Twentieth-century hydromorphological degradation of Polish Carpathian rivers

摘要

Case studies of the Sola, San and Dunajec rivers are used to demonstrate changes in planform geometry of the rivers draining the western and eastern parts of the flysch Polish Carpathians and those originating in the high-mountain Tatra massif since the second half of the nineteenth century. The number and width of low-flow channels and the length of river reaches are compared between the nineteenth-century and contemporary rivers, with analysis of other features of their planform geometry prevented by differences in the cartographic presentation of rivers on Austrian military maps and Polish topographic maps. In the second half of the nineteenth century, the rivers flowed in wide channels. The Sola supported a braided channel along its entire course, the Dunajec was mostly braided, with a single-thread channel within gorge sections, whereas for the San the braided pattern was limited to the reaches within intramontane and foreland basins. Over the twentieth century, the braided channel pattern was nearly completely eliminated and substituted by a single-thread pattern; multi-thread channel segments remained only in the upper course of the Dunajec River. Average low-flow-channel width significantly decreased, even by 66%, and this was accompanied by a reduction in the variability of low-flow channel width along the rivers. The change in planform channel geometry was accompanied by channel incision, which started earlier and has resulted in greater bed degradation in the foreland and foothill reaches of the rivers than in their mountain reaches. Twentieth-century river changes also encompassed a radical change in the facies pattern of channel sediments, accompanied by their coarsening and improved sorting and development of bed armour. Moreover, transformation of alluvial channel beds to bedrock ones took place in many reaches of Carpathian streams and rivers. The degradation of physical structure of Carpathian watercourses has resulted in adverse hydraulic and hydrological effects and a marked deterioration of habitat conditions for riverine biota. (C) 2017 Elsevier Ltd and INQUA. All rights reserved.