Karol Witkowski

Abstract Today, the development of river beds is shaped, not only by natural processes and phenomena, but also by anthropogenic impact. An acquaintanceship with the specifics of a bed system facilitates understanding of underlying mechanisms, allowing for both the protection of the natural environment and the management of flood risk. Work described here sought to determine the morphodynamics of the river bed along the regulated part of the Skawa (Fig. 1), i.e. in its lower, lowland reaches. Achievement of this aim was made possible by the identification of: morphogenetically uniform sections of the river, and factors intensifying sectional “rewilding” of its bed, with islands and central outwashes raking shape in consequence (Kamykowska et al., 2012). The typology referred to was based on the method for plotting a river bed after Kamykowska et al. (1999). Plotting proper was preceded by field observation, in line with which the Skawa bed was divided into 29 sections. The specified sections were then plotted by reference to a records book (Krzemień, 2012). Parameters obtained then provided for the typological analysis in fact identifying 12 morphogenetic sections of river bed (Fig. 2, line XII), as classified into 4 types differing in terms of the dominant process (Table 1). From among the 12 morphogenetic sections of river bed identified, the transport process dominates in 6 (river bed types A and B, Table 1). While it was mainly transport that characterised section 1 (assigned to type A); in section 5 transport and redeposition were observed (giving type B). The remaining 6 sections are in turn dominated by lateral erosion and redeposition (types C and D respectively), with these processes assuming high intensities in 2 (type D). The sections currently identified as transporting and eroding-redepositing do not present stable forms. Rather, the presence of unstable shore protections and construction of new ones (through bed regulation at Jaroszowice) combine with the upcoming start of operations of the dam at Świnna Poręba to force the bed to adjust constantly to new flow conditions. The operation of “Lake Mucharskie” (actually a reservoir) is in turn expected to increase vertical erosion. In the sections currently modelled by intense lateral erosion and redeposition (two multi-stream sections), morphological processes are expected to transform the river bed until it becomes a wide waterway area of the kind natural for that section of the valley, albeit currently narrowed to the river bed banks. The analysis of types of river bed along the lower Skawa points to the protected sections, dominated by transport, being the most susceptible to the rapid, significant transformations that may occur as a result of the destruction of rubble riprap.

Karol Witkowski

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