Summary:

The aim of this research was an assessment of impact of relocated Mała Wełna river channel on water conditions in the adjacent areas. In this paper also a fasibility to increase river flow capacity with the purpose of maintaining river channel dynamic equilibrium was presented. Field observations and measurements were carried out in hydrological years of 2000–2008 in Mała Wełna river catchment down to Kiszkowo crosssection. The main cause of valley flooding on the reach from Zakrzewo to Kiszkowo were hydraulic conditions at the relocated Mała Wełna river channel. The river cross-section geometry and its channel slope caused that at the high-water discharge SWQ the channel capacity of the river is too low. A lack of the river banks and bottom maintenance has had strong negative impact on the river capacity. To improve the river flow capacity and the drain ditches “A” and “B” it is necessary to make modernization of hydraulic structures and the whole water system in the catchment of the Mała Wełna river. Before this it is necessary to make a detail geodetic measurement of these areas.