Author(s): David Dorthe; Michael Pfister; Stuart Lane

Linked Author(s): Stuart N. Lane, Michael Pfister

Keywords: Dam; flood; modelling; river; temperature

Abstract: Floods are of critical importance for the safety of a dam and its hydraulic structures. Besides, floods play a central role for the ecosystem downstream of a dam. If the powerhouse is located run-off-the-river, then a residual flow reach occurs. The latter is eighter subjected to rather small residual discharges or pronounced floods, both representing extremes of a natural discharge regime. The binary regime of floods versus residual flow as typically occurring downstream of dams’ influences, among others, the streambed exchanges, stream temperature, food availability for the aquatic species, bedload transport and channel morphology of the subsequent river. Floods have been increasingly used during the past as a mitigation measure on such regulated rivers. Monitoring river parameters during artificial floods helps understand their influence and utility. In such a context, river temperatures were measured within the residual flow reach of the Sarine River downstream of Rossens dam (Switzerland) during two floods in October 2020 and May 2022. The evolution of the latter provides insight into the thermal processes occurring during and after a flood, which might be compared to the residual flow regime. Beyond the temperature measurements, the latter were also modelled with a thermo- and hydrodynamic 1D process-based stream model. A reasonable agreement between model and measurement resulted. Results indicate that such models can capture the thermal processes guiding stream temperature at a reach- scale during flood events and hence be a basis of effective artificial flood design.

DOI: https://doi.org/10.3929/ethz-b-000675921

Year: 2024