Lower Rhine historical flood magnitudes of the last 450years reproduced from grain-size measurements of flood deposits using End Member Modelling

Objective
The objective of this research was to unlock the potential of fluvial archives to create flood chronologies, based on grain-size characteristics of flood deposits located in two recently formed fluvio-lacustrine sequences.

Methods
Grain-size data was compared with contemporaneous discharge measurements (for the Lower Rhine, The Netherlands). Regression relations between coarse-tail grain-size parameters and measured discharge were established for the last ~ 240 years, and applied to the older parts of both cores – resulting in peak discharge estimates back to AD ~ 1550.

Results
Grain-size descriptive parameters such as the 95th percentile and end-member modelling outcomes correlate well with discharge and turn out to be sensitive proxies for inferring flood magnitudes. Locally, geomorphological changes influence the relation between peak discharge magnitudes and flood bed coarseness, but these can be assessed, using continuous flood layer and background sedimentation measurements to standardize grain-size descriptive parameters.

Conclusion/implications
Flood records distilled from sedimentary archives hold great potential for extending existing records of observed discharge and aid establishment of design discharge for flood protection measures and assessment of non-stationarity of the flooding regime due to climatic and anthropogenic forcing.