Hydrometeorological analysis of the 9-10 October 2011 flood event

In the village of Wiler (Lötschental valley, canton of Valais) the Milibach overflowed the channel banks and caused severe damage along its alluvial fan on 10 October 2011 (Jules Seiler, Geoplan AG)

The flood event that occurred on the 10 October 2011 caused severe damage in the cantons of Valais (e.g. Lötschental) and Berne (e.g. Kandertal) as well as in some parts of Central Switzerland. The meteorological situation leading to the flood is quite well understood. Also, surveys and studies carried out in the affected areas immediately after the event reveal that the resulting discharges in the mountain streams as well as the involved damage processes are known. In contrast, the initial conditions of soil moisture and the resulting influence on the runoff processes are not yet fully understood. The same applies to the effect of the snow pack on the flood runoff generation in the damaged catchment areas. Therefore, a multi-level, supra-regional event analysis was initiated to find answers to the questions raised. The strategy of the Federal Office for the Environment FOEN in the prevention against natural hazards ascribes a large importance to the event analysis as a study instrument to assess the causes and consequences of exceptional natural hazard events. Thus, the analyses of past events represent the foundation of the integrated risk management.

The present event analysis was commissioned by the Swiss Confederation represented by the FOEN and emphasizes on the assessment of the meteorological and hydrological forecasts and warnings issued before the event. Also, the potential for optimization of flood early warning activity will be addressed. The supra-regional project is carried out by different specialist departments in the framework of four modules:

• Meteorological analysis by MeteoSwiss

• Snow hydrological analysis by the WSL Institute for Snow and Avalanche Research SLF and geo7

• Hydrological analysis by the Swiss Research Institute WSL and geo7

• Analysis of the operational runoff forecasting activity by the Hydrology division of FOEN

The main goal of the study is a better understanding of the flood event which was significantly influenced by the presence of snow and an improvement in hydrological forecasting of such events in an Alpine environment. The investigations were mainly carried out in the second half of 2012 and the final project report is expected in March 2013. 

Project team

• Alexandre Badoux

• Tobias Jonas

• Massimiliano Zappa

• Markus Hofer

Contact

• Alexandre Badoux