OVERBANK SEDIMENTS ALONG THE MIDDLE WIEPRZA AS A RECORD OF FLOOD PHENOMENA JACEK KACZMARZYK, WACLAW FLOREK Department of Geomorphology and Quaternary Geology, Institute of Geograpghy and Regional Studies, Pomeranian University in Słupsk, Partyzantów 27, 76-200 Słupsk, Poland E-mails: kaczmarz@go2.pl; florekw@apsl.edu.pl Abstract: Today’s flood events along the River Wieprza assume a quite characteristic course entail- ing calm spillovers of water from the bed in places of riverbank lowering and in sections above and below bridges, where a narrowing of the channel is present. The identity of the land inundated relates to morphology, the near-channel part of a floodplain may be affected or those parts in depressions that serve as flood basins. Riverbank exposures on both sides of the present river channel plus pits reveal the construction of the Wieprza floodplain. The sediments that build the floodplain represent channel and overbank facies with subfacies of palaeomeander fills. Analysed exposures are located along the valley section be- tween Sławsko and Staniewice, mostly in close proximity to the Early Mediaeval fortified site of WrzeĞnica. The content of the exposures indicates that the uniform cover of overbank sediments across the floodplain emerged during the last 1000 years. It is now impossible to say when exactly, so it is unknown what the rank of the extreme floods which took place at the end of 19 th century was, and what their role in forming the present floodplain. Key words: paleomeanders, Holocene, overbank deposits, flood, floodplain, Medieval fortified site, Wieprza river. INTRODUCTION The range of occurrence and lithologi- cal characteristics of overbank sediments are viewed as important indicators of the functioning of a river system, reflecting hydrological and physiographic character- istics, and the degree and nature of human interference in the catchment and channel environments. Recently observed extreme meteorological and hydrological events, commonly linked with global warming, cause high water to appear more frequently than in previous decades, this spilling over the banks of rivers flowing through the re- gion of Pomerania. The above explains the authors’ interest in characteristics of con- temporary overbank sediments, as well as the attempt made to compare them with sed- iments accumulated during the last millen- nium. In the opinion of the authors this pro- vides for an assessment of the importance of contemporary hydrological phenomena, as set against changes taking place in the younger part of the Sub-Atlantic period. The first phase to the investigations pre- sented below was financed from the own funds of the Pomeranian Pedagogical Acad- emy in Słupsk, while later financing has been from Grant PBZ-KBN-086/P04/2003 GEOGRAPHIA POLONICA 2010, 83, 1, 13–24 http://rcin.org.pl