20 A review on channel incision in the Polish Carpathian rivers during the 20th century

Abstract

Rivers draining the Polish Carpathians deeply incised over the 20th century and in many sections, the downcutting was especially rapid in the second half of the century. Incision has resulted from the increase in transport capacity of the rivers caused by their channelization, and the concomitant decrease in sediment supply to the channels. In some of the rivers, in-stream gravel mining has additionally reduced the amount of sediment available for fluvial transport. Where the rivers had insufficient energy to destroy the river-control structures and remained laterally stable following their channelization, bed degradation has proceeded at a relatively steady rate. On the high-energy rivers, the periods of incision of the regulated channel alternated with the periods of lateral channel migration following the destruction of channelization structures. The main phase of incision of the Carpathian rivers occurred progressively later in the upstream direction, this reflecting the variation in timing of the most intense channelization works along their course, the operation of upstream-progressing bed degradation as well as the concentration of the land use changes from the second half of the century in the montane parts of the catchments. A marked increase in flood hazard to downstream reaches and a reduction in the potential of Carpathian floodplains for sediment storage have been the most important detrimental effects of the river incision manifested at the regional scale. Changes in management of the rivers are necessary to reduce their transport capacity and re-establish the conditions for water and sediment storage on the floodplains.