Flooded river valley meadows are very important for river ecology, as they entrap sediments and sediment-bound nitrogen or heavy metals. Nevertheless, the grass-covered floodplains, particularly in river deltas, are often separated from the rivers by dykes. When such systems are designed, it is necessary to model sediment deposition in these separated areas. However, the existing calculation methods and models are adapted for flow over the sandy bottom. In the meadow flows there are other boundary conditions more favourable for sediment deposition.

The focus of our studies was the processes of suspended sediment deposition in the flooded delta of the River Nemunas. Calibration results of the mathematical model with common sediment deposition formulae for riverbed flows did not correspond to the data of measurements. The differences were obvious. Consequently, it was necessary to study the peculiarities of flow and sediment motion under these conditions, as well as to work out formulae suitable for calculations.