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.

中文翻译：

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横流鱼对受调节的绕道大河上本地鱼类的中观栖息地适宜性的影响：莱茵河沿岸的案例研究

河流法规最终会降低河流形态和形态动力学，并简化河岸和水生栖息地。几十年来，人们一直在采取河流修复行动来恢复地貌过程并使这些栖息地多样化，以增强河流生物多样性和生态系统服务。本研究的目的是为一条大型受调节和绕过的河流（Kembs 大坝下游的莱茵河上游，法国/德国）的实验恢复提供定量反馈。这次修复包括建造两个横向槽和拆除堤岸保护。建立了由地形测深调查以及流速和粒度测量组成的监测框架，以评估渠道形态动力学响应，并使用栖息地模型评估它们对五种本地鱼类的栖息地适宜性的影响。河流景观方法被用来评估配置和组成方面的景观变化，这是经典方法无法考虑的（例如，加权可用面积）。我们的结果表明，由于新的宏观形态（例如，水池和中坝）的产生和对河床的细化，两个横向腹股沟以及在较小程度上被两个腹股沟局部增强的河岸侵蚀增加了栖息地的多样性。床粒度。使用河景方法，我们的研究结果强调，由于水流减慢和细小沉积物在两条河鱼下游的沉积，修复工作改善了鳗鱼和幼鱼种类。因此，与恢复前的条件相比，恢复提高了研究范围内更多鱼类的栖息地适宜性。该研究还表明，由于床粒尺寸的细化，恢复河段下游的鲑鱼栖息地得到了改善。这一发现强调，对于针对鱼类栖息地的恢复，必须考虑颗粒大小条件以及流量条件。此外，实施 groynes 虽然不是功能恢复方面的灵丹妙药，但可以成为改善高度管制河流鱼类栖息地的策略，