THE RESTORATION OF FORMER CHANNELS IN THE RHINE ALLUVIAL FOREST - THEEXAMPLE OF THE OFFENDORF-NATURE-RESERVE, (ALSACE, FRANCE)

The hydraulic management works, carried out on the Rhine over about 15 0 years, have suppressed a large part of the Rhine floodplains and thu s dramatically modified the environmental conditions of alluvial ecosy stems. The Offendorf alluvial forest situated 30 km north of Strasbour g, of which 60 ha are now a nature reserve, is taken as an example of a restoration programme to attain ''the most natural possible'' ecosys tem functioning. The general status of the Offendorf forest hydrograph ic 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 co ntext of the restoration is that of a naturally functional unit i.e. t he whole extent of the forest lying between the high water dykes and n ot the limited sector within the administrative boundaries of the natu re reserve. A definition of a restoration programme is proposed: the r enaturalizing of the riverside environments should comprise several st ages from study of the past or present processes to prediction of new modifications.