Dunes in the world’s big rivers are characterized by low-angle lee-side slopes and a complex shape

Julia Cisneros, Jim Best, Thaiënne van Dijk, Renato Paes de Almeida, Mario Amsler, Justin Boldt, Bernardo Freitas, Cristiano Galeazzi, Richard Huizinga, Marco Ianniruberto, Hongbo Ma, Jeffrey A. Nittrouer, Kevin Oberg, Oscar Orfeo, Dan Parsons, Ricardo Szupiany, Ping Wang, Yuanfeng Zhang

Research output: Contribution to journalArticlepeer-review

Abstract

Dunes form critical agents of bedload transport in all of the world’s big rivers, and constitute appreciable sources of bed roughness and flow resistance. Dunes also generate stratification that is the most common depositional feature of ancient riverine sediments. However, current models of dune dynamics and stratification are conditioned by bedform geometries observed in small rivers and laboratory experiments. For these dunes, the downstream lee-side is often assumed to be simple in shape and sloping at the angle of repose. Here we show, using a unique compilation of high-resolution bathymetry from a range of large rivers, that dunes are instead characterized predominantly by low-angle lee-side slopes (<10°), complex lee-side shapes with the steepest portion near the base of the lee-side slope and a height that is often only 10% of the local flow depth. This radically different shape of river dunes demands that such geometries are incorporated into predictions of flow resistance, water levels and flood risk and calls for rethinking of dune scaling relationships when reconstructing palaeoflow depths and a fundamental reappraisal of the character, and origin, of low-angle cross-stratification within interpretations of ancient alluvial sediments.

Original languageEnglish (US)
Pages (from-to)156-162
Number of pages7
JournalNature Geoscience
Volume13
Issue number2
DOIs
StatePublished - Jan 20 2020

ASJC Scopus subject areas

  • Earth and Planetary Sciences(all)

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