Crash tests for forward-looking flood control in the city of Zürich (Switzerland)
Abstract. Floods in the city of Zürich (Switzerland) were already reported in the 13th century. The most severe threat are floods from the Sihl river (336 km2, including also an hydropower reservoir) with peaks exceeding 350 m3 s−1. An assessment using a rainfall-runoff model has been completed to evaluate extreme flood situations by combining 18 precipitation scenarios with different initial conditions. These scenarios identified deficits for the safety of Zürich. For the improvement of flood management several measures are possible. Crash-tests with 41 472 combinations of measures and scenarios have been evaluated. According to the results, the spillway channel option in the downstream reach of the Sihl is a promising structural measure to ensure flood relief for Zürich. Lowering the artificial reservoir lake before the event consistently increases safety also in the upstream part, but causes financial losses in terms of hydroelectricity. The combination of measures can lead to an optimal safety also in case of unfavourable initial conditions. Pending questions concern the costs, political decisions and the environmental sustainability.
