Influence of Rarely Mobile Boulders on Channel Width and Slope: Theory and Field Application

Nativ, Ronit; Turowski, Jens M.; Goren, Liran; Laronne, Jonathan B.; Ôta, Yôko

doi:10.1029/2021jf006537

Cited by 6 publications

(12 citation statements)

References 100 publications

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“…A positive relationship between boulder cover fraction and slope might be expected where boulders are assumed to be immobile ( 18 , 26 , 45 ), due to bed armoring and the extraction of momentum from flows due to increased drag ( 38 ). Our boulder transport stage estimates (Fig.…”

Section: Discussionmentioning

confidence: 99%

“…Second, channel width is sensitive to the presence and orientation of the fracture sets associated with dominant metamorphic fabrics ( 49 , 50 ), and channels can abruptly narrow when cutting across the strike of regional fabrics. Third, local inputs of coarse sediment from landslides can drive channel widening due to bed armoring in cases where boulders are infrequently mobile ( 26 , 51 ). Because we do not observe any relationship between channel width and grain size or cover in Taiwan, this factor is likely limited to segments with high immobile boulder cover.…”

Section: Discussionmentioning

confidence: 99%

“…Thus, measurements of channel geometry and sediment cover have typically been limited by field accessibility and time constraints. Advances in high-resolution remote sensing using uncrewed aerial vehicles (UAVs) and structure-from-motion photogrammetry now make it possible to bridge the gap between local field surveys of bedrock channels and regional models ( 25 , 26 ).…”

Section: Introductionmentioning

confidence: 99%

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Rock properties and sediment caliber govern bedrock river morphology across the Taiwan Central Range

Carr,

DiBiase,

Yeh

et al. 2023

Sci. Adv.

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Feedbacks between surface and deep Earth processes in collisional mountain belts depend on how erosion and topographic relief vary in space and time. One outstanding unknown lies in how rock strength influences bedrock river morphology and thus mountain relief. Here, we quantify boulder cover and channel morphology using uncrewed aerial vehicle surveys along 30 kilometers of bedrock-bound river corridors throughout the Taiwan Central Range where regional gradients in rock properties relate to tectonic history. We find that boulder size systematically increases with increasing metamorphic grade and depth of exhumation. Boulder size correlates with reach-scale channel steepness but does not explain observations of highly variable channel width. Transport thresholds indicate that rivers are adjusted to mobilize boulders and are well in excess of the threshold to transport gravel and cobbles, as previously assumed. The linkage between metamorphic history, boulder size, and channel steepness reveals how rock properties can influence feedbacks between tectonics and topography throughout the life span of a mountain range.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Rock properties and sediment caliber govern bedrock river morphology across the Taiwan Central Range

Carr,

DiBiase,

Yeh

et al. 2023

Sci. Adv.

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“…In addition, the surveyed river exhibits a series of protruding roughness elements that likely form standing waves. This has been shown (Nativ et al, 2022;Schmandt et al, 2013Schmandt et al, , 2017 to generate seismic signals not accounted for by the turbulence model (Gimbert et al, 2014). For those reasons, the water level inversion 𝐴𝐴 𝐴 is not accurate in our setting, and we do not further consider it in the frame of this study.…”

Section: Model Applicationmentioning

confidence: 96%

Anatomy of an Alpine Bedload Transport Event: A Watershed‐Scale Seismic‐Network Perspective

Antoniazza,

Dietze,

Mancini

et al. 2023

JGR Earth Surface

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The way Alpine rivers mobilize, convey and store coarse material during high‐magnitude events is poorly understood, notably because it is difficult to obtain measurements of bedload transport at the watershed scale. Seismic sensor data, evaluated with appropriate seismic physical models, can provide that missing link by yielding time‐varying estimates of bedload transport albeit with non‐negligible uncertainty. Low cost and ease of installation allows for networks of sensors to be deployed, providing continuous, watershed‐scale insights into bedload transport dynamics. Here, we deploy a network of 24 seismic sensors to estimate coarse material fluxes in a 13.4 km2 Alpine watershed during a high‐magnitude transport event. First, we benchmark the seismic inversion routine with an independent time‐series of bedload transport obtained with a calibrated acoustic system. Then, we apply the procedure to the other seismic sensors across the watershed. Propagation velocities derived from cross‐correlation analysis between spatially‐consecutive bedload transport time‐series were too high with respect to typical bedload transport velocity suggesting that a faster‐moving water wave (re‐)mobilizes local coarse material. Spatially‐distributed estimates of bedload transport reveal a relative inefficiency of Alpine watersheds in evacuating coarse material, even during a relatively infrequent high‐magnitude bedload transport event. Significant inputs estimated for some tributaries were rapidly attenuated as the main river crossed less hydraulically‐efficient reaches. Only a small proportion of the total amount of material mobilized in the watershed was exported at the outlet. Multiple periods of competent flows are likely necessary to evacuate coarse material mobilized throughout the watershed during individual bedload transport events.

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“…The presence of boulders influences channel geometry and scaling relations including width, depth and local slope (Church & Zimmermann, 2007;Nativ et al, 2022;Shobe et al, 2016Shobe et al, , 2018.…”

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confidence: 99%

Unravelling fluvial versus glacial legacy controls on boulder‐bed river geomorphology for semi‐alluvial rivers in Fennoscandia

Mason,

Polvi

2023

Earth Surf Processes Landf

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River management is founded on predictable self‐organisation between river form and catchment controls in alluvial rivers. However, a substantial proportion of rivers are not fully alluvial. In previously glaciated landscapes, boulder‐rich glacial till influences river channel form and process. Increasing interest in nature‐ and process‐based river restoration requires knowledge of pre‐disturbance natural processes, which does not exist for semi‐ and non‐alluvial rivers in Fennoscandia. We aimed to determine the role of Pleistocene glaciation and subsequent deglaciation versus Holocene fluvial processes in controlling channel form of boulder‐bed rivers in Fennoscandia. We quantified morphological characteristics of northern Swedish boulder‐bed rivers, in which channel morphology was minimally impacted by humans, and used the degree of alluvial signatures to infer fluvial and legacy glacial controls. We conducted surveys of reach‐scale channel geometry, boulder and wood distributions and catchment characteristics for 20 reference reaches (drainage area: 11–114 km2). Reaches ranged in slope from 1% to 8% and were extremely diverse in channel geometry. Rivers showed little self‐organisation at the reach scale; no association exists between channel width and channel slope or bed sediment size. Boulders were rarely clustered into bedforms (e.g., step‐pools) typical of boulder‐bed mountain rivers. Drainage area was positively correlated with channel capacity but not channel width, slope or sediment size. Channel boulder density was best predicted by surveys of terrestrial boulders. Consequently, channel geometry, boulder size and the distribution of boulders were primarily controlled by legacy glacial conditioning rather than current fluvial processes, with some alluvial adjustment of smaller particles within the boulder template. Therefore, restoration of semi‐alluvial rivers should take into account local sediment and geomorphic conditions rather than use management principles built for fully alluvial rivers.

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Influence of Rarely Mobile Boulders on Channel Width and Slope: Theory and Field Application

Cited by 6 publications

References 100 publications

Rock properties and sediment caliber govern bedrock river morphology across the Taiwan Central Range

Rock properties and sediment caliber govern bedrock river morphology across the Taiwan Central Range

Anatomy of an Alpine Bedload Transport Event: A Watershed‐Scale Seismic‐Network Perspective

Unravelling fluvial versus glacial legacy controls on boulder‐bed river geomorphology for semi‐alluvial rivers in Fennoscandia

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