Directive Cadre sur l’Eau : les pressions anthropiques et leur impact sur les indicateurs de l’état écologique des masses d’eau littorales de la façade Manche-Atlantique. Synthèse bibliographique

Within the European water framework directive (WFD), the status assessment of littoral waters is based both on the chemical quality and on the ecological quality of each water body. Quality elements enabling to assess the ecological status of a water body are, among other things, biological quality elements (phytoplankton, macroalgae, angiosperms, benthic invertebrates, fish), for each of which the member states have developed quantitative indicators. This document is one of the deliverables of a multi-annual study intended to characterize the sensitivity of these biological indicators towards the various anthropogenic pressures exerted on the French Atlantic and Channel coast: ultimately, the goal is to establish a quantitative and predictive relationship, statistically robust, between the WFD indicators used along the French channel and Atlantic coastline, and various anthropogenic pressures acting on these coasts. The aim of the WFD is indeed to restore or maintain a good chemical and biological quality of coastal waters, and thus to limit the impact of human activities potentially responsible for the degradation of ecosystems. This understanding of the linkages and interactions existing between anthropogenic pressures and ecological status of water bodies is therefore essential to identify priorities for action (challenges, substances ...), prioritize actions to implement within restoration programs (technical, fiscal, financial), but also to be able to communicate constructively and persuasively in talks between managers and the various stakeholders of coastal regions. Using the DPSIR methodology, this literature analysis has permitted to identify, for each WFD biological quality element (except fish), which pressures (or pressure types) are potentially relevant in the light of their impact on the indicators of the ecological status of water bodies. Some metrics and indicators of anthropogenic pressures used in the literature to characterize the sensitivity of the biological quality elements, within quantitative approaches, were also identified. It is also clear from this review that the biological quality elements can be particularly sensitive to intrinsic environmental conditions, and therefore to certain changes related to natural phenomena occurring at large scales (e.g. climate change, paroxysmal climate episode...). Therefore, when one is interested in the sensitivity of biological indicators to different anthropogenic pressures, two factors can complicate the analysis and are likely to weaken the resulting statistical relationships: on the one hand, the variability of biological responses depending on the natural context and, on the other hand, interactions (so called synergistic effects) between different types of anthropogenic pressures and the alterations they can generate.

Caractérisation du fonctionnement d'une hydrolienne à membrane ondulante pour la récupération de l'énergie des courants marins

This manuscript presents three approaches : analytical, experimental and numerical, to study the behaviour of a flexible membrane tidal energy converter. This technology, developed by the EEL Energy company, is based on periodic deformations of a pre-stressed flexible structure. Energy converters, located on each side of the device, are set into motion by the wave-like motion. In the analytical model, the membrane is represented by a linear beam model at one dimension and the flow by a 3 dimensions potential fluid. The fluid forces are evaluated by the elongated body theory. Energy is dissipated all over the length of the membrane. A 20th scale experimental prototype has been designed with micro-dampers to simulate the power take-off. Trials have allowed to validate the undulating membrane energy converter concept. A numerical model has been developed. Each element of the device is represented and the energy dissipation is done by dampers element with a damping law linear to damper velocity. Comparison of the three approaches validates their ability to represent the membrane behaviour without damping. The energy dissipation applied with the analytical model is clearly different from the two other models because of the location (where the energy is dissipated) and damping law. The two others show a similar behaviour and the same order of power take off repartition but value of power take off are underestimated by the numerical model. This three approaches have allowed to put forward key-parameters on which depend the behaviour of the membrane and the parametric study highlights the complementarity and the advantage of developing three approaches in parallel to answer industrial optimization problems. To make the link between trials in flume tank and sea trials, a 1/6th prototype has been built. To do so, the change of scale was studied. The behaviour of both prototypes is compared and differences could be explained by differences of boundary conditions and confinement effects. To evaluated membrane long-term behaviour at sea, a method of ageing accelerated by temperature and fatigue tests have been carried out on prototype materials samples submerged in sea water.