Author(s): Andris Wyss; Florian Hinkelammert-Zens; Robert Boes; Michael Muller; Adrian Stucki; Volker Weitbrecht

Linked Author(s): Michael Müller, Volker Weitbrecht, Robert Boes

Keywords: flood protection; flood diversion tunnel; intake structure; physical scale model

Abstract: The flood diversion tunnel from the River Sihl into the Lake of Zurich is going to protect the city of Zurich from extreme floods of the River Sihl by diverting the flood peaks into Lake of Zurich. A key element of the tunnel is the intake structure. It must ensure that in the event of a design flood (500-year flood with peak discharge QP = 600 m3/s), slightly more than half of the dis- charge (QT = 330 m3/s) is diverted into the tunnel. To check and eventually optimize the diversion characteristics and other hy- draulic aspects, the intake structure was investigated in a physical scale model. The model tests confirmed that the planned diver- sion characteristics were achieved. Furthermore, the model tests showed that the hydraulic conditions in the river enable bed load transport downstream past the intake structure without entering the diversion tunnel. However, in the case of small flood events (10-year floods and below), when no water is diverted into the tunnel, bed load transport was found to be impaired due to the original channel geometry that led to backwater conditions and reduced bed shear stresses. By changing the bed topography and anticipating the accumulations of bed load on gravel bars, the continuity of bed load transport could be improved. In addition to these investigations on hydraulics and bed load transport, the intake structure was tested under different scenarios regarding large wood transport and extreme load cases. All tests confirmed the robustness of the intake structure.

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

Year: 2024