Impact of channel regulation on sedimentation on the Lower Dunajec floodplains

In the last century the Dunajec channel in its lower river course was considerably transformed due to channelization works. The former multi-thread river channel was replaced by a single one, resulting in abandonment of side channels. Groynes were constructed on both main and side channel. Quick filling up of the inter-groyne basins reduced channel width and capacity. In the study area, a side channel with groynes was abandoned and filled up. The aim of this study was to reconstruct the rate and depositional conditions of the sediments infilling the abandoned channel. These sediments are 215-222 cm thick and were deposited at an average rate of 5-5.2 cm/year. Their sedimentary environment was inferred based on a C/M diagram. The depositional conditions in the abandoned channel were determined by two major factors: distance to the active channel and difference in elevation between depositional surface and active channel. Close to the active channel, 61% of sediment was deposited from suspension and 39% by traction current. At a distance of 200 m to the active channel, 100% of sediment was deposited from suspension, with 25% falling from pelagic suspension. At an early stage of infilling of abandoned channel, the depositional flows are more energetic and the deposition rate is higher than in the later stage. The investigated sediments are an example of accumulation induced by channelization works. The spatial distribution of these fine-grained, quickly deposited sediments is determined by the course of the abandoned channel.