Restoration of alluvial dynamics in the Old Rhine River (Kembs Dam): Favorable Outcomes Despite Limitations to Upscaling Caused by Old and New Pressures

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The 2010 renewal of the Kembs hydroelectric concession (France, along the Swiss and German borders), was the starting point of a vast project aimed at restoring alluvial dynamics and typical regional biodiversity, consisting of: environmental flows, gravel injections (66,000 m3 ), controlled erosion processes (1 km), re-establishment of connectivity (fish, aquatic mammals) and the recreation of a watercourse (“Petit Rhin”) flowing through 100 ha of restored, formerly cultivated land on Kembs Island (a former branch of the Rhine perched on an alluvial terrace). Monitoring results (2008 to 2020) show extremely high gains in biodiversity (taxonomic richness and heritage taxa) of all groups (flora, insects, amphibians, mammals, fish, etc.), related to the Kembs Island restoration. This new annex of the Old Rhine now plays a role locally as a biological reservoir, and regionally for the reproduction, feeding, or resting of various migratory and non-migratory fauna (birds, bats, insects …). Local-scale restoration of alluvial connectivity typical of land-water boundaries was possible, resulting in a diversification of functional environments necessary for typical Rhine species. However, large scale restoration would require continuous, largevolume gravel injections and a major widening of the Rhine riverbed; requiring consideration within a broader framework of territorial projects in association with all stakeholders. Beyond the legacy of hydromorphological pressures, aquatic species recovery was strongly constrained by chronic toxic pollution of the Rhine, and especially by recent biological invasions. Complex restoration projects must account for legacy and novel factors and their synergies/antagonisms to determine the most cost-effective measures for biodiversity.

Resource Type:
Conference Presentation, SER2021

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