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Restoration concepts for large river systems are currently in an early stage of development. Possibilities for, and constraints of, rehabilitation—both from a process-oriented view as well as from the nature conservation perspective—differ strongly according to the degree of anthropogenic changes. This requires precisely formulated amelioration goals. Well-conceived and thoroughly analysed case studies are necessary to better understand reversibility, direction and time scale of changes, and the sustainability of various scenarios. It is important to plan controllable set-ups with long-term monitoring in the pre- and post-implementation phases of restoration programmes. In order to achieve these goals, monitoring instruments have to be developed and calibrated that allow the definition and analysis of improvements. Finally, controlled restoration programmes offer the opportunity for large-scale experiments to test overall concepts and hypotheses and have an important heuristic value to improve the understanding of river ecology in general. Copyright © 1999 John Wiley & Sons, Ltd.
Schiemer et al. (Fri,) studied this question.