Flood retention and forestry Water friendly land management in the retention area for extreme flood events in the Hördt floodplain Background, goal and scope The German state of Rhineland-Palatinate recently started the implementation of one of its biggest retention areas along the River Rhine. It is about 870 ha and will have capacity to store up to 32 million cubic meters of flood water. Designed for extreme flood events the retention area will feature a unique water inlet with the dyke serving as a weir at special points allowing water to flow over only when the level of the Rhine exceeds a 1:200 years flood event. The land in the retention area is used and managed in various ways (see table below). One third of the prospective retention area is used for agriculture two thirds are covered with trees for sustainable forestry thus providing jobs and income for the local population. Multifunctional land use in the Hördt floodplain Established Future Forestry, sustainable and commercial   Agriculture, commercial   Nature conservation (SPA, SAC, nature reserve)   Recreation (hiking, cycling)   Fishing   Hunting   Hördt Cultural heritage (pilgrim’s route to Santiago)   Ecological floods  Retention area in extrem flood events  Results and conclusions

Tree species Flood water field level willow poplar oak pine birch plane oak/pw pine walnut maple Flood sensitive species out

• Common beech (Fagus sylvatica) • Norway maple Fluttering elm (Acer pseudoplatanus) (Ulmus laevis) Tree species Flood water • Sycamore maple horn- black sycamore norway cherry level lime locust buckeye ash beech beam elder maple maple (Acer platanoides) • Common ash (Fraxinus excelsior)

Flood tolerant Ref.: RP Freiburg (2007): Risikoanalyse Wald. – Materialien zum Integrierten Rheinprogramm, Bd. 12, modified species in Field maple As well as forest conversion towards flood tolerant tree species and a change in (Acer campestre) forest management practices ecological floods (regularly low level floods • Common oak corresponding to the water dynamics of the River Rhine) will be implemented up (Quercus robur) to a predefined level. This is a training concept for the environment in order to • Fluttering elm minimise potential impacts in case of an extreme flood event. (Ulmus laevis) In order to minimise huge flood damages on the forest ecosystem and to • Field maple guarantee sustainable forestry, flood sensitive species are taken out and (Acer campestre) substituted by more flood tolerant species. Common Oak, Fluttering Elm, Field Maple and Yew are able to withstand floods for up to three months. These • Yew tree (Taxus baccata) YewYew Tree tree species can help to guarantee sustainable forestry within a retention area (Taxus(Taxus baccata baccata) ) during extreme flood events.

Heinz Peter Wierig, SGD Süd – Struktur- und Genehmigungsdirektion Süd, Speyer, Germany, www.sgdsued.rlp.de,

e-mail: [email protected] Field Maple (Acer campestre) Walter Kretschmer, IUS – Institut für Umweltstudien Weibel & Ness GmbH, Heidelberg, Germany, www.weibel-ness.de, e-mail: [email protected]

Acknowledgement: This work was co-funded by the European Commission through the INTERREG IVB North West Europe project ALFA (Adaptive Land use for Flood Allevation, project number: 018A ALFA)