Rates of frost erosion in river banks with different particle size (West Carpathians, Poland)

Abstract

An important process of river bank erosion is multigelation – alternating freezing and thawing of the banks caused by cyclical oscillation of ground temperature around 0 °C. This paper presents the results of studies on the influence of multigelation on stability of river banks in the Beskid Niski and at Podhale. Repeated measurements of scarp retreat on river banks (those composed of alluvium and those cut in bedrock) were conducted using erosion pins and sediment catchers for gravity-transported debris. The progress of erosion in time and amounts of eroded material were correlated with the record of temperature changes above ground. Multigelation resulted in significant modification of the studied river banks. Amount of erosion depended mainly on lithology and grainsize of the rocks composing the banks. The banks composed of fine sediments retreated in a uniform way and at a uniform rate over the whole surface. Progress of erosion of the banks composed of medium granels was selective. Finest sediment was loosened first. Then coarser clasts that lost suport, became detached and fell down. On the banks composed of flysch rocks, densely fractured shales were eroded first, followed by bigger fragments of sandstone layers. Frost erosion was the most intense on the banks built of fine gravels with clay matrix and the least intense on the medium-sized sandy gravels. Layers of alluvial clay were more resistant to frost erosion than fine and coarse gravels embedded in clay or sand.