Floodplain sedimentation rates, soil properties and recent flood history in southern Québec

This study examines the depositional and pedogenic processes observed in reaches affected by periodic flooding in river basins of southern Québec and presents a reconstruction of flood events in this area from 1865 to 2005. This record shows a significant increase in flooding over the last 100 years, and successive overbank flood deposits show evidence for a recent increase in flood frequency in this region. The frequency of flooding leads to fine sediments being regularly deposited on floodplains producing weakly developed alluvial soils. Sedimentological and pedological analyses combined with radiocarbon and 210Pb dating has allowed the determination of floodplain sedimentation rates. The radiocarbon data obtained from organic layers buried in floodplain soils show variable ages over the last 2210 radiocarbon years. Sedimentation rates obtained from radiocarbon dating and both CRS and CF:CS models for 210Pb show average values ranging from 1.0 to 7.6 mm yr− 1, 2.1 to 10.7 mm yr− 1 and 2.6 to 6.0 mm yr− 1 respectively. This variability can be explained by the models used and depends to a large extent on the geomorphological context and local fluvial dynamics specific to each study area.