Impacts écologiques des éclusées hydroélectriques. Caractérisation des régimes d’éclusées et Retour d’expérience sur la Maronne

Les éclusées hydroélectriques peuvent impacter de manière conséquente les populations de poissons, et plus particulièrement compromettre le recrutement des espèces diadromes comme le saumon. Pour progresser dans la compréhension des impacts et la définition des mesures de mitigation, il s’avère nécessaire de coupler des suivis biologiques long-terme, une analyse hydrologique avec une caractérisation des régimes d’éclusées, ainsi qu’une approche hydromorphologique. Une méthodologie de caractérisation hydrologique des régimes d’éclusées est dans un premier temps présentée. Leur diversité et leur importante variabilité sont illustrées. On présente ensuite le retour d’expérience acquis sur la Maronne, cours d’eau affluent de la Dordogne en aval d’Argentat soumis aux éclusées de l’aménagement de Hautefage. Les suivis biologiques et les études hydrologiques et hydromorphologiques ont permis de mieux appréhender et quantifier certains impacts (exondations de frayères, échouages-piégeages d’alevins), d’étayer des mesures de mitigation et d’en évaluer l’efficacité. L’intérêt de travaux ponctuels sur la morphologie en complément des mesures sur la gestion des débits est également illustré. Des résultats positifs ont déjà été obtenus. Les réflexions se poursuivent sur la Maronne pour obtenir une situation vraiment satisfaisante. Cet exemple montre que l’état actuel des connaissances ne permet pas, sur un cours d’eau donné, de prédéfinir des mesures de mitigation des impacts des éclusées, tout en garantissant leur efficacité. Cela amène à prôner la mise en place de démarche d’étude similaire sur d’autres cours d’eau, pour identifier les réponses des communautés biologiques en fonction des caractéristiques des éclusées et des hydrosystèmes

An experimental study on fish-friendly trashracks – Part 2. Angled trashracks

Experimental results for fish-friendly trashracks placed in an open water channel are presented. Model trashracks with different bar shapes, spacing and angles were tested. The numerous configurations provided results on head losses and on changes in velocity along the rack for a large range of situations, including fish-friendly trashracks. Previous head-loss equations found in the literature were applied to these configurations and were compared with measurements. A new head-loss equation is proposed that takes into account the effect of the different tested parameters. Velocity measurements provided new results and answers concerning downstream-migration aspects such as admissible approach velocities and guidance efficiency as a function of the trashrack angle

Hydraulic Resistance of Emergent Macroroughness at Large Froude Numbers: Design of Nature-Like Fishpasses

The mean flow in a nature-like fishpass can be highly modified by the Froude number. It is important to understand this evolution to correctly design the structure. The studied configuration is an emergent staggered arrangement of obstacles. The hydraulic resistance of a fishpass is experimentally investigated that depends on several geometric parameters: block shape, ramp slope, block density, and bed roughness. An analytical model based on the balance momentum allows one to quantify the influence of each hydraulic parameter. The bed roughness has a weak influence, whereas the block shape and the Froude number are significant. The variation of the drag coefficient was analyzed to improve the stage-discharge relationship. To this end, a correlation with the block diameter and water level is proposed. The maximal velocity reached in the fishpass can also be estimated. These results have to be compared with the fish swimming ability to assess the fishpass passability

Hydrodynamique de prises d'eau munies de plans de grilles orientés

Dans le cadre des directives européennes SER (Développement d'Énergie Renouvelable), DCE (Directive Cadre sur l'Eau), et des plans de restauration de la continuité écologique (Trame bleue, Plan de gestion de l'anguille), la nécessité de limiter, voire d’annuler, les dommages liés à la dévalaison des poissons au niveau des centrales hydroélectriques (mortalités au passage par les turbines) apparaît comme une priorité. Les contraintes biologiques de nombreuses espèces de poissons, essentiellement migratrices, doivent alors être intégrées dans la conception des prises d’eau dites ichtyocompatibles, au même titre que les dimensionnements hydraulique et mécanique. L’objectif est d’obtenir des taux de survie des poissons dévalant proches de 100% au niveau de chaque aménagement, de manière à limiter l’impact cumulé sur les axes de migration [...

Closure to “An experimental study on fish-friendly trashracks: part I & II”

The Authors thank the Discussers for their observations on our two papers. Four main points, related to head-loss predictions for angled trashracks, have been underlined by the Discussers and are discussed here.[...

