Does restoration of flooding and reconnection of anastomosing channels in the upper Rhine floodplain improve alluvial ecosystem functions and biodiversity?
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16 juin 2008
- handle: 10670/1.v7h3kd
- halshs: halshs-00661380
Mots-clés
Upper Rhine "Erstein polder" restoration of flooding anastomosing channels reconnection multi-disciplinary monitoring Erstein polderSujets proches
Flooding InundationsCiter ce document
Michèle Trémolières et al., « Does restoration of flooding and reconnection of anastomosing channels in the upper Rhine floodplain improve alluvial ecosystem functions and biodiversity? », HAL-SHS : géographie, ID : 10670/1.v7h3kd
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Résumé
Hydraulic works on large rivers have drastically modified the structure and the functioning of alluvial ecosystems. In particular they have led to disconnection of anastomosing and/or braiding channels, and alluvial forests from the main channel. Nowadays many projects of restauration are developed aiming at both flood retention and ecological restauration. One of the objectives is to restore river functional characteristics of the alluvial ecosystems such as surface water/groundwater exchanges, lateral hydrological connectivity, water purification, diversity of habitats and species. Within the Upper Rhine floodplain (eastern France), the "Erstein polder" is a pilot site which allows the monitoring of the impact of alluvial areas re-flooding. The re-flooding of the polder by flood waters, which are usually highly charged with suspended and soluble matter, may change the physical and chemical compposition of different compartments -water, sediment and soil- of the alluvial system. Additionally, the hydrodynamics of the anastomosing channels is enhanced by the re-flooding and the reconnection with the main channel. The objectives of the monitoring are : i) to identify the risks of water pollution, related to transfer of floodwaters into the groundwater. This requires the monitoring of pollutants brought by the Rhine; ii) to define the impact of floods on habitats, flora and fauna through relevant biological indicators; iii) to analyze the ability of the alluvial system to recover its specific functions. Since 2003 (reference year) two types of studies were conducted, one focusing on the hydrological, hydraulic, hydrochemical and geomorphological factors, the second addressing the impacts of these factors on biological compartments (terrestrial and aquatic plants, fishes, amphibians and invertebrates). Four short flood events occurred during the investigation period (2004-2007). We present the main results of the observed changes as a consequence of re-flooding and channel reconnection obtained after four years of monitoring.