What are floodplains and leaves

Establishment of flood plains


The district government of Cologne defines floodplain areas. In floodplains, actions that could negatively affect flood discharge are prohibited.

The district government of Cologne defines flood plains on the basis of the Water Resources Act (WHG) and the State Water Act NRW (LWG). With the determination, information is provided about which areas will be flooded in the event of a flood, so that those affected can take precautionary and protective measures against flood damage if necessary. In addition, the setting prohibits actions that can have a negative impact on flood discharge.

The definition of a floodplain is based on the area that is flooded by a flood that statistically occurs only once in a hundred years. Since the flooding of an area by a flood event is a natural process, the district government has no discretion in the spatial delimitation.

After a formal procedure, flood plains are determined by an ordinance issued by the authorities. The initiation of a procedure will be announced in the affected communities and cities as is customary. The maps showing the spatial delimitation of the floodplain and the draft of the regulatory authority ordinance are publicly displayed. All those affected then have the opportunity to present their concerns. In this way, any incorrect calculations can be corrected at an early stage.

The regulatory authority ordinances are published in the official gazette for the administrative district of Cologne. In the event of new findings, a stipulation can also be adjusted accordingly beforehand.

A floodplain can be temporarily secured until the assessment process has been completed. No public participation is required for this, only the publication of the maps showing the spatial delimitation and the arrangement in the official gazette of the district government. With a provisional safeguard, actions are also prohibited that could have a negative impact on flood discharge.

Information on the location of floodplains and the contents of the ordinances or provisional safeguards is contained in the overview and the information offered by the Ministry for Climate Protection, Environment, Agriculture, Nature and Consumer Protection of the State of North Rhine-Westphalia (MKULNV NRW).

Correctly read assessment cards

Assessment maps serve to represent the floodplains of individual bodies of water officially established by the authorities. Flood areas are those areas that are flooded during a flood event of at least 100 years, the HQ100.

In general, the assessment maps have a uniform structure: In addition to a large, detailed map section, there is a small overview plan in the upper right corner, with the help of which the viewer can orientate himself. Each body of water is covered by a certain number of leaf sections. These sheet sections form the basis for the large, detailed map section, which each presents a section of the water on a scale of 1: 5000. The overview plan, on the other hand, shows all sheet sections, but emphasizes the sheet section of the respective detailed map. The number of sheet sections and thus also the number of maps on a scale of 1: 5000 depends on the length of the water.

On each map there is a label in the lower right area, on which you can read which body of water it is, which of the map sheets is shown here and what state they are up to date. The contents shown in the assessment cards are listed and explained below:

The officially established floodplain was determined on the basis of the floodplain determined for the HQ100 scenario and is shown in blue. This blue area defines the areas affected by the flood, which are subject to the rules and laws applicable to established flood areas according to the Water and State Water Resources Act.

Official stationing according to GSK edition 3c

The official stationing makes it possible to determine and communicate a location on the water with an exact number of kilometers. The stationing is given in kilometers plus the number of meters. The zero point of the kilometrage is at the confluence with the next larger body of water. The stationing then increases towards the source of the body of water. A point which is, for example, 2.5 kilometers from the mouth is labeled accordingly with km 2 + 500.


Ministry for Climate Protection, Environment, Agriculture, Nature and Consumer Protection of the State of North Rhine-Westphalia (MKULNV NRW): environmental data on siteexternal website Ministry for Climate Protection, Environment, Agriculture, Nature and Consumer Protection of the State of North Rhine-Westphalia (MKULNV NRW): ELWAS - Specialized Information System of the Water Management Administration in North Rhine-Westphaliaexternal website Ministry for Climate Protection, Environment, Agriculture, Nature and Consumer Protection of the State of North Rhine-Westphalia (MKULNV NRW): Flood hazard maps and flood risk mapsexternal website online map service "flood plains" of the Cologne district government (Web-GIS)external website