Channel morphology changes and their relationship to valley bottom geology and human interventions; a case study from the Vistula Valley in Warsaw, Poland

The aim of the study was to determine the role of the geological setting of channel zone in the morphological variability of a river reach situated between engineered and seminatural channel sections. Investigations were carried out in the Vistula River channel in Warsaw. The study included the drilling of 60 geological boreholes in the river channel and the registering of sedimentary structures of modern river-channel sediments. The morphology of the channel was defined based on a series of bathymetric measurements of different river levels. To identify the reasons for the variation in the channel-bed morphology, numerical modelling of river flow was performed. Calculations were made using the FLUENT CFD (Computational Fluid Dynamics) model. The stabilization of bottom erosion along the engineered reach of the river was found to be associated with a shallow depth to the top of the basement of modern alluvial sediments, composed of erosion-resistant glacial deposits. The suballuvial basement in this part of the river channel also serves as a local base level in relation to the river reach upstream.