, considering that beach inundation usually occurs under high-energy, storm conditions, we conclude that the wave farm composed by WECs with a wedge angle of 60° is more efficient against coastal flooding.

Wave farm impacts on coastal flooding under sea-level rise: A case study in southern Spain

Coastal flooding, already an acute problem in many parts of the world, will be exacerbated in the near future by the sea level rise induced by climate change. The influence of wave farms, i.e., arrays of wave energy converters, on coastal processes, in particular sediment transport patterns, has been analysed in recent works; however, their influence on coastal flooding has not been addressed so far. The objective of this work is to investigate whether a wave farm can provide some protection from flooding on the coast in its lee through a case study: a gravel-dominated beach in southern Spain (Playa Granada). We consider three sea-level rise (SLR) scenarios: the present situation (SLR0), an optimistic projection (SLR1) and a pessimistic projection (SLR2). Two state-of-the-art numerical models, SWAN and XBeach-G, are applied to determine the wave propagation patterns, total run-up and flooded dry beach area. The results indicate that the absorption of wave power by the wave farm affects wave propagation in its lee and, in particular, wave heights, with alongshore-averaged reductions in breaking wave heights about 10% (25%) under westerly (easterly) storms. These lower significant wave heights, in turn, result in alongshore-averaged run-up reductions for the three scenarios, which decreases with increasing SLR values from 5.9% (6.8%) to 1.5% (5.1%) for western (eastern) storms. Importantly, the dry beach area flooded under westerly (easterly) storms is also reduced by 5.7% (3.2%), 3.3% (4.9%) and 1.99% (4.5%) in scenarios SLR0, SLR1 and SLR2, respectively. These findings prove that a wave farm can actually reduce coastal flooding on its leeward coast.

Numerical Simulations of the Hydraulic Performance of a Breakwater-Integrated Overtopping Wave Energy Converter

OBREC is the acronym that stands for Overtopping Breakwater for Energy Conversion. It is a multifunctional device aimed to produce energy from the waves, while keeping the harbour area protected from flooding. In this paper, the inclusions of a berm to reduce wave reflection, the shape of the sloping plate to maximise wave overtopping and the reservoir width and the crown wall shape to maximise wave energy capture while keeping the harbour safety were analysed to optimize the hydraulic and structural performances of the device. Several configurations were numerically investigated by means of a 2DV RANS-VOF code to extend the results already obtained during previous experimental campaigns. The wave reflection coefficient, the average wave overtopping flows and the wave loadings along the structure are computed, compared with existing formulae and discussed with reference to the OBREC prototype installed in the Port of Naples.

Dual wave farms and coastline dynamics: The role of inter-device spacing

In dual wave farms, i.e., arrays of wave energy converters (WECs) with a dual function - generation of renewable power and mitigation of coastal erosion - the spacing between the WECs is a fundamental design parameter. The present research has the objective of establishing how this parameter affects the shoreline evolution behind the array and, on this basis, to propose and apply a method to determine the optimum spacing for coastal protection. The method is demonstrated on a beach subjected to severe erosion. Five case studies are considered: four with different inter-WEC spacings, and one without the wave farm (baseline). A spectral wave propagation model is applied to analyse the variations in significant wave height behind the WEC array. Longshore sediment transport rates are calculated, and a shoreline model is applied. We find that in all the case studies the dry beach area is greater than in the baseline (no farm) case study, which proves the capacity of the dual WEC array to mitigate the erosive trends of the system. Importantly, we obtain that the inter-WEC spacing plays a fundamental role in the evolution of the shoreline and, consequently, in the effectiveness of the WEC array for coastal protection. The case studies with intermediate spacings yield the best performance in terms of dry beach area. More generally, the benefits of dual wave farms in terms of protection of coastal properties and infrastructure, and the ensuing savings in conventional coastal defence measures (coastal structures, beach nourishment, etc.) contribute to the development of wave energy by enhancing its economic viability. The methodology presented in this paper can be used to optimize the design of dual wave farms elsewhere.

Wave farm effects on the coast: The alongshore position

For wave energy to become a fully-fledged renewable and thus contribute to the much-needed decarbonisation of the energy mix, the effects of wave farms (arrays of wave energy converters) on coastal systems must be addressed. The objective of this work is to investigate the effects of wave farms on the longshore sediment transport and shoreline evolution of a gravel-dominated beach and, in particular, its sensitivity to the longshore position of the farm based on eight scenarios. Nearshore wave propagation patterns are computed by means of a spectral wave propagation model (SWAN), variations in sediment transport rates induced by the farm are calculated, and a one-line model is applied to determine the shoreline position and dry beach area. The significant wave height at breaking is reduced in the lee of the wave farm, dampening sediment transport. We find that changes in the dry beach area induced by the wave farm are highly sensitive to its alongshore position, and may result in: (i) erosion relative to the baseline scenario (without wave farm) in three of the eight scenarios, (ii) accretion in three other scenarios, and (iii) negligible effects in the remaining two. These results prove that the alongshore position of the wave farm controls the response of the beach to the extent that it may shift from accretionary to erosionary, and provide evidence of its effectiveness in countering erosion if appropriately positioned. This effectiveness opens up the possibility of using wave farms not only to generate carbon-free energy but also to manage coastal erosion, thus strengthening the case for the development of wave energy.