Reconnected Floodplain

Organization: KUEI - Catholic University of Eichstätt-Ingolstadt / FAU - Friedrich-Alexander-Universität Erlangen-Nürnberg (Germany)

Floodplain re-connection by technical re-establishment of hydrologic dynamics and restoring of ecological functions along a stretch of the Upper Danube in Bavaria, Germany (KUEI).

General Info

The pilot site DPS2 is an 8 km stretch of the Danube's left bank between Bergheim and Ingolstadt, within a 2,100 ha floodplain forest in Bavaria. This area, one of Germany's largest floodplain forests, lies between the Alpine foothills and the German low mountain ranges. The Danube's flow, influenced by alpine tributaries Iller and Lech, causes frequent summer floods and low water in late fall and early winter.

High water levels from alpine snowmelt can lead to ecological flooding. The Danube valley, a fluvio-glacial region, includes diverse water features like the Längenmühlbach, Zeller Canal, and the "Old Danube" oxbow, reconnected through a project. Numerous ponds, flood channels, and gravel-mining lakes enhance the area's hydrological diversity.

Effective renaturation relies on understanding soil and aquiclude layers. The pilot area is internationally significant, part of the NATURA 2000 network, and includes various ecosystems such as forests, water bodies, reed beds, and burns, covering 90% of the project area.

What measures have been taken?

The "Dynamization of the Danube floodplains between Neuburg and Ingolstadt" project, led by the Ingolstadt Water Management Office and completed in 2011, was initiated by the Free State of Bavaria to mitigate adverse changes in the Danube. Its primary goal was to restore floodplain conditions through strategic measures.

Ottheinrichbach Watercourse/Detour Structure

• Length: 8 kilometers
• Purpose: Restore continuity, groundwater dynamics, and cross-linking of the Danube with its floodplain.
• Function: Bypass watercourse for fish, reconnecting headwaters and tailwaters of the Bergheim barrage.

Reconstruction of the Bergheim Barrage Overspill Weir

• Purpose: Enable ecological floodings through controlled "flood pulses."
• Function: Channel up to 25 m³/s of Danube water into the Längenmühlbach, mimicking natural floodplain dynamics.

Groundwater Lowering

• Construction: 2.1 km drainage ditch.
• Purpose: Increase groundwater fluctuations and lower unnaturally high groundwater levels.
• Function: Promote the development of alternating water zones in the "Old Danube."

Environmental Impact

Vegetation Impact:

• Shifts in species composition were observed along transects and monitoring plots.
• Influenced by Ottheinrichbach water levels, promoting positive responses in aquatic and riparian vegetation.

Hydromorphological Changes:

• Sediment rearrangement and near-natural course development of Ottheinrichbach.
• Habitat modifications and formation of natural sand and gravel bars.

Water Quality and Groundwater Dynamics:

• Significant fluctuations were observed, beneficial for vegetation and floodplain stages.

Wildlife Corridors and Fauna:

• Improved fish habitats through fish passes and ecological floodings.
• Support for terrestrial fauna, indicating increased biodiversity.

Overall Impact:

• Successful rejuvenation of the ecosystem.
• Achievement of project goals through comprehensive restoration measures.

Recommendations

The "Dynamization of the Danube floodplains" project between Neuburg and Ingolstadt has successfully introduced controlled flood dynamics, benefiting ecosystem health and diversity. While not fully self-sustaining yet, it marks a significant improvement from previous regulated conditions and has partially restored ecosystem functions lost due to dam construction. Complete reversal to the original floodplain forest ecosystem is deemed impractical. Recommendations include optimizing flood dynamics to support native plants, increasing water level variability, and implementing ecological flooding to mimic natural processes. These efforts aim to sustain biodiversity and ensure ongoing restoration of the floodplain ecosystem.