a b s t r a c tAn unstructured version of SWAN (Simulating WAves Nearshore) is implemented in the Sea of Iroise (western Europe) to assess the wave energy resource at high spatial resolutions in coastal areas. Numerical results are compared with available measurements of the significant wave height and the peak period at nine locations including (1) long-term offshore observations and (2) medium to short-term data acquired during field campaigns. A medium-term evaluation of the wave energy resource for a eight-years period (2004e2011) is performed exhibiting major nearshore energetic patterns off the isles of Ushant and Sein and in the coastal areas of the bay of Audierne, the Crozon Peninsula and the northern coastline. The variability of wave power production is estimated revealing in accordance with numerical modelling conducted over the European shelf seas significant inter-seasonal and inter-annual evolutions of the resource in the Sea of Iroise. These changes appear particularly noticeable during the winter period with opposite situations in the distribution of monthly average wave energy flux. In the perspective of the implementation of wave energy converters devices, the present assessment is finally exploited to investigate the local distributions of wave energy flux against periods and directions in areas of maximum mean wave power.

Successful deployment of tidal energy converters relies on access to accurate and high resolution numerical assessments of available tidal stream power. However, since suitable tidal stream sites are located in relatively shallow waters of the continental shelf where tidal currents are enhanced, tidal energy converters may experience effects of windgenerated surface-gravity waves. Waves may thus influence tidal currents, and associated kinetic energy, through two non-linear processes: the interaction of wave and current bottom boundary layers, and the generation of wave-induced currents. Here, we develop a three-dimensional tidal circulation model coupled with a phase-averaged wave model to quantify the impact of the waves on the tidal kinetic energy resource of the Fromveur Strait (western Brittany)-a region that has been identified with strong potential for tidal array development. Numerical results are compared with in-situ observations of wave parameters (significant wave height, peak period and mean wave direction) and current amplitude and direction 10 m above the seabed (the assumed technology hub height for this region). The introduction of waves is found to improve predictions of tidal stream power at 10 m above the seabed at the measurement site in the Strait, reducing kinetic energy by up to 9 % during storm conditions. Synoptic effects of wave radiation stresses and enhanced bottom friction are more specifically identified at the scale of the Strait. Waves contribute to a slight increase in the spatial gradient of available mean tidal stream potential between the northwestern area and the southeastern part of the Strait. At the scale of the region within the Strait that has been identified for tidal stream array development, the available mean spring tidal stream potential is furthermore reduced by 12 % during extreme waves conditions. Isolated effects of wave radiation stresses and enhanced bottom friction lead to a reduction in spring tidal potential of 7.8 and 5.3 %, respectively. It is therefore suggested that models used for tidal resource assessment consider the effect of waves in appropriately wave-exposed regions.

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Whereas numerous numerical modelling have been conducted to gain further insights about the hydrodynamic characteristics of tidal stream energy sites, the long-term transport of water particles has been routinely ignored. However, a refined evaluation of circulation pathways is fundamental to assess water-quality changes induced by tidal energy converters. The present study investigates the tide-induced Lagrangian circulation in north-western coastal waters of Brittany (France, western Europe), including numerous islands, shoals and straits with strong potential for turbine farm implementation. Particular attention is dedicated to the hydrodynamic impact of tidal stream power extraction from a series of horizontal-axis turbines. An original approach, based on the coupling of the Lagrangian barycentric method with predictions from a model with high spatial resolution, is considered to assess circulation pathways in a single synoptic view. Spatial results reveal a complex Lagrangian circulation highly controlled by bathymetry and islands geometry. The residual flow in the Fromveur Strait, separating Ushant island from Molène archipelago, displays thus a strong asymmetry, between a prominent north-eastern pathway with residual currents up to 0.45 m s −1 and a southward circulation. The positions of cyclonic and anti-cyclonic recirculations, both upstream and downstream the Strait, are furthermore precisely defined. The north eddy is found closely located to the sand bank of the Four. The extraction of tidal stream power impacts mainly the residual Lagrangian circulation along the current stream emerging from the Strait, with a tendency for surrounding eddies to get closer to the tidal stream energy site. The displacements of the south and north recirculations may thus exceed 1.5 km with possible implications on the evolution of surrounding seabed features.

Locations of wave energy converters (WECs) are, most of the time, determined in areas with the highest density of mean wave power while ignoring the temporal variabilities of the resource. The most energetic regions are, however, characterised by strong interand intra-annual variations of wave power that may impact the energy production and performances of devices. We investigated these influences by focusing on the generated power from three well-known WECs that reached the stage of full-stage testing: Pelamis, AquaBuOY and Wave Dragon. This evaluation was conducted in western Brittany, one of the most energetic area along the coast of France. In comparison with the available resource, the generated technical power was characterised by reduced annual and seasonal variations. These effects were particularly noticeable for Pelamis that exhibited a reduced intermittency in the energy output between the winter and summer periods. The most energetic conditions had furthermore a restricted contribution to devices power output, mainly related to events with energy periods between 10.5 and 12.5 s, and significant wave heights between 2.75 and 4.25 m. WECs performances exhibited finally strong variabilities, in winter, with monthly-averaged values of the capacity factor up to 65% for Wave Dragon.