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Anthropogenic changes in the suspended..

1987; Babiński and Klimek 1990; Babiński 1992; Łajczak 1995a). The shortening, deepening and narrowing of the channel has resulted, on average in a two-fold increase in the flow velocity of the Upper Vistula. The end product of this is a much-enlarged bankful discharge of this river stretch, possibly as much as three-fold compared with pre-regulation times (Łajczak 1995a). A much larger load, including sand and gravel originating from continuous channel deepening, was thereby created and this sediment was transported over longer distances than previously,

3) Lastly, the decreasing trend in the river load which was first noted about 1920, and which was later intensified. The increasing number of dams within the river catchment (which trap large amounts of incoming load), changes in land use (afforestation), the gradual disuse of the numerous cart roads on the flysch slopes in mountain areas, and a significant reduction in downcutting rates in some stretches of the Vistula which started about 1950, are all considered to be factors responsible for this.

Thus, man’s impact on fluvial processes in the Vistula have to some extent both enlarged and diminished the river load. Figurę 2 shows the relative changes of selected factors which have influenced the transportation by and sedimentation rates of the river, all of which have occurred in the last millennia.

Until now, only data relating to the changes in sedimentation rates which have occurred in the Vistula valley during the first phase of Man’s impact on fluvial processes, have been available (Maruszczak 1982; Starkel 1983, 1988, 1990, 1995; Klimek 1987, 1988; Gębica and Starkel 1987; Kalicki and Starkel 1987; Pożaryski and Kalicki 1995; Kalicki 1996). Also, the increasing rates of sedimentation at certain places on the valley floor which occurred before the end of the 19th cen tury have been analysed by Falkowski (1975, 1982). By contrast, we have few details of the long-term changes of river load and sedimentation rates of the Vistula during the second and third phases. In this case, the following ąuestions are particularly pertinent:

—    what is the role of river channel regulation in long-term changes in the transportation rates, and in the spatial distribution of sedimentation rates?

—    what is the role of the dam on the Vistula and its tributaries in respect of sediment trapped in reservoirs and in the reduction of sediment supply to the Vistula downstream of these barriers?

—    what are the outflow rates due to reservoir shallowing, flushing and dredging practices over long periods?

—    in the light of further dam construction, what is the prognosis for sediment input to the Vistula from its various tributaries, and also that to the Baltic Sea via the Vistula over long time periods?

The aim of the paper is to assess quantitatively the anthropogenically-induced changes in the transportation and sedimentation rates of the Vistula. It focuses on the effects of channel regulation, dam construction and reservoir exploitation.