Coupling hydrological, habitat and water supply indicators to improve the management of environmental flows.

Highly regulated basins have traditionally required management practices to mitigate the negative environmental impacts and ensure human well-being. This paper proposes and assesses environmental and water supply deficit indicators to assist in the management of environmental flows (e-flows). For that, a water allocation model is applied, and hydrological alteration, habitat alteration and water supply indicators are quantified, normalized and integrated into a general basin management indicator. This basin management indicator is analyzed for four management approaches and seven e-flow scenarios in the Júcar River Basin (eastern Spain). Hydrological alteration indicators show a less pronounced alteration in the river sections located upstream of the basin while a higher alteration in the downstream sections. As for the habitat indicators, they experience an improvement compared to the natural regime. Based on the values of the basin management indicator, the best e-flow scenario to adopt in the Júcar River Basin is selected. The indicators proposed in this work are useful for supporting decision-making regarding the planning and management of e-flows in regulated river basins worldwide.

Effects of environmental flows on hydrological alteration and reliability of water demands.

This paper presents a methodology to assess the effects of management strategies of environmental flows on the hydrological alteration of river basins on a daily scale. It comprises the collection and analysis of data, the implementation and calibration of a water allocation model; the computation of the natural flow regime; and the estimation, normalization, and aggregation of hydrological alteration indicators to obtain a global indicator of the hydrological alteration. The methodology was applied to a case study in the Iberian Peninsula: The Orbigo River basin, which belongs to the Duero River basin district. For that, three management scenarios were defined: the current scenario, a scenario without any environmental flow and the scenario with the environmental flows initially projected for the period 2022-2027. These scenarios were modelled with the SIMGES water allocation model, which is calibrated in the study site, and the hydrological alterations in four river stretches with different locations and characteristics were assessed. The implications of each environmental flow scenario on the demand reliabilities were also analysed. The global indicator of hydrological alteration obtained in the projected scenario was greater (better) than those of the other two scenarios, but the reliabilities of the water demands were worse. The methodology proposed in this work can be helpful to design environmental flow regimes considering both the effects on the hydrological alteration and the implication on the water demand reliabilities.

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.

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.

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.

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.

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.

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

The impacts of wave farms (arrays of wave energy converters, or WECs) on the nearshore must be fully understood for wave technology to develop and thus contribute to a sustainable, carbon-free energy mix in the near future. The objective of this work is to investigate the role played by the farm layout on the wave propagation patterns leewards and the implications for longshore sediment transport (LST) and shoreline evolution on a gravel-dominated deltaic coast. Changes in wave propagation in four scenarios, corresponding to as many wave farm layouts, are computed by means of a spectral numerical model (Delft3D-WAVE) under (i) low-energy and storm conditions, and (ii) westerly and easterly waves - the two prevailing wave directions. On this basis, sediment transport rates are computed and changes in the shoreline position assessed using a one-line model. To quantify the impact of the wave farm on the nearshore wave conditions, sediment transport and shoreline, we define three ad hoc indicators: the non-dimensional wave height reduction, the non-dimensional LST rate reduction and the non-dimensional shoreline advance. Significant wave heights decrease in the lee of the wave farm, with the consequent reduction in LST rates. As a result, the dry beach area increases in every scenario under both westerly and easterly waves. We find that case studies with the WECs arranged on fewer rows but covering a greater stretch of coastline provide better coastal protection. These results confirm that wave farms can be used not only to generate carbon-free energy but also to protect gravel-dominated coasts.

An integrated methodology to forecast the efficiency of nourishment strategies in eroding deltas.

Many deltas across the globe are retreating, and nearby beaches are undergoing strong erosion as a result. Among soft and prompt solutions, nourishments are the most heavily used. This paper presents an integrated methodology to forecast the efficiency of nourishment strategies by means of wave climate simulations, wave propagations with downscaling techniques, computation of longshore sediment transport rates and application of the one-line model. It was applied to an eroding deltaic beach (Guadalfeo, southern Spain), where different scenarios as a function of the nourished coastline morphology, input volume and grain size were tested. For that, the evolution of six scenarios of coastline geometry over a two-year period (lifetime of nourishment projects at the study site) was modelled and the uncertainty of the predictions was also quantified through Monte Carlo techniques. For the most efficient coastline shape in terms of gained dry beach area, eight sub-scenarios with different nourished volumes were defined and modelled. The results indicate that an input volume around 460,000m3 is the best strategy since nourished morphologies with higher volumes are more exposed to the prevailing storm directions, inducing less efficient responses. After setting the optimum coastline morphology and input sediment volume, eleven different nourished grain sizes were modelled; the most efficient coastline responses were obtained for sediment sizes greater than 0.01m. The availability of these sizes in the sediment accumulated upstream of a dam in the Guadalfeo River basin allows for the conclusion that this alternative would not only mitigate coastal erosion problems but also sedimentation issues in the reservoir. The methodology proposed in this work is extensible to other coastal areas across the world and can be helpful to support the decision-making process of artificial nourishment projects and other environmental management strategies.

Integrating complex numerical approaches into a user-friendly application for the management of coastal environments.

This paper presents a software platform to compute the total water level, one of the key variables for the environmental management of coastal zones. The platform integrates six modules: (1) simulation of deep-water wave variables, storm surge and river flow; (2) wave downscaling; (3) wave propagation; (4) contribution of the river discharge; (5) astronomical tide; and (6) total water level. It was applied to three case studies in southern Spain. The first case study consisted of designing the extension of a fluvial marina in a highly dynamic area (Guadalete estuary, Cádiz), and the maximum number of floating docks to avoid flooding events was obtained. The second case study involved calculating the operation conditions for navigation purposes in an inlet with sedimentation problems (Punta Umbría, Huelva), and a relationship between the percentage of operation hours and the dredged volume was obtained. The third case study consisted of estimating the number of overwash events as a function of the height of the berm on a deltaic beach with erosion issues (Guadalfeo, Granada), and a simple design curve to help managers during the decision-making process of artificial nourishment projects was provided. These results highlight the potential of the developed software, whose methodology is feasibly extensible to other coastal areas worldwide, to help managers handle a wide range of environmental problems related to the total water level. This is especially relevant due to the expected sea level rise in the coming years.