Renaturation of the Dahle floodplain

The Challenge

As part of the compensatory measures for the Außig flood polder project, the goal was to relocate the straightened course of the Dahle River back into its original bed. This restoration had to respect existing tree populations and enable natural development within the project area, in alignment with the EU Water Framework Directive. The challenge lay in balancing ecological restoration with technical feasibility, while enhancing the landscape’s resilience to flooding and supporting biodiversity.

The Solution

Tractebel designed a comprehensive ecological restoration plan that reintroduced river loops and added diverse structural elements such as bays, steep banks, gravel and sand banks, groynes, and deadwood to enrich habitat diversity. Riparian vegetation was established, and floodplain shrubs and deciduous trees were planted to support ecological succession. Intensively used grasslands were targeted for transformation into species-rich meadows through extensive maintenance. The old riverbed was partially filled to function as a drainage basin and flood channel during high water events, while adjacent depressions were created as amphibian spawning grounds. A new combined sewer system was also constructed to manage private and public discharges into the former river course.

The Impact

The project has successfully transformed the Dahle River into a vibrant and ecologically valuable watercourse that meets EU environmental standards. The restored landscape now supports a rich mosaic of habitats, improves flood resilience, and enhances the natural character of the area. This initiative demonstrates how compensatory measures can deliver meaningful ecological and hydrological benefits, contributing to sustainable water management and regional biodiversity.