Abstract
Abstract A major part of Poland, classified geographically as Polish Lowland, is covered by a layer of loose or cohesive sediments whose thickness increases toward the north. Numerous authors emphasize the impact of the protrusion of the erosional base level on the course of processes shaping modern river valleys. It has been demonstrated, among other things, that the culmination of the sub-alluvial, cohesive bedrock determines the manner in which the channel zone and the adjacent floodplain are formed, which is associated with the hydrological system of the river. A number (12) of geological documenting holes have been drilled to the bottom of the valley. Also, geological profiles were recorded for 34 natural outcrops. The range of the individual outcrops was determined using a geomorphological analysis based on, among other things, the data from airborne laser scanning. The main objective of the research based on geomorphological criteria was to identify the differences in valley morphology and geological structure as well as the dynamics of currently occurring fluvial processes, along with geological features influencing their development, in particular in the middle course of a river. The research allowed the distinction of three geologically and geomorphologically characteristic sections. This allowed an answer to the question: why is the river in the lowland similar to a mountain stream.
Highlights
In the landscape of lowland areas, river valleys are forms with the highest dynamics of morpho- and lithogenetic processes
The work involved the implementation of photo documentation of the channel area and the adjacent terraces as well as the drilling of 12 shallow boreholes documenting the geological structure of the river channel substratum
The presented research allowed the distinction of valley sections differing in several aspects: the shape of the valley, the nature of terrace surfaces, the geological structure of the valley substratum and its slopes, and the supply of clastic material
Summary
In the landscape of lowland areas, river valleys are forms with the highest dynamics of morpho- and lithogenetic processes. In Polish Lowland, the specificity of the geological structure of individual sections of the valleys results from the morphogenetic immaturity of river valleys [4,12] and the complexity of evolutional processes in their bottoms (occurring since the end of the Pleistocene) [2,4,5,13]. This is caused by the Pleistocene history of the analyzed area, including the glacial–interglacial rhythm of climate changes [14].
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