Hybrid Modelling Approach to Study Scour Potential at Chancy-Pougny Dam Stilling Basin

Chancy-Pougny is a run-of-river dam on the Swiss-French border constructed in the early 1920s. Since its inauguration, the operation of the four spillway gates was responsible for a progressive erosion of the stilling basin. Thus, a hybrid modelling was performed to study the scour potential and to determine adequate solutions to maintain future scour within acceptable levels. Visual observations on the physical model identified a strong recirculation in the non-symmetrical basin, that combined with the outflow from the spillway gate, lead to an enhanced specific discharge and to the formation of a turbulent vortex impacting the rocky foundation. Some measures to limit the recirculation, including a free-standing wall and various configurations of concrete prisms for scour protection, were tested on both the physical and numerical model. The pressure and water depth measurements resulting from the physical model were used within the numerical model to determine the corresponding scour potential for each of the tested mitigation measures. A solution containing a layer of randomly distributed concrete prisms laid on the basin’s current bottom was identified through this study, proving the importance of both numerical and physical approaches in hydraulic engineering.

Hybrid modelling approach to study scour potential of Chancy-Pougny dam stilling basin

Erik Bollaert, Sabine Chamoun, Giovanni De Cesare, Anton Schleiss, Davide Wüthrich

2017

Experimental and Numerical Study on Scour-Protection Methods in a Stilling Basin: Case Study of Chancy-Pougny Dam

Erik Bollaert, Sabine Chamoun, Giovanni De Cesare, Anton Schleiss, Davide Wüthrich

Chancy-Pougny is a run-of-river dam on the Swiss–French border constructed in the early 1920s. Since its commissioning, the operation of the four spillway gates has been responsible for a progressive erosion of the stilling basin. The future scour potential of the unlined stilling basin of the Chancy-Pougny dam was assessed by hybrid modeling, combining both a physical and a numerical model. The physical model investigated the flow structure in the basin as well as the dynamic pressure fluctuations exerted by the flow on the rocky bottom of the stilling basin. The presence of a large gyre, generated by a flow recirculation in the nonsymmetrical basin, was found to be one of the main causes of significant scour formation. The numerical model used the pressure recordings to reconstitute the observed scour since 1924, predicting significant additional long-term erosion in the stilling basin. As such, a series of scour mitigation measures, including a free-standing wall and various configurations of concrete prisms for scour protection, were tested on both models. A tailor-made solution containing a layer of randomly distributed concrete prisms laid on the basin’s current bottom was identified through this study, proving the importance of both numerical and physical approaches in hydraulic engineering.

2021

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

Martin Peter Bieri, Michael Müller

2010