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T. Sokołowski

exceeds 20 km in some locations here. The valley is surrounded by pla-teaus, up to 100 m high, built of the Miocene clays (Sarmatian) covered with sandy and sandy-gravel glacial and fluvioglacial deposits of the South- and Middle-Polish Glacdations.

Foliowing Starkel (1972) the middle sandy terrace protruding several meters above the Vistula channel can be distinguished. That form in the interbasin of the Vistula and Breń rivers is called Garb Szczuciński by the above author. The terrace in ąuestion between Opatów and Nowy Korczyn is accreted by loesses on the left bank.

The lower valley bottom is occuppied by the terraces: rendzina one (the overflood terrace) with a mada cover at the top, and the flood plain (meadow terrace) — younger than the former one. These two forms are subjects of the present study (Fig. 1).

The Miocene clays occur in the substratum of the Quaternary alluvia, the latter building the discussed terraces. The relief of the terrace tops is very diversified (Fig. 2). The fossil valley bottom at the Dunajec outlet is almost fiat, and rises at the height 160—164 m a.s.l. Morę to the east, two almost parallel troughs, generally of the WE orientation, develop. They are separated to the east of Bolesław by a fiat ridge built also of the Miocene clays. It appears as well in the remote valley parts along the plateaus and below the loess terrace between Opatowiec and Nowy Korczyn. Similar socle, sometimes higher by 6—8 m, occurs near Olesno. That relief does not correspond to the present one. The middle terrace is developed both above the socles and above the troughs. The lower terraces appear mainly in a rangę of the northern troughs.

Moreover, these two troughs extend downstream the river and are increasingly pronounced, and in the area of Tarnobrzeg have been de-scribed by Mycielska-Dowgiałło (1978). Their continuation is in the trough stated in the lower reach of the Dunajec river (Sokołowski! 1981b).

The Vistula is the main river of the studied area. The tributaries are not without meaning for the valley modifications. The most impor-tant is the mountain river — Dunajec, especially during the floods. It influences a composition of alluvia, particularly of gravels, as well. The remaining tributaries are of the secondary importance due to their ma-gnitudes.

HYDROLOGICAL REGIME OF THE VISTULA

The gradient of the Vistula channel in the studied fragment of the Sandomierz Basin is 0.28%o what is a typical value of lowland rivers. The Vistula with the tributaries drains the area of 23 901 km* (up to the water gauge profile in Szczucin), the larger part out of which (43°/o) inclu-des the Western Carpathians, i.e. the area with mountain and upland tvpe relief. That is the region with precipitation of 700—1200 min/vv which