Different types of land use are typical for the Rhine valley. Within the Hördt retention area, for instance, agriculture, forestry,
leisure and recreation as well as nature conservation compete with one another. As the floodplain is sparsely populated and lacks major industrial activities, the planned retention area for extreme flood events is an important habitat for endangered species. Such an unusual flood event is, therefore, expected to cause considerable damage to the local biocoenosis.
The regional plan for the Hördt retention area identifies ecological flooding as an innovative tool for minimising damage to local floodplain habitats and species. The main objective is to give plants and animals a chance to adapt to high water levels during a flood event. Three closures in the main dike will reconnect the formerly isolated floodplain in Hördt with the river Rhine. This will lead to fluctuating water levels and will increase the water supply within the retention area in a sustainable way. As a result, the local biocoenosis will slowly adapt to high water levels and is expected to cope with the challenge of an extreme flood event. Ecological flooding should begin step-by-step in small sub-areas of minor importance for nature conservation. The procedure will start in sub-area 1 and 2, as shown in figure 1. Intensive monitoring will follow, in order to prove the expected development predicted by the experts. Favourable results will allow other parts to be investigated as potential ecological flooding areas.
Flood retention, in combination with ecological flooding, is able to reduce the damage to natural habitats caused by extreme flood events, particularly in former floodplains that have been cut off from the river as a result of human activity. „La Bassée“, the French ALFA-partner’s project in the Seine catchment, was designed to pump water into former floodplains in the event of extreme flood events. The Hördt
example shows that ecological flooding could be an appropriate device for remodelling a biocoenosis and allowing habitats and individuals to adapt to the high water levels in order to minimize the damage on nature caused by a retention event.
Figure 1: tree frog
Figure 2: Classification of the retention area based on topographical and ecological criteria and different types of land use
