Using chemical composition and grain size distribution of a palaeochannel-fill to identify Lower Rhine flood events and their origin in the catchment

Abstract

At this moment no long-term records are available that reveal the upstream origin of sediment deposited during flood events in the Rhine. Tracing flood deposits in the lower Rhine back to Rhine subcatchments would increase the ability to trace sources of pollution, of flood events, and to reconstruct geomorphological developments throughout the catchment. In this research a data set of fluvial deposits throughout the Rhine catchment was created, covering both the Lower Rhine, the Oberrhein and three main tributaries (Neckar, Main and Moselle rivers). The data set was built up by corings from the lower Rhine and its upstream subcatchments and surface samples from locations throughout the subcatchments. Grain size analysis was performed on these samples to identify flood events. A XRF scan was performed to obtain the chemical composition of the samples. Chemical composition data was used to investigate the distribution and propagation of trace elements. Grain size data and chemical composition data were combined to find a correlation between specific set of elements and grain size fractions. Based on data analysis combined ith previous research, the Zr/Rb ratio was found to correlate with the sand fraction of the grain size data, and thus to act as a proxy for flood events. The Zr/Rb ratio was used to identify flood events in the chemical composition data, and to characterize the chemical composition of these flood events. The chemical composition of the corings and surface samples from the subcatchments were used to characterize the chemical composition of the subcatchments. Based on a combination of these characteristics an origin was suggested for some of the flood events. The 1671 and 1682 flood events are likely originate from the Oberrhein area. The 1726 and 1729 flood events are likely to originate from the Moselle area.