A Plea for the Restoration of Alpine Rivers: Basic Principles Derived from the “Rhone-Thur” Case Study

Hydropower use and settlement development adversely affected Alpine rivers and streams. The majority of Swiss and Austrian electricity is produced by hydropower plants, which impact the natural flow regime of running waters. In addition, channelization impairs the river morphology.

The resulting changes (alterations of the natural flow regime, lack of hydrological connectivity, deficits in morphology) significantly affect the ecology of rivers and streams, and cause major deficits. Restoration of hydrological connectivity and ecomorphological integrity is an urgent need for Alpine streams. The “Rhone-Thur” project developed guidelines for planning river restoration and formulated ten basic elements for carrying out successful projects. Inclusion of a reference system, baseline monitoring and a clear definition of project objectives are important steps at the beginning. The project scale and ecological improvements are also specified. Each successful project has to deal with the socio-economic aspects and include the stakeholders in an early project phase. Prediction of restoration measures and the alternative possibilities are helpful processes. After implementation, the core of each project is the evaluation of success and outcome. Comparison of appropriate indicator values before and after the restoration helps to classify the project objectives into different success categories: from failure to great success. However, great success is difficult to achieve and it is important to understand the outcome. Generally, river morphology recovers more quickly after restoration than biological communities (fishes) do. The degree of connectivity to intact neighborhood communities and the size of the restoration area influence the success of the restoration project. Possible restoration sites should therefore be prioritized within the watershed, and sites close to intact habitat with existing source populations provide higher success expectations. For Alpine ecosystems the restoration of a dynamic hydrological regime is a major task and a challenge for the future. This is mainly true for stream reaches with residual flow and river segments with hydropeaking problems.