Floods; designation of floodplains

The most effective way to avoid flood damage is to prevent potential damage in areas at risk of flooding from occurring in the first place. The Federal Water Act obliges the federal states to designate as floodplains at least those areas within risk areas or assigned areas in which a flood event is statistically expected to occur once every 100 years and the areas used for flood relief and retention.

In Bavaria, there is a need to identify floodplains on all larger watercourses, the first and second order watercourses with a total length of 9,000 km, and above all in settlement areas on the smaller watercourses, the third order watercourses. These areas are defined by legal ordinance of the district administrative authority.

A digital terrain model, survey data and the evaluation of land use data and aerial images form the technical basis. This allows a flood event to be simulated, which statistically occurs once every 100 years, and the corresponding flood area to be determined.

The water management authorities submit these results in the form of site plans to the district administrative authorities for approval.

Various prohibitions apply in designated floodplains. For example, no new building areas may be designated in urban land-use plans or other statutes in accordance with the German Building Code in designated floodplains. Exceptions are only possible under strict legal conditions.

• Art. 46 Bavarian Water Act (BayWG)

  Floodplains along surface waters

• § Section 76 of the Water Resources Act (Wasserhaushaltsgesetz - WHG)

  Floodplains along surface waters

• Official determination of floodplains (Bavarian State Office for the Environment)

• Floods; information from district administrative authorities