Dynamic bedrock channel width during knickpoint retreat enhances undercutting of coupled hillslopes

Baynes, Edwin; Lague, Dimitri; Steer, Philippe; Davy, Philippe

doi:10.1002/esp.5477

Cited by 10 publications

(20 citation statements)

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“…According to a numerical study that considered the effects of sediment cover, channel narrowing occurs after the knickpoint passage, but as the knickpoint travels upstream the local sediment supply continues to increase, resulting in gradual widening of the channel (Yanites, 2018). A similar width adjustment was observed in a flume experiment (Baynes et al, 2022). Hillslope morphology is set by river incision at its base.…”

Section: Introductionmentioning

confidence: 75%

Transient Response and Adjustment Timescales of Channel Width and Angle of Valley-Side Slopes to Accelerated Incision

Takahashi

Ôta

Toda

et al. 2022

Preprint

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Studying bedrock rivers during their transient states helps understand the response of a fluvial system to changed boundary conditions. Although studies show how river form adjusts to changes in incision or rock uplift rates, field constraints on the timescale of this adjustment are limited. We present a method that uses knickpoint travel time to estimate the adjustment times of channel width and angle of valley-side slopes to accelerated incision. The travel time of knickpoints between their current positions and the points where changes in width or hillslope angle have just finished represents the time required for morphological adjustment after knickpoint passage. We documented channel slopes, channel widths, and hillslope angles along six rivers that cross an active normal fault in Iwaki, Japan, and identified river sections in a transient state. Channel slopes and basin-averaged erosion rates determined from 10 Be concentrations are distinct between rivers near and distant from the fault, suggesting that past increases in fault throw rates triggered the knickpoint formation and the observed transient response.Adjustment time depends on the slope exponent in the detachment-limited model and is 2-5 times greater for channel width than hillslope angle, indicating that catchment adjustment times can be much longer than times predicted only by knickpoint travel time. The fact that channel slope, channel width, and hillslope angle have distinct adjustment times underlines the importance of correctly identifying river sections that are fully adjusted to the new boundary conditions when inferring erosion or relative uplift rates for bedrock rivers.

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Section: Introductionmentioning

confidence: 75%

Transient Response and Adjustment Timescales of Channel Width and Angle of Valley-Side Slopes to Accelerated Incision

Takahashi

Ôta

Toda

et al. 2022

Preprint

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“…The elevation of the valley floor in the trunk channel, due to overdeepening by ice, acts as a base level that the tributaries are adjusting to (Valla et al., 2010), and the zones of high K Sn are the knickpoints that separate the downstream reaches that adjusted to the new base level from upstream reaches that are typically low relief with low slopes (e.g., Figure 3b). We therefore hypothesize that the extent of postglacial fluvial adjustment (i.e., headward knickpoint retreat and corresponding channel and hillslope adjustment; Baynes et al., 2022) is an important control on the morphological impact of extreme events. As demonstrated here, the zone of potential sediment mobilization is much larger and located higher up in the catchment in Slei Gill compared to Grinton Beck where sediment mobilization is focused in the downstream reach only.…”

Section: Discussionmentioning

confidence: 99%

Extreme Flood Sediment Production and Export Controlled by Reach‐Scale Morphology

