REGULATED RIVERS: RESEARCH & MANAGEMENT Regul. Riers: Res. Mgmt. 15: 231–244 (1999) RESTORATION OF FLOODPLAIN RIVERS: THE ‘DANUBE RESTORATION PROJECT’ FRITZ SCHIEMER a, *, CHRISTIAN BAUMGARTNER a AND KLEMENT TOCKNER b a Uniersity of Vienna, Institute of Zoology, Department of Limnology, A-1090 Wien, Althanstraße 14, Austria b Department of Limnology, EAWAG/ETH, CH-8600, Duebendorf, Switzerland ABSTRACT 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 perspec- tive — differ strongly according to the degree of anthropogenic changes. This requires precisely formulated ameliora- tion 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 experi- ments 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. KEY WORDS: Danube; floodplain; river – floodplain INTRODUCTION The emerging concept on the ecological restoration of large rivers builds on a few general principles: (1) the restoration approach should be based on theoretical concepts of river ecology, (2) it should be process- (ecosystem-) orientated instead of species-focused, and (3) restoration should primarily foster the hydrological and geomorphological functions of the river (‘let the river do the work’) (Regier et al., 1989; Gore and Shields, 1995; Henry and Amoros, 1995; Sparks, 1995; Stanford et al., 1996; Ward et al., 1999). The consensus is that rehabilitation should ideally be conceived at a catchment scale. The scope for basin-wide improvements is, however, restricted with the possible exception of improving longitudinal migration routes and biogeographic corridors. On the other hand, there is immediate need for river – floodplain integration at a meso-scale in order to improve hydrological connectivity and ecological conditions along individual river segments. The formulation of protocols for specific river amelioration programmes raises many questions with regard to the feasibility, opportunities and constraints of different scenarios (Dahm et al., 1995; Stanford et al., 1996). In addition, there is an urgent need to develop a monitoring concept that allows the success of programmes to be analysed and evaluated (Schiemer, 1994). At the same time, well-planned restoration schemes offer a unique opportunity for large-scale experimen- tal tests of theories of river ecology (Bayley, 1995). This is the first in a series of three papers in which the authors present the concept and report on experiences gained in the planning and pre-implementation phase of a floodplain amelioration programme for the Austrian Danube. In this introductory paper, we present some general characteristics and limnological features of the Austrian Danube and describe the main impacts of river regulation over the past 120 years. The resultant ecological repercussions and trends in the regulated but free-flowing zone are briefly outlined based on two floodplain segments, with distinct states of disconnection, ‘Lobau’ and ‘Regelsbrunn’; restoration schemes for these two segments have already been developed and are currently * Correspondence to: University of Vienna, Institute of Zoology, Department of Limnology, A-1090 Wien, Althanstraße 14, Austria. CCC 0886–9375/99/010231 – 14$17.50 Copyright © 1999 John Wiley & Sons, Ltd.