Effect of Emergency Water Discharges from the Dam in Włocławek on the Sedimentary Structures of Channel Bars in the Lower Flow Regime of the River Vistula

Abstract

Changes in the stream flow contribute to transformation of the river channel due to erosion and accumulation. Channel bars move as a result of water flow. This article presents the results of studies carried out on two channel bars formed in the River Vistula that were transformed during emergency discharges of water from the Włocławek reservoir. In order to present changes in structure and texture, pits were dug in the channel bars and samples were taken for grain-size analysis. The rate of migration of channel bars caused by emergency discharges was determined. Sedimentary structures were recorded as groups of strata indicating a variability in flow conditions (2D and 3D dunes, parasitic ripple marks, reactivation surfaces). It was observed that changes in the level of water and flow are reflected in sedimentary structures. The emergent channel bars are affected by aeolian processes that wear the flow marks off.