The relationship between bank erosion, local aggradation and sediment transport in a small Carpathian stream

River bank erosion is the main process in small mountainous basins, especially those where the main channel is built of poorly resistant sedimentary rock or alluvium, exemplified by the Słomka basin.The main goal of the study, based on the field survey work and the erosion pin method, was to define the relation between river bank erosion, accumulation, and sediment transport.The investigations were carried out in the Słomka stream basin (watercourse length of 25.2 km, basin area of 69.9 km2) on an ~ 1.0-km-long stream reach, strongly anthropogenically transformed, between watercourse kilometres 5.0 and 6.0. We found that with an increase in flow the retreat bank rate increased nonlinearly. An average migration rate of the undercut banks ranged from 0.10 m for the flow rate of 11.5 m3 s− 1 to 0.92 m for the flow rate of 35.5 m3 s− 1. The maximum observed rate exceeded 0.8 m for the flow rate of 11.5 m3 s− 1 and 9.0 m for the flow rate of 24.8 m3 s− 1. With respect to the channel vertical morphology over the whole measurement section, we found that bed gradeline was raised, on average, by ~ 0.04 m. The trend is contrary to the results of field surveys performed earlier on the Carpathian watercourses. The phenomenon is related to the abundant supply of rock rubble into the stream channel.High flow stages in the Słomka stream, which caused the stream bed material to move, had a predominant impact on stream channel morphology. Processes such as destructive activity of rain drops, aeolian erosion (sandblasting), soil expansion, and shrinkage during the rainy and dry seasons were of minor significance.