Numerical simulations of fish-friendly angled trashracks at model and real scale

Several amphihaline species, such as silver eels, suffer high mortality rates during their downstream migration, due to their passage through turbines. The combination of adapted trashracks (inclined or angled screen, lower bar spacing, …) with bypasses can efficiently prevent these mortalities. A numerical study has been carried out with such angled trashracks. Numerical results with model scale racks were validated against previous experimental results on model trashracks, resulting from head loss and velocity distribution measurements (Raynal et al., 2013). Real scale racks were then computed in order to evaluate the influence of both the bar spacing and the channel width on velocity distributions in real dimensions. The mesh generation and the numerical simulations were performed by the open source CFD software suite OpenFOAM. The trashrack solid comprised basic elements, individually created using CAD software and directly inserted in OpenFOAM’s mesh generation utility. For small scale configurations, grid refinement was applied at the flume walls, at trashrack bars and downstream of the trashrack, whereas only bars were refined for real scale racks. The resulting number of cells ranged between 100,000 and 1,500,000. Steady state results were obtained by solving the Reynolds-averaged Navier-Stokes (RANS) equations for an incompressible and monophasic flow. The k-ε, k-ε-based RNG, k-ω, k-ω-based shear stress transport (SST) and Spalart-Allmaras models were examined to select the most appropriate one in terms of computation time and result accuracy. Results show that the k-ε-RNG is the model best agreeing with experimental results. Two-dimensional calculations seem to provide quite satisfactory results although both the head losses and the size of the recirculation zone downstream of the trashrack are slightly under-estimated. Real scale results confirm experimental ones and show that the bar spacing slightly effects upstream velocity profiles. Downstream of the rack, simulations with different flume width demonstrated that the size of the recirculation zone is proportional to the channel width

Study on fish-friendly inclined and angled trashracks

This paper presents the results on trashrack head losses obtained by Raynal et al. [2013 a,b], [2014] for several configurations. More especially, it compares the head loss formulae proposed in these studies with various equations from the literature to improve energy losses prediction in fish-friendly configurations. These new predictive laws of head losses are applied to the renovation of a hydropower plant and show that inclined trashracks or angled trashracks with streamwise bars are reliable solutions when the bar spacing is reduced

An experimental study on fish-friendly trashracks – Part 1. Inclined trashracks

Experimental results are presented for trashracks placed in an open water channel with different bar shapes, spaces between bars and screen inclination angles. The numerous configurations provided results on head losses and on changes in velocity along the rack for a large range of situations, including fish-friendly trashracks. A new head-loss equation is proposed that takes into account the effect of the different tested parameters and demonstrates the need to separate the effect of the trashrack bars, which is directly related to the inclination of the trashrack, from the effect of the transversal elements such as spacer rows whose effect on the flow is not altered by rack inclination. Velocity measurements also adduce rules for efficient water intakes complying with fish-friendly criteria

Scale effects of turbulence in vertical slot fishways : field ans laboratory measurement investigation

Scale effects arise due to force ratios which are not identical between a model and its full-scale prototype and result in deviations between the scaled model and prototype observations. This paper describes scales effects in vertical slot fishway flow by comparisons of turbulence behaviours measured in 1:4 scale laboratory model and full-scale fishway. Full-scale measurements are exposed. Flow topology, mean flow and unsteady velocity components features, turbulence kinetic energy profiles are evaluated and compared to measurements model

L'alchimie poétique d'Alejandro Jodorowsky

Le caractère pluridisciplinaire de l’œuvre d'Alejandro Jodorowsky est l'un des éléments fondamentaux de son parcours d'artiste. Les productions cinématographiques, les bandes dessinées ou encore ses apports sur le tarot sont autant de particularités qui ont fait sa popularité. Sa poésie surgit dans les années 2000 avec la publication de ses premiers recueils, pourtant, Jodorowsky adoptait déjà un comportement poétique dans les années 1960 lors de la création de Panique ou en 1973 lorsqu’il portait à l'écran La Montagne sacrée (La Montaña sagrada). Dans cet article nous montrerons comment la poésie est au cœur de son art et fait le lien entre ses nombreuses productions. La poésie pour Alejandro Jodorowsky est en effet avant tout une pensée et un acte qui, conjointement, permettent la naissance de ses multiples pièces. L'acte poétique apparaît déjà à l'artiste au Chili dans les années 1950, cette philosophie de la poésie se consolidera ensuite dans les années 1960 et 1970 en France.Alejandro Jodorowsky’s multidisciplinary aspect is one of the fundamental elements of his artistic journey. The cinematographic productions, the comics or yet again his contributions on Tarot are as many particularities that make him known to many. The poetry arose in the 2000’s with the publication of his first collections, yet, but it was already present in the 60’s during the creation of “Panic” or in 1973, when Jodorowsky brought The Holy Mountain to the screens. In this article, we will demonstrate how poetry is the heart of his art and the unifying link of his many productions. Poetry, for Alejandro Jodorowsky, is indeed and above all a reflection and an act, that conjointly, allowed the birth of his numerous plays. The poetic act already appears to the artist in Chile during the 50’s, this philosophy of poetry will then consolidate itself during the 60’s and 70’s in France