Backwater length estimates in modern and ancient fluvio-deltaic settings: Review and proposal of standardized workflows

A.e. Van yperen, J.m. Holbrook, M. Poyatos-Moré, I. Midtkandal

Research output: Contribution to journalArticleResearchpeer-review

Abstract

The backwater effect (i.e. adjustments in open-channel flow as a response to proximity of standing water) is used to predict down-dip changes in morphodynamics and consequent sediment distribution on fluvial systems. However, there is currently no standardized method to obtain input parameters to estimate backwater length, nor where to measure these variables, for both modern and ancient settings. This study reviews existing methods for estimating backwater lengths in both settings and proposes workflows to minimize ambiguity in the results.

The proposed workflows are prioritized based on practicality, accuracy, and smallest uncertainty ranges and allow different data types as input parameters. For the first time, applying multiple methods to obtain backwater length estimates is tested, both on a modern and ancient river system. In the modern case study, the riverbed intersection with sea level matches previously documented major changes in sedimentary trends. However, backwater lengths based on h/S (h = bankfull thalweg channel depth, S = slope) plot downstream of this zone which is characterized by major changes, when input parameters are derived from discharge and grain size. Therefore, we recommend obtaining bankfull thalweg channel depth from a cross-sectional profile if backwater length is estimated based on h/S. In the ancient case study, bankfull thalweg channel depth derived from fully preserved single-story channel fill and slope based on Shields' empirical relation with grain size, match changes in fluvial architectural style interpreted as a result of backwater effects.

This review is a critical step forward in discussing and acknowledging the uncertainties and ambiguity in obtaining the necessary input parameters to estimate and compare modern and stratigraphic backwater lengths. The proposed workflows facilitate comparability and applicability of future backwater length estimates and subsequent interpretations of the hydrodynamic environment and resulting stratigraphic record. Potential scaling relationships between the backwater length, sedimentary trends, and avulsion nodes make this of key importance as the latter two also play a crucial role in devastating floods when rivers change course.
Original languageEnglish
Article number104692
Number of pages24
JournalEarth-Science Reviews
Volume250
Early online date24 Jan 2024
DOIs
Publication statusPublished - Mar 2024

Keywords

  • Backwater effect
  • Backwater length
  • Fluvio-deltaic strata
  • Modern river systems
  • Source to sink

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