Waterfall height sets the mechanism and rate of upstream retreat

Inoue, Takuya; Izumi, Norihiro; Scheingross, Joel S.; Hiramatsu, Yoshio; Tanigawa, Shunsuke; Sumner, Tamaki

doi:10.1130/g51039.1

Cited by 6 publications

(2 citation statements)

References 39 publications

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“…Meanwhile, Dinkey Creek waterfalls have larger drop heights (mean height of 3.3 m, Figure 9f), which may contribute to greater correlation between waterfall frequency and slope. This is in line with recent experimental results (Inoue et al, 2023) showing that shorter waterfalls have faster upstream retreat rates than taller waterfalls.…”

Section: Longitudinal Profiles and Waterfall Frequencysupporting

confidence: 93%

“…This idea is grounded in cyclic step theory, in which Froude supercritical flow causes periodic, upstream migrating steps (often termed cyclic steps) to develop in both alluvial (Parker & Izumi, 2000) and bedrock (Izumi et al., 2017) channels. Experiments show that cyclic steps can develop into waterfalls with a freefalling water jet cascading over a drop height up to 3–6 times the flow depth (Inoue et al., 2023; Scheingross et al., 2019). This is supported by an analysis of 360 waterfalls in the San Gabriel Mountains, California showing that waterfalls with characteristic scaling of drop height and spacing (indicating likely formation via growth of cyclic steps) formed only above a threshold slope of ∼3%–7% (Groh & Scheingross, 2022), coincident with the onset of Froude supercritical flow (Palucis & Lamb, 2017).…”

Section: Model Developmentmentioning

confidence: 99%

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Impacts of Spontaneous Waterfall Development on Bedrock River Longitudinal Profile Morphology

Rothman,

Scheingross,

McCoy

et al. 2023

JGR Earth Surface

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River profiles are shaped by climatic and tectonic history, lithology, and internal feedbacks between flow hydraulics, sediment transport and erosion. In steep channels, waterfalls may self‐form without changes in external forcing (i.e., autogenic formation) and erode at rates faster or slower than an equivalent channel without waterfalls. We use a 1‐D numerical model to investigate how self‐formed waterfalls alter the morphology of bedrock river longitudinal profiles. We modify the standard stream power model to include a slope threshold above which waterfalls spontaneously form and a rate constant allowing waterfalls to erode faster or slower than other fluvial processes. Using this model, we explore how waterfall formation alters both steady state and transient longitudinal profile forms. Our model predicts that fast waterfalls create km‐scale reaches in a dynamic equilibrium with channel slope held approximately constant at the threshold slope for waterfall formation, while slow waterfalls can create local channel slope maxima at the location of slow waterfall development. Furthermore, slow waterfall profiles integrate past base level histories, leading to multiple possible profile forms, even at steady‐state. Consistency between our model predictions and field observations of waterfall‐rich rivers in the Kings and Kaweah drainages in the southern Sierra Nevada, California, supports the hypothesis that waterfall formation can modulate river profiles in nature. Our findings may help identify how bedrock channels are influenced by waterfall erosion and aid in distinguishing between signatures of external and internal perturbations, thereby strengthening our ability to interpret past climate and tectonic changes from river longitudinal profiles.

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Section: Longitudinal Profiles and Waterfall Frequencysupporting

confidence: 93%

Section: Model Developmentmentioning

confidence: 99%

Impacts of Spontaneous Waterfall Development on Bedrock River Longitudinal Profile Morphology

Rothman,

Scheingross,

McCoy

et al. 2023

JGR Earth Surface

View full text Add to dashboard Cite

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Controls on Erosion and Cyclic Step‐Formation Upstream of Waterfalls

Inoue,

Hiramatsu,

Scheingross

et al. 2024

Geophysical Research Letters

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Waterfall retreat transmits base‐level perturbations upstream, thereby providing markers of changing climate and tectonics. In homogeneous rock, waterfalls often retreat either by direct waterfall‐face erosion or incision from repeating (‘cyclic’) steps formed above waterfalls. We lack knowledge on the conditions driving these different erosion styles, limiting our ability to predict waterfall retreat. We address this knowledge gap through flume experiments assessing how changing flow hydraulics modulates bedrock erosion. We show that, under large discharges, changes in flow hydraulics cause spatial variability in particle impact velocity, leading to cyclic step formation. As discharge decreases, both the magnitude and spatial variability of particle impact velocity decreases, causing more uniform erosion, limiting cyclic step development and potentially allowing direct erosion of the waterfall face to become the dominant retreat mechanism. These results suggest climate change and water‐resource management can alter the rate and style of waterfall retreat.

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Waterfalls Alter Reach‐Scale Fluvial Erosion Rates: Evidence From Field Data and Process Modeling

Rothman,

Scheingross,

McCoy

2024

JGR Earth Surface

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Waterfalls are often interpreted as transient, upstream‐propagating features that mark changes in external conditions. Thus, waterfalls are commonly used to infer past tectonic and climatic forcing, making understanding the controls on waterfall erosion central to predicting how external perturbations move through landscapes. Surprisingly, there exist few direct field measurements of waterfall erosion, and existing waterfall retreat measurements are rarely paired with measurements of waterfall morphology and frequency, which, theory suggests, modulate retreat rates. This lack of data limits our ability to test existing theory and explore how waterfalls alter reach‐scale bedrock erosion rates. Here, we use cosmogenic 10Be accumulated in bedrock riverbeds to measure erosion rates in fluvial reaches with varying waterfall frequency and morphology. We find that waterfall‐rich reaches erode one to five times faster than the landscape average, and that reach‐averaged erosion rates increase with increasing waterfall frequency. We develop a new, process‐based model combining waterfall and planar‐channel erosion to explore mechanistic controls on the relative erosion rate between waterfall‐rich and waterfall‐free reaches. This model predicts that reach‐averaged erosion rates increase with waterfall frequency at low sediment supply, consistent with our field measurements, but that waterfalls can also slow reach‐averaged erosion rates for high sediment supply, large grain sizes, low water discharge, or large plunge pools. Our work is consistent with previous suggestions that waterfall erosion rates may decrease in low drainage areas and can influence long‐profile morphology.

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Waterfall height sets the mechanism and rate of upstream retreat

Cited by 6 publications

References 39 publications

Impacts of Spontaneous Waterfall Development on Bedrock River Longitudinal Profile Morphology

Impacts of Spontaneous Waterfall Development on Bedrock River Longitudinal Profile Morphology

Controls on Erosion and Cyclic Step‐Formation Upstream of Waterfalls

Waterfalls Alter Reach‐Scale Fluvial Erosion Rates: Evidence From Field Data and Process Modeling

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