Nauka Przyroda Technologie

Abstract. The main aim of the paper is the analysis of reasons for spatial variations in suspension concentration, composition and grain distribution in the highly discharged Włocławek dam reservoir. The research results show that in the upper-river part of the reservoir requirements of the river suspension supplies are decisive in the turbidity course. In the low-water discharge conditions this is the sandy and coarse grained silt fraction suspension with the source in the riverbed bottom deposits. In the periods of a higher discharges is observed a transport of the fine grained silt suspension delivered from the eroded banks of the river channel. In the lower-lacustrine part, the size and features of the suspension concentration depend mainly on the intensification of hydrodynamic and sedimentological processes taking part in the reservoir water mass. The suspension mainly consists of the coarse grained silts. Under a slow stream flow circumstances the sandy fraction and aggregated clay particles are deposited. Additional source of fine- and coarse grained silt in a time of intensive reservoir water mixing are the bottom sediments. Periodically higher concentrations of suspension taking place in the lacustrine versus the river part of the reservoir are a big scale consequences of the deposits turbidity and resuspension processes in the Włocławek Reservoir.