floodplain development reconstruction, anthropogenic impact, the Olše River, magnetic susceptibility, sedimentary record

Sedimentary records of the total six cores and two bank exposures were investigated in the Olše River floodplain. Set of laboratory analyses were supported by study of the old maps and archive river management and flood records. From the historical records it is obvious that even at the beginning of the 20th century the river in the study area had braiding pattern with 100 to 300 m wide gravel streambed. In 1930s the natural stream was replaced by straightened artificial channel and side channels were enclosed. After these modifications fine sediments were probably deposited on gravel bars of the former wide gravel streambed. Magnetic susceptibility (MS) measurements of upper fines of all investigated cores showed that these are very young because they were completely magnetically enhanced. Further sedimentary record interpretation was based on the assumption that MS peak determines the 1980s, time of the coal extraction, attached steel production and concentration of fly ashes culmination.