Functional river restoration as a lever for adapting to climate change from an interdisciplinary emblematic showcase on the Upper Rhine

Many large rivers have been regulated for navigation improvement, hydro-electricity production, agricultural development and flood protection. River regulation alters both aquatic and riverine habitat dynamics as well as ecological functionalities and ecosystem services. This study aims to evaluate the impacts of river regulation performed along the Rhine as well as climate change to develop a process-based restoration strategy for the Rhinau-Taubergiessen area. The study focuses on analyzing (i) planimetric changes of the fluvial landscape from 1778 to 2021, (ii) water level changes from 1830 to 2020 and (iii) groundwater level variations from 1925 to 2020. This study also investigates the distribution of fine sediment thickness and analyzes hydrological data from 1869 to 2020 as well as water temperature data from 1970 to 2020. The results reveal a significant decline in aquatic and riparian habitat dynamics due to river regulation, a reduced amplitude of groundwater table fluctuations, and a large reduction in flood frequency. At catchment scale, both alterations of the Rhine flow regime due to regulation works and global climate change - evidenced by a 2,9 °C increase in mean water temperature over the past 50 years - have been identified. Based on these findings, restoration strategies should focus on improving lateral connectivity by lowering bank dikes to increase flood frequency and duration, enhancing fluvial processes and reactivating surface-subsurface water exchange. This study highlights the importance of considering the effects of global climate change on restoration goals to improve the adaptation of restored ecosystems in these large-scale pressures.