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Late Holocene flood magnitudes in the Lower Rhine river valley and upper delta resolved by a two‐dimensional hydraulic modelling approach
Author(s) -
Meulen Bas,
Bomers Anouk,
Cohen Kim M.,
Middelkoop Hans
Publication year - 2021
Publication title -
earth surface processes and landforms
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.294
H-Index - 127
eISSN - 1096-9837
pISSN - 0197-9337
DOI - 10.1002/esp.5071
Subject(s) - flood myth , floodplain , holocene , geology , fluvial , hydrology (agriculture) , alluvium , magnitude (astronomy) , terrain , delta , physical geography , geomorphology , archaeology , paleontology , geotechnical engineering , geography , physics , cartography , structural basin , astronomy , aerospace engineering , engineering
Palaeoflood hydraulic modelling is essential for quantifying ‘millennial flood’ events not covered in the instrumental record. Palaeoflood modelling research has largely focused on one‐dimensional analysis for geomorphologically stable fluvial settings because two‐dimensional analysis for dynamic alluvial settings is time consuming and requires a detailed representation of the past landscape. In this study, we make the step to spatially continuous palaeoflood modelling for a large and dynamic lowland area. We applied advanced hydraulic model simulations (1D–2D coupled set‐up in HEC‐RAS with 950 channel sections and 108 × 10 3 floodplain grid cells) to quantify the extent and magnitude of past floods in the Lower Rhine river valley and upper delta. As input, we used a high‐resolution terrain reconstruction (palaeo‐DEM) of the area in early mediaeval times, complemented with hydraulic roughness values. After conducting a series of model runs with increasing discharge magnitudes at the upstream boundary, we compared the simulated flood water levels with an inventory of exceeded and non‐exceeded elevations extracted from various geological, archaeological and historical sources. This comparison demonstrated a Lower Rhine millennial flood magnitude of approximately 14,000 m 3 /s for the Late Holocene period before late mediaeval times. This value exceeds the largest measured discharges in the instrumental record, but not the design discharges currently accounted for in flood risk management.