MAN`S IMPACTED CHANGES OF THE SEDIMENTATION COURSE OF THE SUSPENDED MATERIAL TRANSPORTED IN THE VISTULA RIVER BASIN, POLAND, IN THE 20TH CENTURY

Abrupt changes in intensity of erosion, transport and sedimentation of deposits are one of the effects of increasing human impact on river basins. The model of such changes described by numerous authors usually consists of two phases: abrupt increase of intensity of those processes and further decrease of the their tempo, often reaching the minimum value. Various regulation works and their geomorphological and hydrological effects have been described on the basis of the Vistula, the largest river in Poland. On that background, quantitative changes in amounts of transported suspended material in the river and its main tributaries in consecutive years after 1945 have been described. The "input-output" method has been used to estimate the amount of accumulation of the material within the inter-embankment zone of the river in the consecutive years since 1945. The results have been compared with the tempo of sediment thickness increasing outside the river course in the 20th century, which estimation has been based on repeated leveling taken by the State Hydrological Survey in successive gauging stations on the river across the inter-embankment zone, and the tempo of decrease of the volume of dam reservoirs. Calculated equations of regression describe the tempo of accumulation of sediments between the embankments of the Vistula River and in large dam reservoirs. In the inter-embankment zone of the Vistula River the rate of suspended material sedimentation has been decreasing since about 1930. While, in dam reservoirs, depending of their depth, the amount and the course of accumulation of suspended material have varied. The deep reservoirs have played the role of accumulators of sediments, while the shallow ones have temporarily played the role of exporters of sediments. Increasing role of deep reservoirs in permanent accumulation of the suspended material in the Vistula River basin has been proved, however, the main accumulator is still the area between the embankments, especially in the upper, piedmont course of the river.