RÉSUMÉ. -Le réchauffement climatique est une réalité alarmante et conduit probablement à une augmentation de la pression sur les systèmes socio-économiques. Cependant, dans les régions de haute-montagne, il pourrait induire l'opportunité d'adapter des aménagements hydroélectriques existants, ou de développer de nouveaux projets. Dans les Alpes, le recul des glaciers produit tout d'abord, principalement l'été, une augmentation du volume annuel de fonte selon les caractéristiques du glacier et du bassin versant dans lequel il se trouve. A partir d'une certaine surface du glacier, la perte de surface ne compense plus la hausse de l'ablation et une diminution significative des apports liés aux glaciers doit être considérée pour l'exploitation hydroélectrique. En outre, la diminution des surfaces englacées libère de nouvelles surfaces, dont certaines ont un potentiel pour la construction de nouveaux barrages. L'opportunité de construire de nouvelles retenues et centrales hydroélectriques juste à l'aval de glaciers en recul est étudiée à l'aide de deux modèles. Le premier (GlabTop) est utilisé pour prévoir la future topographie et géomorphologie sous les glaciers afin de déterminer l'emplacement optimal de nouvelles retenues. Deuxièmement, le modèle hydrologique-hydraulique RS3.0 CLIMATE simule l'évolution du glacier et du débit à l'exutoire des bassins versants ainsi que la production hydroélectrique. Le cas du haut bassin versant de l'Aar en Suisse est présenté. La possibilité d'y construire un nouveau barrage et une nouvelle centrale est étudiée, incluant une évaluation de la rentabilité. Le résultat donne une base pour évaluer l'opportunité d'investir dans de tels projets pour assurer l'approvisionnement hydroélectrique futur en Suisse et de fournir l'éner-gie de pointe pour le réseau européen. Mots-clés : nouveau lac, retrait glaciaire, changement climatique, hydroélectricité Impact of glacier shrinkage and adapted hydropower potential in the Swiss AlpsABSTRACT. -Global warming is an alarming reality and likely leads to an increase of multiple pressures on socio-economic systems. However, in high-mountain regions it might also become an opportunity to adapt existing hydropower schemes and to develop new projects to this reality. In the Alps, the melting of glaciers first produces over the near future an increase of the average annual discharge depending on glacier and catchment characteristics, especially during the summer season. Nevertheless after a certain time, significant decrease of runoff related to glacier melting must be considered for hydropower management. Moreover, the shrinking glaciers free new areas, having the potential for the construction of new dams and reservoirs. The opportunity to build new dams and hydropower plants downstream of retreating glaciers is studied using two models. The first (GlabTop) is used to predict the future topography and geomorphology underneath the melting glaciers, in order to define the optimal locations of the future dams and reservoirs. Secondly, the RS3.0 CLIMATE ...
Sudden starting and stopping of turbines and pumps lead to highly unsteady flow in tailrace channels of hydropower plants (HPP). Submergence of Pelton turbines and air entrainment in pumps due to surge waves must be avoided by technical measures. The existing 240 MW Veytaux pumped-storage plant in Switzerland will be enlarged by a new powerhouse adding another 240 MW, using the same tailrace channel and intake. Therefore, surge waves, induced by the two combined HPPs' operation, were investigated using a physical model. For its validation, the flow behavior of the present scheme was tested and compared to prototype measurements. The enhanced scheme was investigated to analyze critical scenarios, to optimize the plant operation rules, and to define its limits. The effect of the layout on wave reflection in pump mode is highlighted and compared to theoretical approaches.
Stepped spillways are frequently limited to specific discharges under around 30 m2/s due to concerns about potential cavitation damages. A small air concentration can prevent such damages and the design of bottom aerators is well established for smooth chutes. The purpose of this study is to systematically investigate the performance of a deflector aerator at the beginning of stepped chutes. Six parameters (chute angle, step height, approach flow depth, approach flow Froude number, deflector angle and deflector height) are varied in a physical model. The spatial air concentration distribution downstream of the aerator, the cavity sub-pressure, water discharge and air discharges are measured. The results describe the commonly used air entrainment coefficient, the jet length, as well as the average and bottom air concentration development to design an aerator. The lowest bottom air concentration measured in all tests is higher than the air concentration recommended in literature to protect against cavitation damages. And, unlike smooth chutes, there appears to be no significant air detrainment downstream of the jet impact. One deflector aerator seems therefore sufficient to provide protection of a stepped spillway.
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