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Abstract River bedforms and their deposits—fluvial cross strata— respond to floods. However, it is unclear if all floods are equally represented in cross strata. Here, using a series of physical experiments in which bedforms were subjected to equivalent flood magnitudes over varying durations, we demonstrate the existence of a lower bound on flood durations that are represented in cross strata. We show that the scour depths and preserved set thickness are indistinguishable from baseflow conditions when the rising‐limb duration of floods is shorter than the baseflow‐equilibrated bedform turnover timescale—time required to displace the volume of a single bedform at baseflow conditions. In contrast, scour depth and preserved set thickness distributions deviate from baseflow conditions when flood rising‐limb duration exceeds the baseflow‐equilibrated bedform turnover timescale, causing preferential preservation of falling‐limb bedform dynamics. Our work provides a previously unrecognized quantitative bound on flood durations that are represented in fluvial cross strata.
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The Role of Fluvial Morphodynamic Hierarchy in Shaping Bedform Deposits
Abstract Fluvial cross strata are fundamental sedimentary structures that record past flow and sediment transport conditions. Bedform preservation can be significantly influenced by the presence of larger‐scale topographic features that cause spatial gradients in flow. However, our understanding of the controls on cross strata preservation in the presence of a morphodynamic hierarchy is limited. Here, using high‐resolution bathymetry from a physical experiment, we quantify bedform evolution and cross strata preservation in a zone of flow expansion and deceleration. Results show that the size and celerity of superimposed bedforms decreases along the host‐bedform lee slope, leading to a systematic downstream increase in the sediment accumulation rate relative to bedform celerity. This increase in local bedform climb angle results in the preservation of a larger fraction of formative bedforms. Our results highlight the need to revise current paleohydraulic reconstruction models, and demonstrates that fluvial morphodynamic hierarchy is a fundamental determinant of sedimentary strata.
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- Award ID(s):
- 1935669
- PAR ID:
- 10549264
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 51
- Issue:
- 20
- ISSN:
- 0094-8276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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