27 River restoration in the Alps and their surroundings: past experience and future challenges

Abstract

Alpine 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-transport-dominated conditions must include the full spectrum of scales, striving to initiate self-forming 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.

Introduction

In Europe, all large rivers have been significantly modified by human activities for centuries (Petts, 1989). A study of the International Commission for the Protection of the Alps (CIPRA) showed that only around 10% of the most important rivers of the entire Alpine region are still “pristine” or in a “near-natural” condition (Martinet and Dubost, 1992). The earlier activities concentrated on local works for flood and bank erosion protection but also for navigation purposes. The basic river morphological features underwent serious disruptions in the 19th century, when systematic hydraulic engineering measures were conducted along reaches of 1 to more than 100 km length. These major and widespread regulation efforts totally modified the morphodynamics and sediment transport behaviour, initiating channel changes such as river-bed degradation (Habersack and Nachtnebel, 1995; Bravard et al., 1997). These morphological changes led to abiotic and biotic consequences, and are associated with ecological and economic impacts (Roux et al., 1989; Bravard et al., 1999a; Jungwirth et al., 2003). Today's critical situation in terms of management (channel instability problems, limitations of flood regulation works, biodiversity decrease) has made river restoration a major issue in the Alps and their surrounding areas (Bravard et al., 1999a; Gilvear, 1999). These efforts are reinforced by the European Water Framework Directive (WFD), which aims to ensure that rivers will reach good ecological status by 2015 (European Parliament and Council of Europe, 2000). The first step in addressing these concerns is to describe the existing situation. This incorporates a deficit analysis, which highlights the risk that a certain water body will not reach a good ecological status by 2015. This is followed by a planning phase. In the final phase, measures are implemented to reach the goal. To date, no formal guidelines for restoration are available to achieve these goals. This calls for a summary of current measures in order to evaluate the most appropriate applications.

In the Alpine environment, high gradients generate significant energy and channel features are sensitive to changes in control parameters (peak flow regime and bedload input). A key challenge in river restoration is to identify the processes and primary parameters with which to improve both geomorphological and ecological conditions, under often-restricted boundary conditions (Jäggi, 1989; Bravard et al., 1999b; Piégay and Schumm, 2003). Early attempts at river restoration mainly applied small-scale measures. However, successful restoration projects in high-energy and bedload-transport-dominated conditions have to emphasise the full spectrum of scales, striving to initiate self-forming morphodynamics (Amoros et al., 1982; Frissell et al., 1986; Amoros and Petts, 1993; Habersack and Nachtnebel, 1995; Habersack et al., 2000).

In this context, we present the historical evolution of rivers in the Alpine area and their surroundings, and discuss how this evolution has led to the necessity of river restoration. A summary of restoration experiences is then drawn. Feedback elements are provided to explain such actions and their limitations, highlighting research challenges.