Late Holocene flood magnitudes in the Lower Rhine river valley and upper delta resolved by a two‐dimensional hydraulic modelling approach

Bas van der Meulen*, Anouk Bomers, Kim M. Cohen, Hans Middelkoop

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

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Abstract

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 × 103 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 m3/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.
Original languageEnglish
Pages (from-to)853-868
Number of pages16
JournalEarth surface processes and landforms
Volume46
Issue number4
Early online date11 Jan 2021
DOIs
Publication statusPublished - 30 Mar 2021

Keywords

  • UT-Hybrid-D
  • Lower Rhine
  • Millennial flood
  • Palaeohydrology
  • Rhine delta
  • Hydraulic model
  • hydraulic model
  • millennial flood
  • palaeohydrology

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