Substrate, sediment, and slope controls on bedrock channel geometry in postglacial streams

Whitbread, Katie; Jansen, John D.; Bishop, Paul; Attal, Mikaël

doi:10.1002/2014jf003295

Cited by 49 publications

(45 citation statements)

References 71 publications

(201 reference statements)

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“…An observation in many natural systems is that during the passage of a transient wave of incision, the river systems tends to narrow (Ouimet et al, ; Reusser et al, ; Valla et al, ). In many locations, the channel then widens following the passage of the transient signal or knickzone (Amos & Burbank, ; Finnegan et al, ; Kirby & Ouimet, ; Whitbread et al, ; Whittaker et al, ; Yanites et al, ). The modeling results presented here suggest that this behavior is a symptom of sediment transport dynamics playing a key role in controlling the channel morphology of these actively eroding river systems.…”

Section: Discussionmentioning

confidence: 99%

The Dynamics of Channel Slope, Width, and Sediment in Actively Eroding Bedrock River Systems

Yanites

2018

JGR Earth Surface

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The evolution of rivers in eroding landscapes plays a key role in determining landscape relief and modulating climate‐tectonic interactions. A common approach to quantifying river system evolution uses a one‐dimensional, detachment‐limited stream power equation. One potential drawback of this model is that it does not incorporate the effects of changes in channel width or the role of sediment transport dynamics. Here I present a new method for modeling the influence of channel width on river dynamics to explore how variable width and sediment transport impact river profile evolution. With this approach, vertical river erosion can operate based on any number of river erosion models, such as a simple shear stress model (e.g., detachment limited), sediment cover‐shear stress hybrid models, or mechanistic saltation‐abrasion models. I explore the sensitivity of these three models to increases in rock‐uplift rate (i.e., 2, 3, 5, 10, and 20× increase). Generally, the results show that incorporating channel width adjustment or sediment transport dynamics lowers the sensitivity of a river profile to rock‐uplift rate. For the sediment transport‐dependent models, the degree of sensitivity depends on whether the system is limited by bedrock exposure or erosion potential (i.e., detachment potential). The approach produces transient responses that reveal distinct patterns of width and slope, which may provide valuable insight into the limiting physical mechanisms of bedrock erosion in a region. The implications of the work are broad and include the potential to distinguish underlying erosion controls from field observations of width and slope as well as understanding climate‐tectonic interactions.

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Section: Discussionmentioning

confidence: 99%

The Dynamics of Channel Slope, Width, and Sediment in Actively Eroding Bedrock River Systems

Yanites

2018

JGR Earth Surface

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“…[], and Whitbread et al . []) Sediment has a D 16 , D 50 , and D 84 of 23, 70, and 146 mm, respectively (where D x is the grain size for which x % is finer; grain size distribution is shown in Figure c).…”

Section: Methodsmentioning

confidence: 99%

A Froude‐scaled model of a bedrock‐alluvial channel reach: 2. Sediment cover

Hodge

Hoey

2016

JGR Earth Surface

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Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. Abstract Previous research into sediment cover in bedrock-alluvial channels has focussed on total sediment cover, rather than the spatial distribution of cover within the channel. The latter is important because it determines the bedrock areas that are protected from erosion and the start and end of sediment transport pathways. We use a 1:10 Froude-scaled model of an 18 by 9 m reach of a bedrock-alluvial channel to study the production and erosion of sediment patches and hence the spatial relationships between flow, bed topography, and sediment dynamics. The hydraulic data from this bed are presented in the companion paper. In these experiments specified volumes of sediment were supplied at the upstream edge of the model reach as single inputs, at each of a range of discharges. This sediment formed patches, and once these stabilized, flow was steadily increased to erode the patches. In summary: (1) patches tend to initiate in the lowest areas of the bed, but areas of topographically induced high flow velocity can inhibit patch development; (2) at low sediment inputs the extent of sediment patches is determined by the bed topography and can be insensitive to the exact volume of sediment supplied; and (3) at higher sediment inputs more extensive patches are produced, stabilized by grain-grain and grain-flow interactions and less influenced by the bed topography. Bedrock topography can therefore be an important constraint on sediment patch dynamics, and topographic metrics are required that incorporate its within-reach variability. The magnitude and timing of sediment input events controls reach-scale sediment cover.

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“…Although most models of bedrock channel incision presume that channel width ( W ) follows a power law scaling with discharge ( Q ) or drainage area ( A , a proxy for Q ), similar to that observed in alluvial channels ( W ∝ Q 0.5 ) [ Hack , ; Wohl and David , ], field studies of natural channels present conflicting observations. Measurements of channel width in some fluvial systems with both alluvial and bedrock reaches exhibit similar scaling [ Montgomery and Gran , ; Whipple , ; Whitbread et al ., ], even in regions with strongly varying rock uplift rate [ Snyder et al ., ], suggesting that channel width is governed by a similar set of processes in both mobile and fixed substrates. In contrast, several recent field studies document systematic variations in channel width in channels adjusted to varying rates of base‐level fall or rock uplift [ Duvall et al ., ; Finnegan et al ., ; Amos and Burbank , ; Yanites et al ., 2010; Kirby and Ouimet , ].…”

Section: Introductionmentioning

confidence: 98%

Characterizing the transient geomorphic response to base‐level fall in the northeastern Tibetan Plateau

et al. 2017

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Analysis of hillslope gradient, landscape relief, and channel steepness in the Daxia River basin provides evidence of a transient geomorphic response to base‐level fall on the northeastern Tibetan Plateau. Low‐gradient channels and gentle hillslopes of the upper watershed are separated from a steeper, high‐relief landscape by a series of convex knickzones along channel longitudinal profiles. Downstream projection of the “relict” portions of the profiles implies ~800–850 m of incision, consistent with geologic and geomorphic records of post ~1.7 Ma incision in the lower watershed. We combine optically stimulated luminescence dating of fluvial terrace deposits to constrain incision rates downstream of knickpoints with catchment‐averaged 10Be concentrations in modern sediment to estimate erosion rates in tributary basins both above and below knickpoints. Both sources of data imply landscape lowering rates of ~300 m Ma−1 below the knickpoint and ~50–100 m Ma−1 above. Field measurements of channel width (n = 48) and calculations of bankfull discharge (n = 9) allow determination of scaling relations among channel hydraulic geometry, discharge, and contributing area that we employ to estimate the patterns of basal shear stress, unit stream power, and bed load transport rate throughout the channel network. Our results imply a clear downstream increase of incision potential; this result would appear to be consistent with a detachment‐limited response to imposed base‐level fall, in which steepening of channels drives an increase in erosion rates. In contrast, however, we do not observe apparent narrowing of channels across the transition from slowly eroding to rapidly eroding portions of the watershed. Rather, the present‐day channel morphology as well as its scaling of hydraulic geometry imply that the river is primarily adjusted to transport its sediment load and suggest that channel morphology may not always reflect the presence of knickpoints and differences in landscape relief.

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Substrate, sediment, and slope controls on bedrock channel geometry in postglacial streams

Cited by 49 publications

References 71 publications

The Dynamics of Channel Slope, Width, and Sediment in Actively Eroding Bedrock River Systems

The Dynamics of Channel Slope, Width, and Sediment in Actively Eroding Bedrock River Systems

A Froude‐scaled model of a bedrock‐alluvial channel reach: 2. Sediment cover

Characterizing the transient geomorphic response to base‐level fall in the northeastern Tibetan Plateau

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