In result of a lew years' investigations or silting of small water reservoirs located in South Poland, intensity ofthe silting process as well as the granulometrie and chemical composition ofbottorn sediments were evaluated. The content of heavy metals i.e. copper, lead and cadmium was determined in samples collected in various parts or five small water reservoirs. The content of heavy metals was appraised according to the regulation of the Minister of Environment, according to the criteria or Polish Geological Institute, of Inspection lor Environmental Protection, of Institute of Soil Science and Plant Cultivation, and according to the Muller's method. The obtained results or determination of the examined heavy metals concentrations were compared with the values or reservoir and river sediment concentrations determined by other authors in Europe. Appraisal or sill quality, respectively to the adopted criteria, showed only an insignificant degree of pollution. Concentrations ofmicroclemcnts do not exceed the toxic concentrations for soils and environment bul may have a harmful influence on living organisms. Recording of changes or heavy metal pollution during many years' operation or small water reservoirs, considering changes occurring in the basins, requires continuation of investigations. It will enable to record changes or pollution during a longer period or operation or reservoirs, also against the background 01· changes occurring in river basins.

The aim of the study was to compare two grouping methods for regionalisation of watersheds, which are similar in respect of low flow and chosen catchments parameters (physiographic and meteorological). In the study, a residual pattern approach and cluster analysis, i.e. Ward’s method, were used. The analysis was conducted for specific low flow discharge q95 (dm3∙s–1∙km–2). In the analysis, 50 catchments, located in the area of the upper and central Vistula River basin, were taken. Daily flows used in the study were monitored from 1976 to 2016. Based on the residual pattern approach (RPA) method, the analysed catchments were classified into two groups, while using the cluster analysis method (Ward’s method) – into five. The predictive performance of the complete regional regression model checked by cross-validation R2cv was 47% and RMSEcv = 0.69 dm3∙s–1∙km–2. The cross validation procedure for the cluster analysis gives a predictive performance equal to 33% and RMSEcv = 0.81 dm3∙s–1∙km–2. Comparing both methods, based on the cross-validated coefficient of determination (R2cv), it was found that the residual pattern approach had a better fit between predicted and observed values. The analysis also showed, that in case of both methods, an overestimation of specific low flow discharge q95 was observed. For the cross-validation method and the RPA method, the PBIAS was –10%. A slightly higher value was obtained for the cross-validation method and models obtained using cluster analysis for which the PBIAS was –13.8%.