Hördter Auwald Sustainable forestry and reserve retention capacity for extreme flood water on the Rhine

Hördter Auwald Sustainable forestry and reserve retention capacity for extreme flood water on the Rhine

Under the terms of international treaties, Rhineland-Palatinate is obliged to contribute to the restoration of security against flooding events on the Rhine, which have a probability of occurring once every 200 years. In 1982, France and the German federal states of RhinelandPalatinate, Baden-Württemberg and Hesse agreed to join forces and create retention capacity for a volume of approx. 288 million m³ of flood water. However, floods on the Elbe and Danube in recent years have shown that flood water discharges with a statis ti cal probability of occurring less than once every 200 years can also hit those living and working beside rivers. As a result, Rhineland-Palatinate is providing additional retention areas including the reserve retention area for extreme flood water at Hördt. The development of this area is being subsidised by the EU within the framework of the Interreg Project IVb, ALFA (Adaptive Land use for Flood Allevation). By around 2024, site should Summer flooding in the floodplain forest provide approx. 32 million m³ of water retention capacity over an area of approx. 870 ha to improve protection against extreme flooding events. To this end, as part of the dyke restoration programme, the height of the existing main Rhine dyke (MRD) will be increased along a stretch of approx. 6 km and a new 9.5 km dyke will be constructed along the rear of the flood area. The state of Rhineland-Palatinate will thus make a further important contribution to improving flood protection on the Rhine above and beyond the measures agreed in the treaty.

Currently, the area is protected against flooding by the main Rhine dyke. In future, however, water will be able to flow into the Rhine floodplain at the Hördt site in the case of an extreme flood. Due to the exceptional rarity of flooding on this scale, the natural environment in the area is unable to adapt to flooding of this nature and experts fear that such events could cause major damage. In order to prevent this, there are plans to permit smaller scale ecological flooding. These will prepare the forest and its habitats for the effects of flooding. The future flood water retention area currently has a number of different uses including forestry, agriculture and fisheries, nature conservation and leisure. As ecological flooding could negatively impact on these uses, an intensive consultation process was initiated to determine the best possible balance between the various interests. By permitting flooding at different times and in different areas, it will be possible to ensure that there is no deterioration in the groundwater level in Summer flooding in the floodplain forest surrounding municipalities, the population does not suffer from an increase in the number of mosquitoes, the largest possible retention capacity is available in the reserve area and biological diversity as well as the protection and conservation aims of the NATURA 2000 network are not impaired. In future, during ecological flooding, water from the Rhine will be allowed to discharge into the reserve area through three inlets. This will promote the growth of typical floodplain species and allow the habitats to adapt gradually to future environmental conditions. Wild garlic flowers in the floodplain forest Pollarded willows

Idyll on the Old Rhine

Cultivated poplars Poplar trunks Levels of the floodplain forest Sustainable forestry Around two-thirds of the future retention area is covered by managed forest used for forestry. As the groundwater level in the area has fluctuated little since dykes were constructed along the river more than 100 years ago, it was not necessary to ensure that the trees growing here were tolerant to flood water in the past. This has boosted the natural regeneration of the European beech, for example, but this species is not tolerant to high water levels. Ecological flooding will periodically raise the groundwater level in low-lying parts of the reserve area by up to 1.5 m. In order to maintain good conditions for sustainable forestry under the future scheme, it will be necessary to adapt both the forestry management concept of the reserve area and the Willow composition of its tree species. Low-lying areas where the water level will be higher in future, and which may be subject to flooding several times each year, will be taken out of use as they will no longer be profitable for forestry purposes. Water Nonforested floodplain (Low) softwood floodplain forest Sycamore Maple Ash Oak White elm Poplar Mixture of soft-/hardwood floodplain forest Low, Medium, High, Highest Hardwood floodplain forest

Although it is more flood tolerant than the beech, the rapid spread of ash dieback in Germany since 2007 has led to serious losses of this species and, in the worst case, may lead to its disappearance altogether. The growth of native common oak will be promoted, in particular, to secure the long-term future of sustainable forestry in the planned reserve flood water retention area. When mature, the common oak is able to cope with flood events even in the critical vegetation period very well. It is only sensitive while young and requires approx. five flood-free years at the beginning of its life before it becomes increasingly flood resistant. The white elm, which can live for up to 400 years, is another suitable tree for this environment. It can survive floods lasting three months or more and its wood is particularly hard and resistant to compression Newly planted area An area of approx. 100 ha will be left, for the most part, to develop under its own dynamic. The result will be a range of natural and biologically diverse communities, in which humans will, at most, play a regulating role. In a further area of approx. 70 ha, the focus will be on changing the predominant tree species. Currently, these areas are dominated by species which have little resistance to flooding but are valuable for forestry, such as sycamore maple, Norway maple and European beech. These will be successively harvested and replaced by flood resistant varieties. The common ash will also be removed as part of this programme. Elms and impact. White elms are able to develop buttress roots, which provide them with additional stability in wet ground. They also play an important role in protecting biodiversity as they provide an important habitat for a number of rare types of insect. Moreover, the tree is mostly resistant to a fungal infection transmitted by the elm bark beetle, which causes Dutch elm disease and has been responsible for the drastic reduction in the numbers of our native wych and field elms. A further species with well-developed flood tolerance is the European Yew. While young plants only flourish in the shade of other trees, maturing yews also grow well in full sunlight. Oak, recent floodplain

The Rhine floodplain at Hördt is of major ecological significance. The forested sections are part of the paneuropean conservation area NATURA 2000 due to the presence of many species that are important from a conservation perspective. These include animals that enjoy protection throughout Europe, such as the European tree frog, little grebe, wildcat and weather loach. Protected species on the red list, such as the stag beetle, narrow-mouthed whorl snail and southern damselfly, can also be found here. These important species prefer to settle on floodplains and their populations will benefit significantly from the ecological flooding scheme. The retention area for extreme flood water in Hördt is a model example of multifunctional land use. Traditional economic activities such as agriculture and forestry will be adapted with the agreement of all stakeholders so they can continue alongside and be supplemented by the new role in flood water retention. The ecological flooding programme will restore conditions similar to those found on natural floodplains and thus increase the value of the Hördt floodplain to nature conservation. An educational trail is also planned in order to inform visitors about the interesting local species and conditions in the area. Importantly, the trail will show how to combine sustainable forestry operations with the future use of the area. By changing the make-up of the forest and managing it appropriately, it is possible to provide areas as reserve capacity for extreme flood events and to preserve their role in conservation of the natural environment. White willow Tree frog Wildcat

Kaiser-Friedrich-Straße 1 55116 Mainz Germany Poststelle@mulewf.rlp.de www.mulewf.rlp.de Legal notice: Produced by: Images: Hördter Auwald Sustainable forestry and reserve retention capacity for extreme flood water on the Rhine Struktur- und Genehmigungsdirektion Süd 67433 Neustadt an der Weinstraße www.sgdsued.rlp.de State Forestry Authority of Rhineland-Palatinate Ernst-Christian Driedger IUS Weibel & Ness GmbH ÖKO-LOG Freilandforschung Date: June 2014