Challenges in river restoration in the Alps and their surrounding areas

Book, SectionAlpine rivers have undergone significant changes over the two last centuries. Human activities have modified their geometry through engineering measures to gain land for agricultural purposes and settlements, as well as through active mining to exploit gravel resources. Their sediment and water transfers have also been altered by hydropower- plant construction, control works on high-gradient streams, and catchment land-use changes. The resulting river morphological changes have led to abiotic (e.g., river-bed degradation and narrowing) and biotic (e.g., longitudinal and lateral disconnection) disruption. The current critical management situation (channel instability problems, flood effects, biodiversity decrease) has made river restoration a major issue in the Alps and their surroundings. Such an approach is reinforced by the European Water Framework Directive, which aims to ensure that rivers attain a good ecological status by 2015. In the Alps, space is not always easily available and boundary conditions have changed over the long term. A major challenge in river restoration in the Alpine environment is therefore to identify the processes and key parameters for improving both geomorphological and ecological conditions under often-restricted boundary conditions. Early attempts at river restoration mainly focused on small-scale measures. Today, successful restoration projects in high-energy and bedload-transportdominated conditions must include the full spectrum of scales, striving to initiate selfforming morphodynamics. In this context, we appraise restoration experiences from the Alps, focusing on channel widening and dike enlargement, former channel reconstruction and reconnection, promotion of bedload supply input from floodplains, tributaries, and hillslopes, as well as on bank erosion measures and restoration activities. We discuss the basic arguments behind such actions, their limitations, and research challenges