Mitigating scour in aging run-of-river hydropower infrastructure: an analysis of pressure fluctuations in the physical model of Chancy-Pougny (Switzerland)

Many run-of-river hydropower plants built without stilling basins now experience progressive scour due to prolonged operation and increasingly frequent floods. The Chancy-Pougny dam on the Rhône River, constructed in the 1920s at the Swiss-French border, exemplifies this issue. Severe flow recirculation was identified as the main cause of erosion, with pressure fluctuations increasing between the original and current stilling basin. While earlier work developed scour protection measures through physical modelling and numerical predictions, the present study focuses on analyzing pressure measurements within the stilling basin to assess how fluctuations can be reduced to limit future scour. Effective mitigation strategies include: (1) raising the basin water level, (2) introducing a guidance wall to restore symmetrical flow, and (3) adding various configurations of half-cube concrete prisms to increase roughness and energy dissipation. A Life Cycle Assessment of prism materials and construction methods further supports a sustainable approach to rehabilitating ageing hydraulic infrastructure.