10.2478/v10060-008-0068-4 Annals of Warsaw University of Life Sciences – SGGW Land Reclamation No 42 (1), 2010: 93–104 (Ann. Warsaw Univ. of Life Sci. – SGGW, Land Reclam. 42 (1), 2010) Basement of the alluvia infl uence on the channel pattern in example of selected reach of the Pilica River TOMASZ FALKOWSKI Department of Geotechnical Engineering, Warsaw University of Life Sciences – SGGW Abstract: Basement of the alluvia infl uence on the sing and wandering rivers (Miall 1996; channel pattern in example of selected reach of the Zieliński 1998). In the Polish Lowlands Pilica River. The type of the channel pattern is be- the most common types are meandering ing considered as indicative element of the fl uvial environment, especially for lowland, mature riv- and braided rivers. Multi-channel river ers. Investigations carried out in the Pilica River reaches defi ned as anastomosing rivers valley (example of such river) between Inowłódz (Gradziński et al. 2003) occur in Poland and Domaniewice (grant no 2P04E 069 29, Mini- in polygenic valley reaches, which often stry of Science) have shown that morphological represent adapted melt-out basins after features of the valley bottom (channel zone, as well as fl ood terrace) depends not only on river overfl ow lakes (Falkowski 1975). The regime, but also on channel zone geological set- presence of straight rivers is almost ting. Elements of the Pilica valley geology infl u- always linked with the character of the encing on fl uvial processes are protrusions of al- channel basement (Twindale 2004). Such luvia basement composed of deposits resistant to rivers occur within the outcrops of rocks erosion, crop out in the channel zone. resistant to erosion, which form linear Key words: channel pattern, alluvia basement, tectonic structures. In the Polish Low- erosion resistant deposits. land, short reaches of such rivers can be encountered near escarpments of moraine plateaus eroded by the rivers. INTRODUCTION In the history of river valleys in the The type of channel pattern is the most Polish Lowlands, climate was the main signifi cant index of the hydrological factor infl uencing the specifi c hydro- regime of a river (Allen 1970). The logical river regime and thus the type changing relations between particular of channel. Climatic changes that took elements of the hydrological regime such place in the terminal Pleistocene and the as discharge, water state, fl ow velocity, Holocene resulted in the creation of river water temperature, ice cover and sediment terraces during the evolution of present- transport (Dynowska 1971) infl uence the -day rivers. During the Last Glaciation, balance between erosional and accumula- for a relatively short time the Scandina- tion processes. Generally, fi ve main types vian ice-sheet twice (Mojski 2005) cove- of channel development are distinguished: red northern and western Poland. In the straight, meandering, braided, anastomo- ice-free area the hydrological regime of 94 T. Falkowski the rivers was infl uenced by permafrost -day terrace (Falkowski 1975, 1990; Star- (Jahn 1970) and lack of dense vegetation kel 1983). Changes in the river regime cover. At low retention of the catchment are refl ected in traces of channel migra- basin, surface runoff played a signifi cant tion that may be observed in particular role in the water balance. It supplied accumulation horizons (terraces) of river considerable amounts of sediment from valleys in the Polish Lowlands. They are the slopes to the channels. Thus, braided particularly well-recognizable on aerial rivers overloaded with sediment func- (Falkowski 1975; Szumański 1986) and tioned in the Polish Lowlands (Zieliński satellite photographs. A thorough charac- 1993; Mojski 2005). They often fi lled teristic of the infl uence of human activity the rock-cut benches of the present-day on the volume of sediment transported valleys that developed in the Eemian by rivers in the world was presented by Interglacial, forming surfaces of the Walling (2006). upper terraces. The Pleistocene/Holo- According to Wolman, Miller (1960), cene warming resulted in dense vegeta- Leopold et al. (1964), and Dury (1980), tion within the drainage basin. Increase the character of channel processes is more of surface retention caused leveling of signifi cantly infl uenced by long-term, fl ow with time and evolution of the river medium-scale phenomena and not extre- systems towards meandering rivers. The me incidents. However, during fl ood-water rivers incised into the surface of Pleis- some rivers may signifi cantly transform tocene upper terraces forming fl ood ter- the valley fl oor; as a result these trans- races (Falkowski 1975; Kozarski, Rot- formations considerably infl uence fl uvial nicki 1977; Mycielska-Dowgiałło 1978; processes that take place during long-term Wiśniewski 1987; Florek 1991; Blum medium- and low-water states. The sig- and Tornqvist 2000; Leigh