Baynes

Kincey

Warburton

2023

Geophysical Research Letters

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Rapid earth surface evolution is discrete in nature, with long periods of quiescence punctuated by relatively short-duration events when the majority of geomorphic work takes place (Baynes et al., 2015;Jones et al., 2021). In extreme cases, infrequent high-magnitude events can leave a long-lasting legacy on the landscape and dominate long-term evolution by contributing to widespread erosion, sediment production, transport and deposition within catchments (Benda & Dunne, 1997;Duller et al., 2014). Such events are typically characterized by very high river runoff, large volumes of sediment production and transport, leading to rapid landscape change and potentially hazardous conditions for local communities (Cook et al., 2018). Following rare extreme events, landscapes enter a period of recovery during which they gradually return to background conditions and sediment export rates (Brunsden & Thornes, 1979;Hovius et al., 2011;Marc et al., 2015). The balance between the recovery timescale and the magnitude and frequency of extreme events determines whether a landscape is in a transient state (e.g., continually eroding or aggrading) over the long-term (Allen, 2008;Duller et al., 2014). Despite this, our understanding of the fundamental mechanisms that control the impact of extreme events on landscapes remains limited, as it is based on observations of the local morphological impact of extreme events that typically occur within single catchments (e.g., Licciardello et al., 2019;Milan, 2012;Scorpio et al., 2022). Therefore, it is difficult to develop a broadly-applicable predictive tool that can establish the expected future impact of extreme events in diverse catchments. Over-reliance on identifying the impacts of extreme events from single catchments means subtle controls of catchment morphology could be overlooked. With the frequency and magnitude of rainfall-induced extreme events expected to increase in the future as a result of climate changes (Madsen et al., 2014), it is therefore critical to increase the quantitative understanding of the key controls that govern the impact of extreme events on landscapes.

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“…In this study, channel width kept narrower after the passage of the knickpoints (Figures 4c and 4f). Baynes et al (2022) reported that the channel first narrowed and then became wider following the knickpoint passage. This shift from narrowing to widening corresponded with a transition from bed degradation to aggradation.…”

Section: Implications For Transient Responsementioning

confidence: 99%

“…Baynes et al. (2022) conducted flume experiments and reported width evolution during knickpoint retreat. They found that width decreased upstream of the knickpoint and reached the minimum at the knickpoint, and then increased after the passage of the knickpoint.…”

Section: Introductionmentioning

confidence: 99%

“…According to a numerical study that considered the effects of sediment cover, channel narrowing occurs after the knickpoint passage, but as the knickpoint travels upstream, the local sediment supply continues to increase, resulting in gradual widening of the channel (Yanites, 2018). Baynes et al (2022) conducted flume experiments and reported width evolution during knickpoint retreat. They found that width decreased upstream of the knickpoint and reached the minimum at the knickpoint, and then increased after the passage of the knickpoint.…”

mentioning

confidence: 99%

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Transient Response and Adjustment Timescales of Channel Width and Angle of Valley‐Side Slopes to Accelerated Incision

et al. 2023

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Studying bedrock rivers during their transient states helps understand the response of a fluvial system to the changing boundary conditions. Although theoretical studies predict how river form adjusts to changes in incision or rock uplift rates, field constraints on the timescale of this adjustment are limited. We investigated the transient behavior of channels and hillslopes and estimated the adjustment times of channel width and angle of valley‐side slopes to accelerated incision based on knickpoint travel time. We documented channel slopes, channel widths, and hillslope angles along six rivers around an active normal fault in Iwaki, Japan, and identified river sections in a transient state. Channel slopes and basin‐averaged erosion rates determined from 10Be concentrations are distinct between rivers near and distant from the fault, suggesting that past increases in fault throw rates triggered the knickpoint formation and the observed transient response. Adjustment time for width is at least 105 years and can take 106 years after the knickpoint passage. Adjustment time for hillslope angles is generally shorter than for channel width. However, the hillslope adjustment may take longer than previously reported if the effect of width adjustment on hillslope angles is significant or the complete adjustment of hillslope angles is considered. The fact that channel slope, channel width, and hillslope angle have distinct adjustment times underlines the importance of correctly identifying river sections that are fully adjusted to the new boundary conditions when inferring erosion or relative uplift rates for bedrock rivers.

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Dynamic bedrock channel width during knickpoint retreat enhances undercutting of coupled hillslopes

Abstract: Dynamic bedrock channel width during knickpoint retreat enhances undercutting of coupled hillslopes

Cited by 10 publications

References 57 publications

Transient Response and Adjustment Timescales of Channel Width and Angle of Valley-Side Slopes to Accelerated Incision

Transient Response and Adjustment Timescales of Channel Width and Angle of Valley-Side Slopes to Accelerated Incision

Extreme Flood Sediment Production and Export Controlled by Reach‐Scale Morphology

Transient Response and Adjustment Timescales of Channel Width and Angle of Valley‐Side Slopes to Accelerated Incision

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