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Article

Effects of Transverse Groynes on Meso-Habitat Suitability for Native Fish Species on a Regulated By-Passed Large River: A Case Study along the Rhine River

1
CNRS UMR 7362 LIVE, University of Strasbourg, F-67083 Strasbourg, France
2
CNRS UMR 5600 EVS, University of Lyon, Site ENS, F-69362 Lyon, France
3
Ecole Nationale du Génie de L’eau et de L’environnement de Strasbourg (ENGEES), École D’ingénieurs—Eau et Environnement, F-67000 Strasbourg, France
4
Électricité de France (EDF), Centre d’Ingénieurie Hydraulique (CIH), F-73370 Le Bourget-du-Lac, France
*
Author to whom correspondence should be addressed.
Water 2020, 12(4), 987; https://doi.org/10.3390/w12040987
Received: 28 February 2020 / Revised: 18 March 2020 / Accepted: 23 March 2020 / Published: 31 March 2020
(This article belongs to the Section Water Quality and Contamination)
River regulations ultimately degrade fluvial forms and morphodynamics and simplify riparian and aquatic habitats. For several decades, river restoration actions have been performed to recover geomorphic processes and diversify these habitats to enhance both river biodiversity and ecosystem services. The objective of this study is to provide quantitative feedback on the experimental restoration of a large regulated and by-passed river (the Upper Rhine downstream of the Kembs Dam, France/Germany). This restoration consisted of the construction of two transverse groynes and the removal of bank protection. A monitoring framework composed of topo-bathymetric surveys as well as flow velocity and grain size measurements was established to assess the channel morphodynamic responses and evaluate their effects on habitat suitability for five native fish species using habitat models. A riverscape approach was used to evaluate the landscape changes in terms of both the configuration and the composition, which cannot be considered with classic approaches (e.g., Weighted Usable Area). Our results show that the two transverse groynes and, to a lesser extent, bank erosion, which was locally enhanced by the two groynes, increased habitat diversity due to the creation of new macroforms (e.g., pools and mid-bars) and fining of the bed grain size. Using a riverscape approach, our findings highlight that the restoration improved eel and juvenile nase species due to slowing down of the current and the deposition of fine sediments downstream of both groynes. As a consequence, the restoration improved the habitat suitability of the studied reach for more fish species compared with the pre-restoration conditions. This study also demonstrates that the salmon habitats downstream of the restored reach were improved due to fining of the bed grain size. This finding highlights that, for restorations aimed at fish habitats, the grain size conditions must be taken into consideration along with the flow conditions. Furthermore, the implementation of groynes, while not a panacea in terms of functional restoration, can be a strategy for improving fish habitats on highly regulated rivers, but only when more functional and natural options are impossible due to major constraints. View Full-Text
Keywords: river restoration; large rivers; transverse groynes; geomorphic monitoring; riverscape approach; fish habitat models river restoration; large rivers; transverse groynes; geomorphic monitoring; riverscape approach; fish habitat models
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MDPI and ACS Style

Chardon, V.; Schmitt, L.; Piégay, H.; Beisel, J.-N.; Staentzel, C.; Barillier, A.; Clutier, A. Effects of Transverse Groynes on Meso-Habitat Suitability for Native Fish Species on a Regulated By-Passed Large River: A Case Study along the Rhine River. Water 2020, 12, 987. https://doi.org/10.3390/w12040987

AMA Style

Chardon V, Schmitt L, Piégay H, Beisel J-N, Staentzel C, Barillier A, Clutier A. Effects of Transverse Groynes on Meso-Habitat Suitability for Native Fish Species on a Regulated By-Passed Large River: A Case Study along the Rhine River. Water. 2020; 12(4):987. https://doi.org/10.3390/w12040987

Chicago/Turabian Style

Chardon, Valentin, Laurent Schmitt, Hervé Piégay, Jean-Nicolas Beisel, Cybill Staentzel, Agnès Barillier, and Anne Clutier. 2020. "Effects of Transverse Groynes on Meso-Habitat Suitability for Native Fish Species on a Regulated By-Passed Large River: A Case Study along the Rhine River" Water 12, no. 4: 987. https://doi.org/10.3390/w12040987

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