Quantification of alluvial sediment storage in contrasting environments: Methodology and error estimation

Floodplains are an important sediment sink in many temperate catchments during the Holocene, especially where anthropogenic land use had a dominant influence on the landscape. As such, the quantification of Holocene floodplain deposits plays an important role in the global interest in continent-ocean transfers of sediments. In this study the total Holocene floodplain deposition was quantified for three contrasting catchments in Belgium, characterized by a different fluvial architecture and Holocene deposits thickness. Several methods were used to delineate the floodplain, and combined with different amounts of field data in Monte Carlo type simulations. The results show that the method used to delineate the floodplains is responsible for the largest uncertainties on the results, while the number of used field data has less influence. on the results of this study, ca one cross-section each 30 km valley length, combined with at least 5 corings per cross-section, should yield a reliable quantification of catchment wide floodplain deposition. sults show that inter- and intra-catchment variability in floodplain deposition varies largely between the studied catchments. Based on the available data, spatial patterns of floodplain sediment storage can be explained by a combination of sediment delivery to the fluvial system and the sediment transport capacity of the fluvial system, which depends on floodplain slope and runoff discharge peaks.