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Vistula valley between the outlets of Dunajec and Breń

The Vistula river preserved its meandering naturę in the discussed section, or at least in some fragments of this section, until the 17th cen-tury. The abandoned channel to the south of Nowy Korczyn was un-doubtedly active at that time as indicated by the map of Michałowski (1678). Then, the Vistula was the river of variable discharges and of a relatively fast migrating channel which is evidenced by the traces of migration visible in the abandoned channel area and sometimes by a channel anabranching. The presence of silty, slightly sandy madas on the bar of one of these abandoned channels is interesting. That would confirm the ppinion of Szumański (1982) that it is a young sediment form-ed during the last centuries.

The change from the meandering to the straight river took place at the tum of the 17th and 18th centuries, i.e. earlier than in the San valley (mid-18th cen tury) or in the upper reaches of the Vistula (Szumański 1982; Trafas 1975; Rutkowski in press).

An increase of the supply of the slope materiał due to a farming in-tensification, and particularly an introduction of root crops (Gil, Słupik 1972), is considered to be the major cause of changing of the naturę of the rivers in the Sandomierz Basin. The former change of the river pat-tern in the discussed section may be resulted from this section location below the Dunajec outlet. One has to remember that the Dunajec is the river of very variable discharges and rapid floods. It drains the large area what results in the supply of ca. 1/4 of the water flow to the Vistula during the freshet periods while the 17th century increase of the flood freąuency could have played here a fundamental role.

The maximum horizontal channel shift reached 800 m during the last 200—250 years. The formation of the youngest flood plain (III) is also related to the above changes. The flood plain cover was packed into the elder deposits, presumably originating, at least fragmentarily, of the Last Glaciation.

The present Vistula channel downstream of the Dunajec outlet is almost totally enforced artificially and large amounts of the anthropo-genic pollutions are transported in it. The channel does not exhibit ero-sional tendencies. The sediment supply to the channel can increase in the futurę due to destruction of the willow thickets and due to formation of arabie fields in the interembankment area.

Technical University of Mining and Metallurgy Institute of Geology and Minerał Deposits 30-059 Kraków, al. Mickiewicza 30