The trends in the main thalweg path of selected reaches of the Middle Vistula River, and their relationships to the geological structure of river channel zone

Abstract

Research carried out by the authors’ team in the valleys of many rivers in the Polish Lowlands has shown that the contemporary morphodynamics of channel zones is highly influenced by protrusions of erosion-resistant sub-alluvial bedrock. The article presents the results of analysis of two reaches of the Middle Vistula: near Solec nad Wisłą (km 330-340) and Gołąb (km 382-388), where such protrusions have been found. At each of them, two series of bathymetric measurements were carried out during medium and low water levels in the river channel. The measurements were made using hydrographic sets integrated with a GNSS receiver. The first series of measurements was carried out in July 2004, and the second one in September 2016. In parallel with the bathymetric surveys, low-altitude aerial photographs were taken in 2016 to document the morphology of the channel zone and the condition of the river engineering structures. A comparison of the obtained bathymetric maps shows a high correspondence between the thalweg line from 2004 and that observed twelve years later. This phenomenon proves the significance of the bedrock relief beneath the modern alluvial deposits for the water flow process in the channel. The relief causes the flow to concentrate in specific zones so strongly that it contributes to the damage of river engineering structures that put limits on the channel processes. This trend of concentrating the main thalweg is also accompanied by the diversity of depositional environments of river channel facies, identified along the studied reaches.

Rivers Try Harder. Reversed “Differential Erosion” as Geological Control of Flood in the Large Fluvial Systems in Poland

“…1% of 1069 sheets is unpublished yet) of The Map, the 20 of these sheets revealed the geological cross-section presenting the discussed pattern [11][12][13][14][15][16][17][18]. The pattern is known from previous studies which were based mainly on fieldwork [11][12][13][14][15][16][17][18]. These 20 cross-sections were split into 6 groups.…”

“…The results of previously published studies on this topic in a relatively small area (representing two large rivers in Poland [11][12][13][14][15][16][17][18]) indicate the existence of a specific geological pattern under the rivers flowing through the lowland landscape: the river prefers somehow to flow atop the bedrock protrusion.…”

“…Such a regional framework can develop a unique relation between the geological control of flood and the evolution of the fluvial system in Holocene. The relation is written in the geological pattern mentioned above [11][12][13][14][15][16][17][18]. This specific pattern looks opposite to: (i) the pattern expected from the differential erosion, and (ii) the pattern found in a typical lowland river valley where fluvial deposition increases downstream.…”

“…The existence of the specific pattern [11][12][13][14][15][16][17][18] should be verified in a larger area than the Vistula and Bug River valleys [11][12][13][14][15][16][17][18]. This is the main goal of our study: to determine the repetitive pattern of geological setting under large rivers (in the whole of Poland).…”

Natural and Geomorphological Response of the Small Lowland River Valley for Anthropogenic Transformation

“…Polish river valleys reflect the superimposition of many natural and anthropogenic conditions [20]. There are areas of the biggest intensity of the morphodynamical processes in Polish Lowlands, which results from reciprocal impacts of hydrological and geological factors [14,[20][21][22]. The relief of river bottoms and their bank zones (the proximal part of the floodplain) is constantly changing, causing the disappearance of some habitats and the development of new ones, so the valley biotopes are at different stages of succession and sometimes undergo partial or total degradation.…”