Geologiczne uwarunkowania dynamiki procesów brzegowych rzek zachodniego Podhala
Abstract
Geological controls on the dynamics of riverbank retreat in the western Podhale region.
A b s t r a c t. The western part of Podhale region is drained by the Czarny Dunajec and the Biały Dunajec rivers, flowing from the Tatra Mts., and streams originating in the region (Cichy Stream, Bystry Stream, Czerwony Stream, Wielki Rogoźnik). River banks are cut in the Podhale Flysch or in the alluvium of these rivers overlain with loam deposits of varied origin. This paper investigates the combined effect of weathering, frost processes and mass movements on the banks of the Czarny Dunajec River and its tributaries typified by different substrate material. Bank retreat due to frost processes was measured during multigelation periods using erosion pins. Grain size distribution and cohesion of the substrate were also determined for alluvial and loam deposits. On flysch cutbanks, we determined joint spacing and the density and direction of fractures, and other structural and textural characteristics of the rocks. The results indicate that the rate of bank retreat decreases from the banks cut in sandy loam deposits, through alluvial loam banks (with high clay content), the banks composed of poorly cemented gravels and shaly flysch, to the banks cut in sandstones and highly cemented Neogene gravels. Bank retreat due to frost processes and mass-wasting was more efficient in the cold half-year.
A b s t r a c t. The western part of Podhale region is drained by the Czarny Dunajec and the Biały Dunajec rivers, flowing from the Tatra Mts., and streams originating in the region (Cichy Stream, Bystry Stream, Czerwony Stream, Wielki Rogoźnik). River banks are cut in the Podhale Flysch or in the alluvium of these rivers overlain with loam deposits of varied origin. This paper investigates the combined effect of weathering, frost processes and mass movements on the banks of the Czarny Dunajec River and its tributaries typified by different substrate material. Bank retreat due to frost processes was measured during multigelation periods using erosion pins. Grain size distribution and cohesion of the substrate were also determined for alluvial and loam deposits. On flysch cutbanks, we determined joint spacing and the density and direction of fractures, and other structural and textural characteristics of the rocks. The results indicate that the rate of bank retreat decreases from the banks cut in sandy loam deposits, through alluvial loam banks (with high clay content), the banks composed of poorly cemented gravels and shaly flysch, to the banks cut in sandstones and highly cemented Neogene gravels. Bank retreat due to frost processes and mass-wasting was more efficient in the cold half-year.