Complex transformation of the geomorphic regime of channels in the forefield of the Moravskoslezské Beskydy Mts.: Case study of the Morávka River (Czech Republic)

Abstract

Abstract This paper presents a complex analysis of both the contemporary and the historic development of the geomorphic regime of the transformed reach of the Moravka River in the Czech Carpathians. The assessment concentrates on the conditions and causes of the channel development in the last c. 200 years compared with the state of European channels, especially those of the Carpathian zone. The Moravka R. pattern has undergone a rapid change in the last 50 years, particularly in connection with the active channel narrowing and massive incision. The original anabranching river pattern has gradually been replaced by a simple, narrowed channel incised into the bedrock. The average width of the Moravka R. active channel changed from 153 m in 1836–1852 and 165 m in 1876–1878 to 44 m in the year 2010. At some parts, the original river bed has lowered as much as 8 m in the last 40 years, which indicates an incision rate of 12–24 cm/year. These changes have been caused by strong anthropogenic impacts in the form of the river-channel control, bank stabilisation, and weir and valley dam construction. Other reasons are related to land cover and land-use changes. A great influence on the contemporary processes is also exerted by the geological predisposition of the Carpathian flysch lithology in channel bedrock, particularly the occurrence of claystone layers that present little resistance to water erosion. Currently, the deficit of transportable sedimentary material along with the increased transport capacity of the incised river bed has generated conditions for constantly intensifying erosion processes in the Moravka R. channel.