Extended Data Fig. 10: Deposit volumes from field sampling and LiDAR.

a, Locations of fieldwork thickness measurements and deposition areas (blue). b, Deposit volumes from field measurements (x-axis) and LiDAR (primary y-axis) for all Meuse floodplains within the same areas, and relation to coverage of the LiDAR data per area (secondary y-axis). LiDAR-based overestimation can be explained by vegetation or gravel aggradation during the flood prior to sand deposition. LiDAR-based underestimation can be explained by a reduced coverage of LiDAR, i.e. in the large deposition areas of Ooijen-Wanssum and Negenoord (2 largest volumes). Analyses show that the field data are a solid base for the deposition volumes during the flood on the often-vegetated floodplains of the Meuse River where excavation works took place in 2021. LiDAR supplements the field work in areas with thick deposits (> 1 m) and outside survey areas. c, Floodplain level changes based on LiDAR data from April 2021 and August 2021. Brown (−1 – 0 m) generally represent small bed level lowering. The dark brown areas at the Eastern edge show overestimation of LiDAR where trees are (incorrectly) classified as ground in April 2021. d, Floodplain level changes based on the field surveys, plotted over the LiDAR differences in Panel c. Deposition patterns from LiDAR and fieldwork are identical, despite local differences in deposition depths and volumes. At the red arrow, LiDAR volumes exceed the fieldwork by 25%, probably due to detection of vegetation as ground in August 2021. The white arrow points to the area where LiDAR volumes are 33% lower than estimations from the field surveys, explainable by excavation works in the period April-July 2021, being part of the LiDAR-difference. The black arrow shows an example of underestimation of LiDAR volumes, because LiDAR measurements were missing in April 2021 for this area.