Lavey Dam - Physical and numerical analysis of flow and sediment transport in the Rhone River

As several of other run-of:river hydropower plants, the hydraulic scheme of Lavey on the Rhone River in Switzerland is concerned by continuous reservoir sedimentation. To determine the flood evacuation capacity of the weir as well as the flow distribution between the four entries of the water intake with and without bed load, a 1 :40 physical scale mode was used. Water levels, flow pattern, flow distribution, sediment deposition and flushing are measured continuously by non-intrusive equipment. Hydraulic tests show that the central dam gate is the most loaded and reveal the importance of three-dimensional phenomena in the curved river reach. The discharge is distributed homogeneously between the four openings of the intake. The test series with bed load allow reproducing the processes of sediment transport in the Rhone River as well as the deposits measured in situ before a flushing event. The prototype behaviour validates the results of physical modelling, including flushing operation. The applied three-dimensional numerical model (FLOW3D (R)) is a powerful complementary tool for generating approach flow pattern and for pre-evaluation and comparison of design alternatives.

Complémentarité de la modélisation physique et numérique à l’exemple d’un aménagement hydroélectrique / Complementarity of physical and numerical modeling using the example of a run-of-river hydropower plant

Martin Peter Bieri, Michael Müller

Comme beaucoup d’aménagements hydroélectriques au fil de l’eau, celui de Lavey sur le Rhône en Suisse est affecté de manière récurrente par l’alluvionnement de sa retenue. Outre la gestion sédimentaire, les thèmes abordés par la modélisation concernent également la capacité de transit des crues au droit du barrage, les écoulements d’approche de la prise d'eau et l’optimisation des consignes d’exploitation de l’aménagement. Les niveaux d’eau, les vitesses et directions d’écoulement, la répartition du débit dans les pertuis, les processus d’alluvionnement et de purge sont ainsi analysés selon une approche stratégique qui s’appuie sur la complémentarité des modélisations numériques et physique. L’approche numérique à degré de complexité croissant est particulièrement intéressante pour la documentation des écoulements à large échelle et pour l’étude préalable des variantes d’aménagement. La simulation du transport sédimentaire confirme cependant l’avantage de la modélisation physique. Cette étude de cas conclut à la complémentarité des modélisations numériques et physique, en soulignant l’importance du calage sur les observations et mesures in situ. Une approche stratégique est finalement proposée pour le choix du ou des modèle(s) adéquat(s), basée sur des critères d’échelle et de problème à examiner.----------------------As several of other run-of-river hydropower plants, the hydraulic scheme of Lavey on the Rhone River in Switzerland is concerned by continuous reservoir sedimentation. The domain of interest of the modeling is the appropriate sediment management, the flood evacuation capacity of the weir, the approach flow of the water intake as well as the exploitation rules of the plant. Water levels, flow velocities and directions, flow distribution between the entries of the water intake, sediment deposition and flushing were analysed by a strategic approach based on the complementarity of numerical and physical modeling. The numerical simulation with increasing complexity level is particularly interesting for large scale flow analysis as well as pre-evaluation of alternatives. The simulation of sediment transport phenomenon confirms the utility of the physical model. This case study confirms the pertinence of the hybrid modeling approach based on a calibration using in situ observations and measures. A strategic approach is finally given for choosing the adequate model(s), based on criteria of scale and phenomenon.

2010

Small Flex : Modèle d’exploitation flexible d’aménagements hydroélectriques de haute chute au fil de l’eau en Valais

Baku Mbenza

The Kraftwerk Rhone Oberwald hydropower was selected as a pilot site to analyze the possibility of running hydropower plants along a river in alpine regions during winter months. The KRO Gletsch-Oberwald hydropower facility has been operating since the beginning of 2018 is a run-of-the-river installation that has been designed without restraint and only works when the Rhone's water supply is abundant, between the May and September. The flow of the Rhone outside this range cannot be turbined and are therefore lost. The project studies the possibility of storing those debris and turbining them in order to provide peak energy despite the lack of upstream basin. These waters will be stored in the settling basin, which is used as a settling basin when flows are plentiful and will pass through holes installed between the Settling basin and the forebay. Secondly, the project studies the sediment dynamics upstream of the intake in order to establish a threshold for the use of the Settling basin as a storage unit and to define the periods during which the settling basin will be used as a sand drap. The project also lists the improvements that should be made at the instrumentation level to reduce uncertainties about the estimates made. This project is part of the activities carried out at the Laboratory of Hydraulic Constructions at the Swiss Federal Institute of Technology in Lausanne as part of the energy transition in Switzerland (Swiss Competence Center for Energy Research - Supply of Electricity) including, in parallel, environmental monitoring activities and studies on the hydraulic machines of the plant.

2020

Martin Peter Bieri, Michael Müller

2010