Are socio-economical and eco-morphological objectives compatible in floodplain lake rehabilitation? Contrasted examples from the Rhone Watershed

Background/Question/Methods

Floodplain lakes are specific features with a particular hydro-sedimentary functioning and ecological assemblages. They are considered by scientists, managers and decision-makers as unique environments within the temperate zone, possessing both high ecological and socio-economic values (biodiversity and refuge for fauna, flood attenuation, pollution buffering, providing recreational and educational opportunities). At river reach or site scale management practices (including rehabilitation) typically focus on one physical or human constraint yet they should be integrated as synergistic way to assess management efficiency. Using several examples from the Rhône watershed (Ain and Rhône Rivers, SE, France) we aim to illustrate how to combine socio-economical and eco-morphological objectives in floodplain lake management to implement sustainable practices.
Results/ConclusionsEuropean LIFE program (i.e. a financial instrument supporting environmental conservation projects in Europe) successfully combined a floodplain lake and main channel rehabilitation project by excavating coarse sediments from infilled floodplain lakes and injecting in the main channel to prevent channel degradation, floodplain forest homogenization and to rehabilitate fish habitat. This project was a win-win outcome. The injection of locally derived sediment was economical and the floodplain beta diversity being improved by aquatic species recolonization in excavated lakes. However, when too many issues overlay or interact over a small area, management becomes difficult to promote actions that reconcile each of them. For example, along the lower reach of the Rhône River, a project was initiated to integrate eco-geomorphic rehabilitation and flood risk management. The idea is to enhance sediment reworking both for enlarging the flow capacity of the river during floods and for allowing new sediment depositions at low elevations for pioneer species conservation. However, this project was confounded by concurrent constraints such as increased bank erosion risk near cultivated areas, navigation and polluted sediment reintroduction. In such context, a scientific understanding should be hierarchally organized to achieve certain pragmatic objectives rather than try to reach a past reference condition. For this purpose, both societal wishes and potential functioning of targeted systems should be integrated. Societal wishes result from a complex combination of several aspects, such as risk management, to link lake rehabilitation but also public opinion about these environmental features. We also present results concerning how these lakes are perceived by the society and which kind of visual properties are positively evaluated. Lastly we discussed how potential functioning can be approached (or not) by historical and regional analyses.