The Restoration of Former Channels in the Rhine Alluvial Forest: The Example of the Offendorf Nature Reserve (Alsace, France)

The hydraulic management works, carried out on the Rhine over about 150 years, have suppressed a large part of the Rhine floodplains and thus dramatically modified the environmental conditions of alluvial ecosystems. The Offendorf alluvial forest situated 30 km north of Strasbourg, of which 60 ha are now a nature reserve, is taken as an example of a restoration programme to attain “the most natural possible” ecosystem functioning. The general status of the Offendorf forest hydrographic network is mesotrophic to eutrophic, due to the water supply. Some diffluent arms present a tendency to silt up, because of the lowering of the water table. Thus a first step in the restoration programme was to re-establish the continuity of surface flow, in low as well as in high water, taking into account the water quality. But the accurate context of the restoration is that of a naturally functional unit, i.e. the whole extent of the forest lying between the high water dykes and not the limited sector within the administrative boundaries of the nature reserve.

A definition of a restoration programme is proposed: the renaturalizing of the riverside environments should comprise several stages from study of the past or present processes to prediction of new modifications.