Boundary conditions of morphodynamic processes in the Mura River in Slovenia Lidija Globevnik a, ⁎, Matjaž Mikoš b, 1 a Institute for Water of the Republic of Slovenia, Hajdrihova 28c, Ljubljana, Slovenia b University of Ljubljana, Faculty of Civil and Geodetic Engineering, Jamova 2, 1000 Ljubljana, Slovenia abstract article info Available online xxxx Keywords: Granulometry Gravel-bed river Mura River River sediments River morphology Many alpine gravel-bed rivers have been altered in the past due to human interventions. A typical transboundary alpine river in Central Europe flowing over Austria, Slovenia, Croatia and Hungary is the Mura River (length: 465 km, catchment area: 14,304 km 2 ). The main problem of the river before leaving Austria is bed degradation (average 0.5 m from 1970 to 2000) as a combined consequence of river regulation works and the reduced sediment supply from the upstream reaches due to the construction of hydro power plants. River restoration measures for the river reach on the border between Austria and Slovenia (SLO–A Mura reach) were proposed in 2000 to support both ecological and flood protection purposes that apply the concept “of self-restoration”. In order to apply similar process-oriented restoration strategies in the Mura River downstream in Slovenia, we consider the potentials for self-forming river processes. We have analysed the sediment granulometry and morphology of the Mura River in Slovenia, and discussed morphodynamic processes to detect potential for the Mura River recovery into a more diverse morphological structure. The cross section area increased by 8% between 1979 and 2005 on average, mainly due to riverbed degradation. On average, the thalweg of the Mura riverbed in Slovenia had degraded by 0.28 m in the 1979–2007 period, with the highest degradation of 2.28 m in one cross section and some cross sections being stable. The high river degradation trend from the SLO–A Mura reach is slowly shifting to the downstream direction into the Mura River in Slovenia. Nevertheless, the clear downstream coarsening of river sediments turns into the normal trend of sediment fining in the Mura River reach in Slovenia. The “self-restoration” potential in the Mura River reach in Slovenia is larger than on the SLO–A Mura reach due to still active morphological fluvial processes. These processes can be enhanced by the inflow of fresh coarse sediments from the SLO–A Mura reach, where active measures for re-establishing sediment transport are under way. In the long term, this will not work as proposed, if no sediment inflow is re-established from the Mura headwaters in Austria. © 2009 Elsevier B.V. All rights reserved. 1. Introduction In the European Alps, every larger river system is anthropogenically influenced; many rivers have already reached or will soon reach a critical state of morphodynamic development (e.g. river bed break through its own alluvium into older deposits), where “natural” river restoration will be almost impossible. On such sections, the sediment transport and river morphodynamics play a central role in river restoration and need to be incorporated, including floodplain restoration. Besides, a link must be drawn between the past and the future with respect to restoration actions. Implementing the European Water Framework Directive will promote river restoration, the goal being to reach good ecological status of running waters by 2015. Beside ecological parameters (e.g., composi- tion, abundance, and age structure of the fish fauna), hydromorpholo- gical variables should be also included in the implementation of the WFD to evaluate the development of rivers and to react promptly to critical trends. Furthermore, a scale-oriented approach has to be developed to practically implement river restoration, including scaling (from the catchment-wide scale to the point scale). Within the framework of WFD implementation in Slovenia, 155 surface water bodies were determined in 2005 (Globevnik et al., 2006), out of which 22 were classified as candidates for heavily modified water bodies. Four candidates of the heavily modified water bodies on rivers are on the Drava River (Inštitut za vode Republike Slovenije, 2006). Along the Drava River, the largest river in Slovenia, a chain of hydro- power plants had been built in the 20th century. However, there are no hydropower plants on the Mura River, the Drava River tributary. It is predicted that there is a low risk that good ecological status of the Mura River in Slovenia will not be attained by 2015 (Globevnik, 2007). Nevertheless, the risk has been evaluated on the basis of its present chemical and hydromorphological status. No past and possible future hydromorphological processes, as governed by its Alpine character, have been considered so far. The Mura (Mur) River is a Central European river, springing at 1898 m a.s.l. in the Eastern Alps in Austria. The Mura River is the Catena xxx (2009) xxx–xxx ⁎ Corresponding author. Fax: +386 1 4624162. E-mail addresses: lidija.globevnik@izvrs.si (L. Globevnik), matjaz.mikos@fgg.uni-lj.si (M. Mikoš). 1 Fax: +386 1 2519897. CATENA-01452; No of Pages 12 0341-8162/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.catena.2009.06.008 Contents lists available at ScienceDirect Catena journal homepage: www.elsevier.com/locate/catena ARTICLE IN PRESS Please cite this article as: Globevnik, L., Mikoš, M., Boundary conditions of morphodynamic processes in the Mura River in Slovenia, Catena (2009), doi:10.1016/j.catena.2009.06.008