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

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.

The Expected Impact of Marine Energy Farms Operating in Island Environments with Mild Wave Energy Resources—A Case Study in the Mediterranean Sea

A particularity of island areas is that they are subjected to strong sea state conditions that can have a severe impact on the beach stability, while on the other hand, they rely mainly on diesel combustion for electricity production which in the long run is not a sustainable solution. The aim of this work is to tackle these two issues, by assessing the impact of a hybrid marine energy farm that may operate near the north-western part of Giglio Island in the Mediterranean Sea. As a first step, the most relevant environmental conditions (wind and waves) over a 27-year time interval (January 1992–December 2018) were identified considering data coming from both ERA5 and the European Space Agency Climate Change Initiative for Sea State. An overview of the electricity production was made by considering some offshore wind turbines, the results showing that even during the summertime when there is a peak demand (but low wind resources), the demand can be fully covered by five wind turbines defined each by a rated power of 6 MW. The main objective of this work is to assess the coastal impact induced by a marine energy farm, and for this reason, various layouts obtained by varying the number of lines (one or two) and the distance between the devices were proposed. The modelling system considered has been already calibrated in the target area for this type of study while the selected device is defined by a relatively low absorption property. The dynamics of various wave parameters has been analysed, including significant wave height, but also parameters related to the breaking mechanics, and longshore currents. It was noticed that although the target area is naturally protected by the dominant waves that are coming from the south-western sector, it is possible to occur extreme waves coming from the north-west during the wintertime that can be efficiently attenuated by the presence of the marine energy farm.

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.

Physical Modelling of the Effect on the Wave Field of the WaveCat Wave Energy Converter

The WaveCat is a moored Wave Energy Converter design which uses wave overtopping discharge into a variable v-shaped hull, to generate electricity through low head turbines. Physical model tests of WaveCat WEC were carried out to determine the device reflection, transmission, absorption and capture coefficients based on selected wave conditions. The model scale was 1:30, with hulls of 3 m in length, 0.4 m in height and a freeboard of 0.2 m. Wave gauges monitored the surface elevation at discrete points around the experimental area, and level sensors and flowmeters recorded the amount of water captured and released by the model. Random waves of significant wave height between 0.03 m and 0.12 m and peak wave periods of 0.91 s to 2.37 s at model scale were tested. The wedge angle of the device was set to 60°. A reflection analysis was carried out using a revised three probe method and spectral analysis of the surface elevation to determine the incident, reflected and transmitted energy. The results show that the reflection coefficient is highest (0.79) at low significant wave height and low peak wave period, the transmission coefficient is highest (0.98) at low significant wave height and high peak wave period, and absorption coefficient is highest (0.78) when significant wave height is high and peak wave period is low. The model also shows the highest Capture Width Ratio (0.015) at wavelengths on the order of model length. The results have particular implications for wave energy conversion prediction potential using this design of device.

Rotation, sedimentary deficit and erosion of a trailing spit inside ria of Arousa (NW Spain)

Based on the analysis of a large set of remote images, bathymetric studies and acoustic profiles, we studied the causes of erosion of a small island inside a ria of the NW coast of Spain. The island consists of a rocky sector to the south and a trailing, or comet-tail, spit to the north, which, until 1980, was in an equilibrium between the waves of the open ocean propagated inside the ria and the local wind waves. The development, in the 1970s, of a large park of floating rafts for mussel farming was identified as the factor triggering a period of disequilibrium and severe erosion on the island. The area covered by the floating rafts was the cause of the attenuation of local wind waves and the reinforcement of waves propagated from the open ocean. The spit underwent a period of approximately 38 years of disequilibrium characterized by a rotation movement with several phases. During the first period (1980-1989), a submarine lobe was formed, sequestering approximately 9000 m³ of sediment. Between 1989 and 2015, the spit maintained a rotation of 24° of amplitude and a phase of severe erosion, with rates of up to 6.6 m/yr, began in 2000. Since 2015, the spit has entered a new phase of stabilization, reducing the rotation to a small amplitude of 5°. The rates of erosion have also decreased, although they are still active.

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.

The changing paradigm of coastal management: The Portuguese case

Until the 1980s, the primary goal of coastal works projects was to ensure safety at any cost. This was addressed in an essentially physical manner. Today, concerns are no longer limited to safety; lifestyle and quality of life have become essential components in the successful construction of coastal infrastructure. Other aspects of development have also become important, such as environmental impact, attractiveness and sustainability. New social realities must be addressed, as must the voices of actors and interest groups. The synthesis of recent concerns over coastal public works projects has become increasingly difficult due to new assumptions of value, social acceptance and the sustainability of these projects. In this context, it is now common knowledge that decision-making on a coastal issue should be based on multiple criteria, including technical effectiveness, costs, benefits, implementation and monitoring. Here, coastal issues are reviewed using the dual perspective of meeting current needs and ensuring future sustainability. It is shown that multifunctional facilities built near the coast are one viable solution for managing coastal erosion. The results of a case study conducted in a sensitive area of the Portuguese coast are also presented. Based on an exhaustive review of the literature, it is also shown that improving nautical sports and generating renewable energy should not be neglected. Finally, contemporary adaptation measures and future accommodation options are recommended.

The Expected Shoreline Effect of a Marine Energy Farm Operating Close to Sardinia Island

Coastal areas are defined by numerous opportunities and threats. Among them we can mention emerging renewable projects and on the other hand coastal erosion. In the present work, the impact of a generic wind–wave farm on the nearshore waves and currents in the vicinity of the Porto Ferro inlet (northwest Sardinia) was assessed. Using a reanalysis wave dataset that covers a 40-year interval (1979–2018), the most relevant wave characteristics in the target area were identified. These can reach during winter a maximum value of 7.35 m for the significant wave height. As a next step, considering a modeling system that combines a wave model (simulating waves nearshore (SWAN)) and a surf model, the coastal impact of some generic marine energy farms defined by a transmission coefficient of 25% was assessed. According to the results corresponding to the reference sites and lines defined close to the shore, it becomes obvious that there is a clear attenuation in terms of significant wave heights, and as regards current velocities, although the general tendency for them to decrease, there are, however, some situations when the values of the nearshore current velocities can also decrease. Finally, we can mention that the presence of a marine energy farm seems to be beneficial for the beach stability in this particular coastal environment, and in some cases the transformation of the breaking waves from plunging to spilling is noticed.

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.