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A. Łajczak

1987; Klimek 1987, 1988; Dai 1988; Babiński and Klimek 1990); they are accelerated by mining, urbanization and, especially, river channelization and dam construction (Wolman 1967; Walling 1974; Klimek 1987; Knighton 1989, 1991; Klimek and Macklin 1991; Babiński 1992; Łajczak 1995a).

Changes in fluvial transportation and sedimentation rates can be estimated either on the basis of suspended load measurements and repeated river cross-section levelling (during recent decades), or by field measurements of the thickness of the newly-formed overbank sediments. Both methods permit the recognition of the periods which have morę intensive fluvial transportation and also provide for quantitative determination of the present-day changes in that transportation.

STUDY AREA

The Vistula River is 1047 km long, drains an area of 194,424 km² and has a mean discharge at its mouth of 1250 m³s^_1. It flows throughout several areas with very varied suspended sediment loads. Suspended matter constitutes ca. 65—70% of the mechanical work performed by the river; variations are recorded daily at 16 gauging stations on the river and at 69 gauging stations on its tributaries (Fig. 1). Recording began as early as the 1940s—1950s. The Carpathian part of the drainage basin produces the largest amount of suspended load input to the river (Łajczak 1995a).

The history of man’s impact on the transportation by and sedimentation rates of the Vistula may be characterized thus:

1)    The first long phase, typified by increased transportation and sedimentation rates, started before the Bronze Age and continued well into the second half of the 19th century (Starkel 1983, 1988; Gębica and Starkel 1987; Kalicki and Starkel 1987; Klimek 1987, 1988; Szumański and Starkel 1990; Pożaryski and Kalicki 1995). The river channel became much shallower and wider and, downstream of mouth of the San tributary, it changed into a braided system (Falkowski 1975, 1982; Maruszczak 1982; Sokołowski 1987; Babiński and Klimek 1990),

2)    The river training works sińce the middle of the 19th century: river length shortening (19th century), the building of stone groynes for river channel narrowing (sińce the middle of the 19th century), the construction of embankments for flooded area narrowing (sińce the end of the 19th century), the building of bedload trap dams on streams in the Carpathians (sińce the 19th century), the building of dams on the river and its tributaries (in the Carpathians especially) (sińce the 1920s), typify the second phase.

These regulation works initiated swift changes in river channel morphology which have subseąuently tended towards a new state of eąuilibrium in the channel. One conseąuence was that the channel of the upper and lower stretches of the river was subjected to fast downcutting, typically now about 1-2 m on average, and as much as 4,5 m near Cracow (Punzet 1978; Klimek