et al. 2004). nifi cance of high-water states in the mor- About 6000 years BP, the hydrological phology of present-day river valleys in the regime of rivers in the Polish Lowlands Polish Lowlands is marked by the forma- began to be infl uenced by human activity, tion of the present-day terrace due to the when forest fi res and clearance were applied activity of fl ood-water. Its surface usually to gain arable ground. Such activities lies above other parts of the fl ood terrace. caused a subsequent change in the hydro- Accumulation of fi ne-grained sediments logical regime of the rivers, manifested of the fl ood facies deposited from sus- by increased surface runoff and sediment pension is much slower than aggradation supply (Falkowski 1975; Mycielska- in the near-channel zone, where coarser -Dowgiałło 1978; Starkel 1983). The material is deposited through decantation present-day rivers of the Polish Lowlands, from fl ood-water. characterized by uneven fl ow (Starkel The depth of the channel of present- 1994) typically have braided channels, -day rivers increases during fl ooding. and the process of their transformation After the fl ood wave moves downriver, under human infl uence is referred to run- the channel is fi lled with the transported ning wild (Falkowski 1975). The fl ood sediment as the transporting force of the plain adjacent to the channel formed in river decreases. In the Middle Vistula such processes is known as the present- River channel, such changes of the eleva- Basement of the alluvia infl uence on the channel pattern... 95 tion of the channel fl oor between high- constructions and fl ood embankments and medium-water may exceed 10 m (Falkowski 2007a, b). (Falkowski 2006). During fl ooding, the A trend to increase differences basement of the present-day alluvia may between extreme fl ows is presently evi- be exposed, particularly in places where dent in the hydrological regime of rivers its top lies at relatively shallow depths. in the Polish Lowlands (Ozga-Zielińska In such places the alluvial basement is 1997). The infl uence of the alluvial base- built of soils more resistant to erosion. ment on the course of channel processes, The morphology of their top surface may which during meander formation was therefore infl uence the pattern of the ri- rather low (due to balanced fl ow), is ver’s main course, and thus the processes much more signifi cant presently due to of erosion and accumulation within the increased depth of fl ood-water activity. channel and the fl ood-plain (Falkowski Features of channel morphology that are 2007a, b). Twindale (2004) pointed out indexes of a particular river regime and the relation of the river valley basement indicate the specifi c dynamics of ero- on the course of present-day channel sional and accumulation processes, are processes. increasingly dependent on the geological In regulated reaches the infl uence of setting of the channel zone, particularly the alluvial basement is often more sig- in reaches where the fl ood-water channel nifi cant than in the natural reaches. Nar- width is restricted by fl ood embankments. rowing of the fl ood-water channel by fl ood embankments increases the depth AIM AND METHODS OF STUDIES of fl ood-water erosion. In such places the infl uence of morphology of the resistant The studies carried out in the Pilica River basement on the river course concentra- valley between Inowłódz and Domanie- tion results often in damage of regulation wice (Fig. 1) were focused on determi- FIGURE 1. Location of study area 96 T. Falkowski ning the relation of the channel zone as fl ood-terrace and the channels of the well as fl oodplain morphology (contem- studied rivers were also analyzed. Soil porary and Holocene channels pattern) analysis as well as sedimentological and with the morphology and lithology of the pollen analysis of the alluvial sediments alluvial basement. The channel pattern is were conducted. The studies were made connected with a specifi c variability of in the frame of project no 2P04E 069 29 alluvial soil properties (Myślińska 1984; Signifi cance of morphogenetic factors in Kraużlis et al. 2003). Morphogenetic the development of habitat variability in units corresponding to particular stages selected reaches of river valleys in the of the fl uvial setting evolution (refl ected Polish Lowlands, fi nanced by the Mini- in the channel pattern) are often the basis stry of Science and Higher Education of of units applied in documenting the geo- Poland. logical-engineering conditions of river valleys (Falkowski 1990; Gilvear 1999). RESULTS The studied reach of the Pilica River valley incises into a fragment of a plateau The analyzed fragment of the Pilica with a mature, denudation morphology, valley is developed in Middle Jurassic developed since the end of the Middle siliceous sandstones and in various Pleis- Polish Glaciations. The rock-cut bench tocene deposits (Figs 2, 3).