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A. ajczak

and along particular river stretches. Particularly severely decreased rates have been recorded in the upper and lower stretches of the Vistula, where deep reservoirs on the river and its tributaries have been completed during the last few decades. The trend is independent of cyclic changes in the discharge of the river recorded in the past decades, and reflects only man’s impact. Only in that stretch of the Vistula upstream from Cracow did suspended load transportation and sedimentation increase markedly for a second time after the 1940s-1950s (Fig. 5), undoubtedly as the result of large coal dust supply from the wastewaters of mines in that region.

REFLECTION OF PRECIPITATION FLUCTUATIONS IN RIVER LOAD TRANSPORTATION BY AND SEDIMENTATION RATES OF THE VISTULA

Secondary changes in transportation rates of the Vistula, which consider-ably modify the decreasing trend for that transportation, occur in about

10- year and, additionally in the Upper Vistula, about 30-, 40-year fluctuations in sediment transportations. Adoption of 5-year running means of annual rates of that transportation has allowed for the discrimination of the periods which have increased suspended loads, which can easily be correlated with the fluctuations which have appeared in the mean and mean high discharges (Fig. 7). The 10-year fluctuations in discharge (to be approximated to the

11- year cycles of the Sun’s activity) are typical for large lowland rivers of Central and North-East Europę (Boryczka et al. 1992). Longer, i.e. about 20-, 30- and 40-year, fluctuations have not been identified in every river studied and the same situation seems to be true in the case of the large rivers of Western Europę (Probst 1989).

The fluctuations in the long-term plot of the mean high discharge of the Vistula are better correlated with fluctuations of suspended load transportation, when compared with the plot of mean discharge. The freąuency and size of the flood waves determine the rates of sediment transportation by the river; also, the total inundation time of the floodplain and, thirdly, the overbank deposition rates. Despite the obvious decreasing trend in inundation time of the floodplain being associated with deepened stretches of the channel, or of an increasing trend in the time when both channel stretches and floodplains are being aggraded, the recognized fluctuations to the inundation time of the floodplain are climatically controlled (Fig. 7). This explains the short cyclic changes in floodplain deposition rates, which are independent of man. According to Starkel (1983, 1988) the Holocene sedimentation rates recognized in the Upper Vistula valley are cyclic in 1000-, 100- and 10-year periods; they were climatically controlled and have intensified in historical time due to increasing human impact.