The gravel-sand transition and grain size gap in river bed sediments

Dingle, Elizabeth; Kusack, Kyle M.; Venditti, Jeremy G.

doi:10.1016/j.earscirev.2021.103838

Cited by 18 publications

(21 citation statements)

References 95 publications

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“…Regarding such a decrease, early studies (Pickup, 1984; Rice & Church, 2001; Sambrook Smith & Ferguson, 1995; Venditti & Church, 2014) often associated it with a break in bed slope, which can decline 1‐10‐fold from a gravel bed to a sand bed and has commonly been observed in river systems (Dingle et al., 2021; Frings, 2011). However, in 1975, when the YXR was in (or close to) equilibrium, the bed profile had no breaks in slope (Figure 6d).…”

Section: Discussionmentioning

confidence: 99%

“…In earlier studies on GST morphodynamics, authors mostly set a constant channel width in flume experiments and numerical models (Blom et al., 2017; Toro‐Escobar et al., 2000) or chose a relatively regular channel as a prototype example (Ferguson et al., 2011; Venditti & Church, 2014). Indeed, width variability drives flow acceleration or deceleration and thus creates variations in sediment transport (Chartrand et al., 2018; Dingle et al., 2021; Toro‐Escobar et al., 2000). The presence of numerous tributary (or distributary) streams is another morphological feature of large rivers (Benda et al., 2004; Rice, 1998).…”

Section: Introductionmentioning

confidence: 99%

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Gravel‐Sand Transition of the Yangtze River: Human Disturbances, Migration Processes, and Controlling Factors

Sun

Zhou

et al. 2023

JGR Earth Surface

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Despite abundant studies on gravel‐sand transitions (GSTs), GST origin and migration in large alluvial channels characterized by significant variations in width, numerous tributary (or distributary) streams, and frequent human disturbances remain difficult to explain. Here, we take the Yangtze River as an example and use field observations and numerical modeling to make progress toward addressing GST origin and migration. The results show that the Yangtze River exhibits a non‐abrupt GST approximately 60 km long. Within the GST and the adjacent area, there are two dramatic decreases in shear stress; the upstream one induces the settlement of sand from suspension, explaining the emergence of the Yangtze River GST, whereas the downstream one induces general cessation of gravel movement. However, the deposited gravel was mostly overwhelmed by sand. We argue that these changes in shear stress in the Yangtze River depended primarily on the combined effects of width variability and distributary systems. Since 1970, the Jingjiang Meander Cut‐off, the Gezhouba Dam, and the Three Gorges Dam (TGD) have been completed in succession, repeatedly altering the flow‐sediment regime within the GST. However, the GST position remained unchanged until the TGD began operation in 2003. The stability of the GST was primarily ascribed to the sufficient upstream sand supply (grain size <0.5 mm), the resistant lithologies upstream of Zhicheng, and the Jingjiang Great Levees constraints.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Gravel‐Sand Transition of the Yangtze River: Human Disturbances, Migration Processes, and Controlling Factors

Sun

Zhou

et al. 2023

JGR Earth Surface

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“…Through their global analysis, Dingle et al. (2021) established that the only universal morphological characteristic observed in GSTs is the abrupt reduction in grain size from 5 to 10 mm gravel to sand. Given that the phenomenon is specific to these grain sizes, we elected not to scale grain size in our experiment, but instead retained these sizes and scaled the flow to produce specific transport stages of gravel and sand that are linked to their entrainment and suspension thresholds.…”

Section: Methodsmentioning

confidence: 99%

Experiments on Gravel‐Sand Transitions: Examination of Washload Deposition

Dingle

Venditti

2023

JGR Earth Surface

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“…Beyond the proximal part of the system, the depositional record more closely reflects a braid plain dominated by sand with only gravel in primary channels (Zielenski and Van Loon, 2003). This transition from gravel to sand (within a few tens or hundred meters of the mountain front; e.g., Dingle et al, 2021) is less obvious in proglacial systems, which tend to be deficient in the 1-10 mm grain size range (e.g., Maizels, 1989;Zielenski and Van Loon, 1998). Given these characteristics and the ambiguous character of proglacial facies, the best reflection of a proglacial influence on sediment transport is expected in the most proximal deposits.…”

Section: Facies Common To Proglacial Fluvial Systemsmentioning

confidence: 99%

Detecting upland glaciation in Earth’s pre-Pleistocene record

et al. 2022

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Earth has sustained continental glaciation several times in its past. Because continental glaciers ground to low elevations, sedimentary records of ice contact can be preserved from regions that were below base level, or subject to subsidence. In such regions, glaciated pavements, ice-contact deposits such as glacial till with striated clasts, and glaciolacustrine or glaciomarine strata with dropstones reveal clear signs of former glaciation. But assessing upland (mountain) glaciation poses particular challenges because elevated regions typically erode, and thus have extraordinarily poor preservation potential. Here we propose approaches for detecting the former presence of glaciation in the absence or near-absence of ice-contact indicators; we apply this specifically to the problem of detecting upland glaciation, and consider the implications for Earth’s climate system. Where even piedmont regions are eroded, pro- and periglacial phenomena will constitute the primary record of upland glaciation. Striations on large (pebble and larger) clasts survive only a few km of fluvial transport, but microtextures developed on quartz sand survive longer distances of transport, and record high-stress fractures consistent with glaciation. Proglacial fluvial systems can be difficult to distinguish from non-glacial systems, but a preponderance of facies signaling abundant water and sediment, such as hyperconcentrated flood flows, non-cohesive fine-grained debris flows, and/or large-scale and coarse-grained cross-stratification are consistent with proglacial conditions, especially in combination with evidence for cold temperatures, such as rip-up clasts composed of noncohesive sediment, indicating frozen conditions, and/or evidence for a predominance of physical over chemical weathering. Other indicators of freezing (periglacial) conditions include frozen-ground phenomena such as fossil ice wedges and ice crystals. Voluminous loess deposits and eolian-marine silt/mudstone characterized by silt modes, a significant proportion of primary silicate minerals, and a provenance from non-silt precursors can indicate the operation of glacial grinding, even though such deposits may be far removed from the site(s) of glaciation. Ultimately, in the absence of unambiguous ice-contact indicators, inferences of glaciation must be grounded on an array of observations that together record abundant meltwater, temperatures capable of sustaining glaciation, and glacial weathering (e.g., glacial grinding). If such arguments are viable, they can bolster the accuracy of past climate models, and guide climate modelers in assessing the types of forcings that could enable glaciation at elevation, as well as the extent to which (extensive) upland glaciation might have influenced global climate.

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The gravel-sand transition and grain size gap in river bed sediments

Cited by 18 publications

References 95 publications

Gravel‐Sand Transition of the Yangtze River: Human Disturbances, Migration Processes, and Controlling Factors

Gravel‐Sand Transition of the Yangtze River: Human Disturbances, Migration Processes, and Controlling Factors

Experiments on Gravel‐Sand Transitions: Examination of Washload Deposition

Detecting upland glaciation in Earth’s pre-Pleistocene record

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