The Impact of Bridges on the Process of Water Turbidity on the Example of Large Lowland Rivers

The transformations of river channels as a result of human activity may reflect the level of anthropogenic pressure. Recorded in macroscale, they are indicators of transformations for the larger part of the river basin, while in the microscale they usually refer to its fragment. The human activity that has the strongest influence on the fluvial processes, including suspended sediment transport, is the interference in the riverbed, such as hydrotechnical construction (create of water stages) or transformation of the river banks (concreting of the river banks). The aim of the research was to determine the impact of bridges on the process of water turbidity in the longitudinal profile of large lowland rivers. The research area was the lower reach of Vistula – bridge profiles: Torun, Bydgoszcz, Kiezmark (Poland) and bridge profile on Sukhona – a tributary of the Northern Dvina River near the city of Veliky Ustyug (Russia – Arkhangelsk Oblast). The research conducted in the years 2013–2017 included the measurements of water turbidity in the cross-sections of the above-mentioned rivers. The determinations of water turbidity were carried out using traditional (granulometry analysis) and nephelometric methods (devices: LISST-25X and turbidimeter). The impact of bridges on the variability of water turbidity was determined. The obtained results were related to the variability of depth conditions (bathymetric measurements) and hydrodynamics in the cross-section profile of the channel.