Crash tests for forward-looking flood control in the city of Zürich (Switzerland)

Abstract

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 km 2 , including also an hydropower reservoir) with peaks exceeding 350 m 3 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.

KULTURisk regional risk assessment methodology for water-related natural hazards – Part 2: Application to the Zurich case study

“…1). If established, these prevention measures could significantly reduce the flood risk of the Sihl to a lower level but details on the expected impact under different prevention measures are still under analysis and discussion (Zappa et al, 2015). Due to this, alternative scenarios have not been considered in this study.…”

“…However, out of the planned ones, only the early warning system (EWS) to forecast extreme events and (Zappa et al, 2015). The complexity of hydrological pattern of the Sihl River valley and the need for a planned strategy of prevention measures demands a broader integrated approach, in order to assess the flood risk to multiple receptors, and a suite of effective tools to identify and prioritize areas and targets at risk in order to finally evaluate the benefits of different prevention scenarios (e.g.…”

Post-Processing of Stream Flows in Switzerland with an Emphasis on Low Flows and Floods

“…At the Swiss Federal Institute WSL, there are two forecast systems running operationally targeting two divergent objectives, one for providing information about droughts in general and low-flow conditions at selected catchments in Switzerland (Zappa et al [6]) and one for forecasting flood events in order to protect the city of Zurich (Addor et al [5] and Zappa et al [66]). In Figure 3, the catchment of the Sihl, which represents the flood forecast system of Zurich, as well as the catchment of the Thur, which is taken as an example of the low-flow forecast system, are highlighted.…”

The KULTURisk Regional Risk Assessment methodology for water-related natural hazards – Part 2: Application to the Zurich case study

“…Earth Syst. Sci., 19, 1561-1576, 2015 mitigate their impact has been implemented so far, while intermediate and long-term prevention measures, such as the overflow channel, are still under analysis and discussion by the different stakeholders and local institutions/authorities (Zappa et al, 2015). The complexity of hydrological pattern of the Sihl River valley and the need for a planned strategy of prevention measures demands a broader integrated approach, in order to assess the flood risk to multiple receptors, and a suite of effective tools to identify and prioritize areas and targets at risk in order to finally evaluate the benefits of different prevention scenarios (e.g.…”

“…Earth Syst. Sci., 19, 1561-1576, 2015 www.hydrol-earth-syst-sci.net/19/1561/2015/ lower level but details on the expected impact under different prevention measures are still under analysis and discussion (Zappa et al, 2015). Due to this, alternative scenarios have not been considered in this study.…”