Holocene floodplain sediment storage and hillslope erosion within the Rhine catchment

The response of fluvial systems to land use and climate change varies depending on catchment size. While forcing-response mechanisms of small catchments are reasonably well understood, the response of larger drainage basins is less clear. In particular, the impact of land use and climate change on the Rhine system is poorly understood because of the catchment size (185 000 km²) and the long history of human cultivation, which started approximately 7500 years ago. A sediment budget is calculated to specify the amount of alluvial sediment that was deposited during the Holocene and to estimate long-term soil erosion rates. The results suggest that 59±14 X 10⁹ t of Holocene alluvial sediment is stored in the non-alpine part of the Rhine catchment (South and Central Germany, Eastern France, The Netherlands). About 50% of Holocene alluvial sediment is deposited along the trunk valley and the delta (Upper Rhine, Lower Rhine, coastal plain), while the rest is stored along the tributary valleys. The floodplain sediment storage corresponds to a mean erosion rate of 0.55±0.16 t/ha per yr (38.5±10.7 mm/kyr) across the Rhine catchment outside the Alps. This Holocene-averaged estimate amounts for sediments that were delivered to the channel network and is at the lower limit of erosion rates from other studies of different methodology.