Complex transformation of the geomorphic regime of channels in the forefield of the Moravskoslezské Beskydy Mts.: Case study of the Morávka River (Czech Republic)
Introduction
The research on river system development over time has paid significant attention to the identification and determination of the processes causing the river changes (Brierley et al., 2006, Gregory, 1977). The state of contemporary channels has been particularly determined by the development since the end of the Last Glacial characterised by anthropogenic impact, which started during the Neolithic revolution (Czudek, 2005, Ložek, 1973, Schumm, 1969, Schumm, 1977). In the last 100 years, European rivers have undergone distinctive changes in morphology (Bravard et al., 1997, Kondolf, 1997, Kondolf et al., 2002, Korpak, 2007, Kukulak, 2003, Lach and Wyżga, 2002, Landon et al., 1998, Liébault and Piégay, 2002, Rinaldi et al., 2005, Surian and Rinaldi, 2003, Zawiejska and Wyżga, 2010) that have unfavourable influence on both the neighbouring landscape and human activity. The most serious problems include channel transformation related to river pattern changes (Lach and Wyżga, 2002, Liébault and Piégay, 2002, Rinaldi et al., 2005, Wyżga, 1993, Zawiejska and Wyżga, 2010), progressive channel narrowing (Korpak, 2007, Liébault and Piégay, 2002, Rinaldi, 2003, Rinaldi et al., 2005, Surian, 1999, Surian et al., 2009, Surian and Cisotto, 2007, Surian and Rinaldi, 2003, Zawiejska and Wyżga, 2010) and incision (Kondolf et al., 2002, Lach and Wyżga, 2002, Marston et al., 1995, Martín-Vide et al., 2010, Preciso et al., 2011, Rinaldi and Simon, 1998, Rinaldi, 2003, Rovira et al., 2005, Surian and Cisotto, 2007, Surian and Rinaldi, 2003, Surian et al., 2009, Uribelarrea et al., 2003, Wyżga, 1993, Wyżga, 2001, Zawiejska and Wyżga, 2010).
The main reasons for the above-mentioned channel transformations are connected to the changes in sediment transport in the fluvial system from the so-called disconnectivities (Brierley et al., 2006, Fryirs et al., 2007a, Fryirs et al., 2007b, Hooke, 2003, Kondolf, 1997, Salant et al., 2012, Zawiejska and Wyżga, 2010), which are defined as discontinuities in the transfer of energy and material between two parts of the landscape system or the system as a whole (Fryirs et al., 2007a, Fryirs et al., 2007b). At present, the most dominant causes affecting sediment transport related to river bed changes in European rivers are related to artificial dams (Kondolf, 1997, Preciso et al., 2011, Surian, 1999, Surian and Cisotto, 2007), gravel extraction (Gob et al., 2005, Kondolf, 1997, Preciso et al., 2011, Rinaldi et al., 2005, Surian, 1999, Surian and Cisotto, 2007, Surian and Rinaldi, 2003, Zawiejska and Wyżga, 2010), channel regulation (Preciso et al., 2011, Rinaldi and Simon, 1998, Surian, 1999, Surian and Cisotto, 2007, Wyżga, 1993, Zawiejska and Wyżga, 2010) and river basin land cover change (Gregory, 1977, Korpak, 2007, Kukulak, 2003, Lach and Wyżga, 2002, Liébault and Piégay, 2001, Liébault et al., 2005). The first three causes correspond closely to the period of the construction of valley dams, the beginnings of gravel extraction or river regulation and the beginnings of the acceleration of incision processes in channels (Liébault and Piégay, 2002, Surian, 1999). Beside sediment transport disturbances, valley dams significantly affect the runoff conditions (Fitzhugh and Vogel, 2010), which mainly concern the reduction of higher flood discharges that play an important role in channel transport conditions (Dolan et al., 1974, Lauterbach and Leder, 1969). The problems of land cover influence on bed-load conditions are hard to define because the response time related to sediment deficit/abundance in channels and the subsequent acceleration of erosion/accumulation processes is very long (Liébault and Piégay, 2002). Questions have arisen about the effect of land cover changes (i) in the whole basin and (ii) in the area of direct channel contact. In the first case, the question is related, for example, to the increased activity of debris flows whose delivery character is very important for the total sediment balance (Šilhán and Pánek, 2009), whereas, in the latter case, problems arise, for example, when the river banks lack stabilising vegetation as a result of water erosion (Graf, 1978). Another attributable cause of river system change is the effect of the climate fluctuations (Antonelli et al., 2004, Bravard, 2010, Liébault and Piégay, 2002) that greatly contributed to land cover changes as well as rainfall-runoff conditions.
