Summary:

The muds settled in the Lake Dąbie have visco-plastic properties. They contain many organic matter and are polluted by sewage from communities and industry. The presence of this substances changes clearly the dynamic properties of the fine grained material, as well the conditions of sedimentation and resuspension of solid particles. An important navigation way is located in the lake Dąbie with following parameters: length 14.5 km, width 150 m and guaranteed depth 3.2 m. This way is periodically deepened by dredgers. The authors have performed a preliminary estimation of the physical and rheological features of mud samples from the Lake Dąbie in the region of the navigation way. The thickness of the mud layer is equal 3–5 m. The fine grined sediments have a liquid consistency, and their water content is equal to some 300- 500%. The nominal granulometric size d50 changes between 12–15 μm for superficial muds and between 44-95 μm for bottom muds, and the organic matter content varies between 10 – 30%. The studies on rheological features of organic sediments proved that they behave as non-newtonian liquids. Their behaviour can be described by the twoparameter rheological model of Bingham.