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E. Niedziałkowska

2)    characteristics of both grain size and abrasion of the modern deposits and conditions under which such deposits occur in relation to the channel* comparison of modern deposits with the fossil ones;

3)    determinat ion of the course of sedimentation, especially that of channel fili deposits and of alluvial fan deposits.

This study is designed to show whether the two textural properties of f1uvial deposits, i.e. grain size and quartz abrasions, are dependent on the period of sedimentation or whether these were controlled by the geographical environ-ment.

The literaturę on textural properties of deposits (mainly grain size) is vast. In order to identify the different depositional environments, their typical features, and to reconstruct the palaeogeographical conditions of sedimentation (Vaśkovska 1971) grain size is usually analysed. Sometimes abrasion, heavy minerał content and petrographic composition of deposits also has been described. Based on the grain size and abrasion parameters are the attempts madę to reconstruct the long-termed palaeohydrodynamic conditions of rivers, as for example, during the Quaternary (Antczak 1986; Mycielska-Dowgiałło 1987).

A. Kostrzewski (1970, 1984), N. D. Smith (1974), B. M. Osovietskiy (1982), M. Church and R. Kellerhals (1978) and others argued that in the different terrace levels and channels both downstream grain size reduction and increase in the abrasion degree takes place. The fining of deposits which depends on the fluvial dynamics takes place by leaps. Essential grain size changes may not occur within one geomorphological zonę.

Another approach (Folk, Ward 1957; Bridge 1978; Levey 1978; Nanson 1980; Bridge, Jarvis 1982; Eschner and Kircher 1984) has been concerned with relating the analyses of both grain size and sedimentary structures to direct observations and water flow measurements madę in selected channel sections. The purpose of observations and experimental studies is to help explain the role of processes of both abrasion and morphoselection under different hydrodynamic conditions prevailing in the channel (Kaniecki 1975; Młynarczyk 1985).

THE STUDY AREA

Both catchments contain remarkable contrasts in the geographical environ-ment due to location in the Carpathian arc. The Wisłoka drainage basin of 3915 km² is largely underlain by less resistant, fine-grained flysch sandstones and shales. The narrow mountain zonę (up to 1000 m a.s.l.) and the wide foothill zonę (up to 560 m a.s.l.) are cut across by flat-floored valleys, up to 200—500 m deep (Starkel 1972). Because of smali height differences and location in the mountain shadow, annual precipitation is Iow and its annual pattern is little varied. Analysis of the seasonal distribution of the mean annual stream discharges reveals that the Wisłoka has a snowy regime, with dominant discharges in the winter half year (Punzet 1983).

In the upper Vistula drainage basin of 297 km² thick-bedded and coarse-grained sandstones and conglomerates predominate over shales. The resistant sandstones give rise to a coarse debris. The mountains (up to 1250 nt