Foundations of flood forecasting in meso-scale catchment areas of Switzerland

A comprehensive flood assessment model based on long-term simulations is now available for the Rhine River catchment area. The results of the model for 450 catchment areas can be consulted on the Web site of the University of Bern.

The simple estimation process that is most commonly used provides no other information than peak flow and does not take into account important flood parameters such as flow volume and rise time. To achieve more comprehensive design foundations, stronger process-oriented approaches are necessary. These types of approaches provide information about floods and much more.

The comprehensive flood assessment for unmeasured catchment areas is based on a continuous long-term simulation approach. In this approach, a hydrological model system is used to carry out a continuous simulation over a long period of time - in this case over at least 20 years and at an hourly resolution. The simulated long-term flow data series can then be interpreted with conventional extreme value statistics, among other things, and used to forecast floods.

The results of the modelling process are now available for 450 meso-scale and mostly unmeasured catchment areas in the Swiss Rhine River catchment area.

Not suitable for all applications

Regions with an area of less than 40 km2 show a clear tendency toward underestimating the HQ100. Evaluating the results for an area of less than 25 km2 is definitely not advised. In addition to the size of the catchment areas, karst landscapes also limit its use.

Combining several methods provides additional information

By combining established and new processes and performing a comparatively evaluation of the results, significantly more information can be obtained to estimate rare flood discharges in unmeasured regions.

Experience with the "HQx_meso_CH" programme has shown that the comparative use of different processes provides valuable evidence for estimation and generally leads to more reliable findings than using individual processes alone.

Documenting and obtaining the model results

The method was developed at the Institute of Geography of the University of Bern on behalf of the Federal Office for the Environment (FOEN) and was described at length in two publications.

The report, data and results are available on the Web site of the University of Bern:

Last modification 15.06.2021

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