The paper assesses the usefulness of various methods for calculating the loads of pollutants washed out of an agricultural catchment. The data used in the study concerned the Mała Wełna river catchment in the hydrological years 2000-2005. The actual values on the day of water sampling and the mean monthly values of water flow were positively correlated (significantly at ? = 0,05) with the concentration of nitrate nitrogen. The relationship was most accurately described with polynomial regression equations. The daily concentrations of nitrates, calculated from the equations, and the daily water flows were used to compute the daily loads which were then treated as a reference. Next, the calculation was made using seven statistical methods, the results were analysed in detail, and a suitable algorithm was selected for computing the annual load at rare measurements of pollutant concentration and frequent measurements of water flow (water levels). The results obtained by calculating the load as a product of the mean concentration of pollutants and the water flow from the interval between the water-sampling dates appeared to be closest to the mean of 2000-2005, computed by reference method (1.00 kg N-NO3 · ha-1 · year-1)

The variability of flow in two small lowland watercourses was studied in hydrological years differing in the pattern of meteorological conditions. It was found that the rate of water flow was lower in summer half-years than in winter halves. In some periods of the former, the flow disappeared. Such periods were longer for a smaller, 100% afforested catchment. There were significant differences in unit discharges to the advantage of the larger catchment with a twice lower forest cover index. Those might be attributed to the three times higher proportion of boggy sites in the forest area of this catchment.

In the years 1972-1989 and 1995-2005, water levels were recorded daily and water discharges were measured twice a month in a small stream running in the Odra river valley parallel to the river channel. The observations and measurements were made in three gauging sections: an outfall on the stream stretch fed from the river channel upstream of the damming weir, an outfall on the stretch drained by the river downstream of the weir, and a gauging section on a neighbouring stream not affected by the river channel. The study determined the mean annual and semi-annual (summer and winter) discharges and specific discharges. The results confirmed that the water levels in the river have a considerable influence on the discharge in the stream flowing through its valley.

An analysis of 69 undisturbed samples, taken from 18 genetic horizons of 4 soil profiles, was made to study the effect of the bulk density of soil on its saturated hydraulic conductivity. The relation between the two parameters for sandy soils was found to differ for that for loamy soils. Regression equations describing both relationships were worked out and characterised statistically. The measured values of saturated hydraulic conductivity were compared with the values computed using the Rosetta model. The model provided satisfactory results only for loamy soils. The studies confirmed the need for further research on local relationships between the basic, easily measured parameters of soil and its hydraulic parameters.

The investigations carried out in the estuary part of the Raba river focused on straight sand dunes shaping the river bottom. The following characteristics of the dunes were considered: height (H) measured at the highest rise of the crest, length (L) measured parallel to the flow, width (W) measured perpendicular to the length, and angle of the lee- -side and stoss-side slopes. Field studies included also the measurement of the depth of water (h) above the characteristic points of the bed forms. Using the data obtained, indexes characterising the shape (L : H, W : L) and the steepness (H : L) of dunes were calculated, and formulae describing the functional dependence of height and steepness, respectively, on length were developed. The geometrical parameters, i.e. length and height, of the forms were also related to the water depth.