Flood statistics

Data on flood events is managed and statistically evaluated by the FOEN; the findings are made available in the form of result sheets.

A systematic statistical evaluation of flood data from the discharge measurement network has been carried out since 1986. For a long time the Hydrology Division applied the "Recommendations on flood risk estimation" issued by the German Association for Water, Wastewater and Waste (DVWK 1979; now DWA). From 2014 it has used a new method set, which is explained in the following article:

1. Publication of the results

The results are published in two stages:

  1. A result sheet is published for all the current discharge measurement stations; this can be used for initial approximate flood probability estimates.
  2. For selected stations, detailed station reports can be downloaded. These are mainly intended for organisations specialising in hydrology, for use as a basis for more detailed studies.

2. Contents of result sheets

The maximum annual discharges (checked for plausibility) are used to produce the result sheets. The return levels (discharges for specific return periods) are calculated using the generalized extreme value distribution (GEV).

The front of the result sheet shows on the one hand the annual peak discharge measurement series as a bar chart and on the other the flood probabilities with the estimated distribution function and the measured data as a return level plot. Two tables also list the estimated return levels for the return periods T = 2, 10, 30, 100 and 300 and the five highest annual maximum discharges with their estimated return periods. The back of the sheet contains a range of further information.

The result sheets are used for initial rough estimates of the flood probabilities. Further considerations (e.g. on flooding) are not possible within the framework of these routine assessments. With regard to a specific design situation, more comprehensive studies are required.

3. Contents of the station reports

The station reports are used to detect any non-stationarity in the data, to gain an overview of the discharge quantities calculated using two different approaches for predetermined return periods and to be able to evaluate the difference between them.

In addition to the purely statistical analysis of the flood data, the station reports also contain approximate evaluations of the station's historical metadata and any influences in the catchment area. These should make it possible to optimally embed the statistical results in a specific context.

The results of these statistical analyses only form the basis for answering specific questions, e.g. in determining design discharge. Knowledge of the hydrological processes in the catchment area, considerations of worst-case scenarios for precipitation and runoff etc. are essential for assessment of the flood risk.

4. Further information

Last modification 23.11.2017

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