Impact of the channelization-induced incision of the Skawa and Wis?oka Rivers, southern Poland, on the conditions of overbank deposition

The impact of river incision in response to channelization on the conditions of overbank deposition is shown by the study of two montane rivers from the upper Vistula drainage basin, southern Poland. The Wisl/oka River had insufficient energy to destroy the river-control structures and remained laterally stable in the course of the channel downcutting. Under such conditions, the incision has raised the relative elevation of the floodplain above the river bed, thereby reducing considerably the frequency of overbank flows, and increasing concentration of suspended sediment transport within the incised channel. On the high-energy Skawa, the long periods of incision of the channelized river alternated with the shorter periods of lateral channel migration over the twentieth century. This has led to the formation of an incised meander belt, within which flood flows are constricted, and where the high velocities of the floodplain flows inhibit overbank deposition. Field observations confirm an insignificant role played nowadays by floodplain sedimentation in the valleys of both rivers. This study shows that the potential of the floodplains of the Carpathian tributaries to the Vistula for sediment storage has been dramatically reduced over the few past decades as a result of the channelization-induced incision of the rivers. The frequency of overbank flows has decreased considerably on the rivers draining the eastern part of the Polish Carpathians, and the majority of the suspended sediment is routed within the resultant enlarged channels. In the western part of the mountains, high velocities of the floodplain flows restrict overbank deposition on the narrow floodplains developed along incised channels. Copyright © 2001 John Wiley & Sons, Ltd.