Aim of the study:
In this paper we attempt to determine the sediment flow conditions in the drainage system of the barrage in Łączany on the Wisła (Vistula) river. To this end, the distribution of suspended sediment concentration in the cross-sections of draining ditches was developed; the concentration profiles of suspended sediment in individual cross-sections of the main ditch were elaborated; and the assessment of the concentration variation in the concentration profiles in the determined cross-sections on the entire length of the main drainage ditch R in the drainage system Łączany was carried out.

Material and methods:
Four measurement cross-sections p-1, p-2, p-5 and p-7 were determined in the ditch R of the system, and three measurement cross-sections were determined on the tributaries to the ditch R. Point measurements of volumetric concentration of suspended sediment in cross-sections were conducted in accordance with the methodology of water sampling using bottle bathometers. Measurements were also made across the entire cross-section using a pre-calibrated Portable Suspended Solids Monitor 740 instrument produced by Partech company. The results of these measurements enabled the determination of the correction factor (k) for each of the measurement cross-sections.

Results and conclusions:
It was found that the values of this coefficient (k) range from 1.188 to 1.328, which means that in calculations of suspended sediment transport in the ditches of the drainage system, tested using the so-called normal method, it is necessary to take into account the variation of concentration of this sediment in the cross-section of the ditch. The differences in the volume concentration of suspended sediment in hydrometric divisions (verticals) were also found. These concentrations, measured in surface layers, regardless of the height of vertical filling, represented on average about 60% of the value of the concentration measured in bottom layers of the verticals, i.e. about 5 cm above the bottom.