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.

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A comprehensive understanding of physical phenomena based on a hybrid experimental-numerical approach supports a safer design of critical infrastructures. However, for large-scale tsunami-like waves, the reliability of numerical models was insufficiently validated. Herein, we validate our numerical model of tsunami-like waves by comparing simulation data (obtained using a smoothed panicle hydrodynamics method based on a highly efficient parallel computing technique) with large-scale experimental data for both, dry bed surges and wet bed bores. The presented preliminary results are believed to aid the development of experimentally validated numerical tools for a better understanding of tsunami-like flows.

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Unsteady flows such as tsunamis, impulse waves and dam-break waves can lead to damages and human losses. Hence, specific research to limit casualties and reconstruction costs is needed. The complexity of the phenomena involved suggests that a hybrid experimental-numerical approach should be used to gain a more comprehensive understanding of the process. This paper presents an explorative study on the comparison of SPH numerical simulations using a highly effective parallel computing technique with large scale experimental data for dry bed surges and wet bed bores impacting free-standing buildings with and without openings. These preliminary results showed a relatively good agreement between the two approaches in the estimation of water depths around the buildings, which represents a key parameter for the design of vertical shelters. Nevertheless, some differences observed during the impact phase may be attributed to the incapability of the SPH numerical simulations to fully capture the turbulent nature of the process and its air-entrainment. These validation tests with detailed experimental data are a promising approach to improve the numerical models toward the development of reliable numerical tools for a safer design of resilient structures.@en

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 nonsymmetrical 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 on 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.

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Uncontrolled scour is affecting multiple mobile dams. The plunge pool of the Chancy-Pougny barrage, located on the Rhone River bordering France and Switzerland, has recently been reported to develop in a potentially unfavourable direction after almost 100 years of acceptable scour development. In order to estimate the future scour potential of this asymmetrical plunge pool and validate and optimize possible solutions to limit its development, a physical model was built at LCH-EPFL. First-stage diagnosis tests showed the presence of recirculation surface currents interacting with the spillway outflow jets producing downward vorticity responsible for scour progression. In partnership with the responsible engineering company, different solutions were proposed and tested, starting with the installation of a vertical guide-wall to prevent the formation of the return currents. A solution with randomly-arranged concrete prisms was finally retained as the most favourable compromise between the effective protection of the riverbed and site implementation. Herein the robustness of this solution is analysed for two different, but plausible, operation scenarios. Both the closure of a spillway gate and the lowering of the water level proved the effectiveness of the chosen solution without endangering the stability of the prism-arrangement. The technical solution presented herein enlarges the range of alternative solutions for uncontrolled scour control not only at the Chancy-Pougny barrage but also for a large number of structures with similar layout.@en