The streams of the Czech part of the Carpathians demonstrate similar trends that have been described by a few minor studies (Galia et al., 2012, Hradecký, 2002, Hradecký, 2007, Škarpich et al., 2010, Škarpich et al., 2011). However, a more targeted study evaluating the impact of man on the river systems in this area is still missing. The main aim of this paper is to assess the morphological changes of the Morávka R. studied reach. In particular, the study concerns four basic areas: (i) river pattern change, (ii) active channel change in the last 200 years, (iii) the analysis of channel incision and (iv) a comparison of the Morávka R. transformation trends with other European rivers. A great deal of attention is also paid to the identification of the main causes of the studied local development in the context of contemporary changes.
Section snippets
Geographical settings
The Morávka R. is a gravel-bed stream with a length of 29.6 km that flows from the steeper Moravskoslezské Beskydy Mts. (MSB) to the relatively flat hilly piedmont (Fig. 1). The river bed is mainly composed of gravels with a median particle size (D50) of approximately 60 to 90 mm in the studied reach. The highest and lowest sites within the basin are, respectively, Lysá Hora Mt., at 1323 m a.s.l., and the mouth to the Ostravice R., at 386 m a.s.l.
The study area is the 13.5-km length river reach (with
Channel pattern
In fluvial geomorphology, the evaluation of the ground-plan changes of the development of rivers and river pattern is frequently based on the analysis of aerial and satellite images and historic maps (Gaeuman et al., 2005, Hradecký, 2002, Liébault and Piégay, 2002, Owczarek, 2008). In the case of the MSB, historic map analysis was used, namely (a) the Second Military Mapping from the years 1836 to 1852 at a scale of 1:28 800 (Fig. 5A) and (b) the Third Military Mapping from the years 1876 to
Channel-pattern change
The Morávka R. was used to be characterised by its branching pattern. The above-mentioned data indicate its wide channel and occasional migration of individual branches (Fig. 5A and B) along the whole studied reach (Fig. 1A), which is supported by aerial images from 1937 (Fig. 5C), where the wide channel void of vegetation indicates active channel migration. The photos also make it easy to identify some minor dry sub-channels with active migration and riparian vegetation in the vicinity of the
Discussion
Changes in fluvial systems are currently being investigated for many Europeans rivers, e.g., Alpine rivers in Italy (Preciso et al., 2011, Rinaldi and Simon, 1998, Surian and Rinaldi, 2003) and France (Liébault and Piégay, 2002, Liébault et al., 2005) and Carpathian rivers in Poland (Korpak, 2007, Wyżga, 2001, Zawiejska and Wyżga, 2010). Active channel changes in Europe are usually related to land cover changes and anthropogenic activities that started in 1950s and resulted in the blocking of
Conclusion
The state of contemporary rivers in the Czech Outer Western Carpathians has been particularly affected by development, starting at the beginning of the 16th century, with a significant anthropogenic impact during the so-called Wallachian colonisation. Extensive deforestation to clear pastureland and supply the demand for wood disrupted the original state of channels, which had been developing from the end of the Last Glacial period. The change in basin management related to the change in human
Acknowledgements
This research was supported by the project of the Czech Science Foundation No. GAP209/10/0309: ‘The effect of historical climatic and hydrometeorological extremes on slope and fluvial processes in the Western Beskydy Mts. and their forefield’ and by the project of the University of Ostrava Foundation SGS15/PřF/2013. Thanks are extended to Monika Hradecká and Elsevier Language Service for the English style corrections. We also gratefully acknowledge anonymous reviewers and editor for their
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