Hydraulic geometry, river sediment and the definition of bedrock channels

Turowski, Jens M.; Hovius, Niels; Wilson, Anne B.; Horng, Ming-Jame

doi:10.1016/j.geomorph.2007.10.001

Cited by 157 publications

(131 citation statements)

References 68 publications

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“…This can have significant consequences for the evolution of bedrock streams in particular, where incision rates are at least partially dependent on sediment flux (Whipple and Tucker, 2002). It is interesting to note that much of the terraced zone does not adhere to the definition of a bedrock channel presented by Turowski et al (2008) since much of the erosion acts on previous fill. In this case, the bedrockalluvial transition of Tucker and Slingerland (1996) is better defined as underload or overload, with the result being local erosion or deposition of the substrate, be it bedrock or sediment.…”

Section: Discussionmentioning

confidence: 99%

On the potential for regolith control of fluvial terrace formation in semi-arid escarpments

2016

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Abstract. Cut-fill terraces occur throughout the western Andes, where they have been associated with pluvial episodes on the Altiplano. The mechanism relating increased rainfall to sedimentation is, however, not well understood. Here, we apply a hillslope sediment model and reported cosmogenic nuclide concentrations in terraces to examine terrace formation in semi-arid escarpment environments. We focus on the Pisco river system in western Peru in order to determine probable hillslope processes and sediment transport conditions during phases of terrace formation. Specifically, we model steady-state and transient hillslope responses to increased precipitation rates. The measured terrace distribution and sediment agree with the transient predictions, suggesting strong climatic control on the cut-fill sequences in western Peru primarily through large variations in sediment load. Our model suggests that the ultimate control for these terraces is the availability of sediment on the hillslopes, with hillslope stripping supplying large sediment loads early in wet periods. At the Pisco river, this is manifest as an approximately 4-fold increase in erosion rates during pluvial periods. We suggest that this mechanism may also control terrace occurrence other semi-arid escarpment settings.

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Section: Discussionmentioning

confidence: 99%

On the potential for regolith control of fluvial terrace formation in semi-arid escarpments

2016

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“…12 and 13) is likely most relevant for the data discussed here. It is known that many actively incising bedrock rivers exhibit substantial cover at least at low flow (Meshkova et al, 2012;Tinkler and Wohl, 1998;Turowski et al, 2008bTurowski et al, , 2013, and it seems likely that for many rivers the sideward deflection length scale d is much smaller than the channel width (formally, W d, leading to W − d ≈ W ), implying substantial cover at steady state. Therefore, it can be expected that the toolsdominated approximation (Eqs.…”

Section: Comparison To Observationsmentioning

confidence: 99%

Alluvial cover controlling the width, slope and sinuosity of bedrock channels

Turowski

2018

Earth Surf. Dynam.

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Abstract. Bedrock channel slope and width are important parameters for setting bedload transport capacity and for stream-profile inversion to obtain tectonics information. Channel width and slope development are closely related to the problem of bedrock channel sinuosity. It is therefore likely that observations on bedrock channel meandering yields insights into the development of channel width and slope. Active meandering occurs when the bedrock channel walls are eroded, which also drives channel widening. Further, for a given drop in elevation, the more sinuous a channel is, the lower is its channel bed slope in comparison to a straight channel. It can thus be expected that studies of bedrock channel meandering give insights into width and slope adjustment and vice versa. The mechanisms by which bedrock channels actively meander have been debated since the beginning of modern geomorphic research in the 19th century, but a final consensus has not been reached. It has long been argued that whether a bedrock channel meanders actively or not is determined by the availability of sediment relative to transport capacity, a notion that has also been demonstrated in laboratory experiments. Here, this idea is taken up by postulating that the rate of change of both width and sinuosity over time is dependent on bed cover only. Based on the physics of erosion by bedload impacts, a scaling argument is developed to link bedrock channel width, slope and sinuosity to sediment supply, discharge and erodibility. This simple model built on sediment-flux-driven bedrock erosion concepts yields the observed scaling relationships of channel width and slope with discharge and erosion rate. Further, it explains why sinuosity evolves to a steady-state value and predicts the observed relations between sinuosity, erodibility and storm frequency, as has been observed for meandering bedrock rivers on Pacific Arc islands.

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“…While alternate relationships have been proposed [Turowski et al, 2008], the difference between them becomes negligible when p 0 > 0.6, the extent of the parameter space in the WLD. We measure the fraction of bedrock exposure and the sand discharge to capacity ratio in the Wax Lake Feeder Channel (WLFC) to test the applicability of equation (1) in a lowland river channel.…”

Section: Bedrock Erosionmentioning

confidence: 99%

The morphology and evolution of channels on the Wax Lake Delta, Louisiana, USA

Shaw

Mohrig

Whitman³

2013

JGR Earth Surface

105

108

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[1] River deltas are classic depositional systems, but a growing body of literature shows that their channel networks can be erosional. Furthermore, this erosion can attack channel beds of consolidated mud that acts as bedrock. To better understand the channel networks of natural deltas and engineered river diversions, we investigate bathymetric and planimetric change, bed cover, and sediment transport in the Wax Lake Delta (WLD) in coastal Louisiana, USA. Channels have eroded up to 40% of modern flow depth between the WLD's initiation in 1973 and 1999. Aerial image analysis shows that channels have widened by 11% between 1991 and 2009, forcing the downstream migration of islands. Channel beds are composed of 85-98% muddy bedrock, with the remainder covered by alluvial sands. Water velocity, grain size, and suspended sand concentration measurements during the 2009 spring flood show that almost all available grain sizes are transported in suspension. Flow was supply limited during this period, with the calculated sand concentration at the height of the bed load layer is 1-4 orders of magnitude smaller than predicted for saturated sand transport. We test "the cover effect" and "the tools effect" previously proposed for bedrock erosion in upland river channels. Bedrock erosion and alluvial cover are anti-correlated (the cover effect), but the observations do not closely follow previously proposed relationships. The difference in erosion rate between clear water and sand-rich water shows that abrasion by sand (the tools effect) accounts for 51% ± 56% of bedrock erosion when it is present.

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Hydraulic geometry, river sediment and the definition of bedrock channels

Cited by 157 publications

References 68 publications

On the potential for regolith control of fluvial terrace formation in semi-arid escarpments

On the potential for regolith control of fluvial terrace formation in semi-arid escarpments

Alluvial cover controlling the width, slope and sinuosity of bedrock channels

The morphology and evolution of channels on the Wax Lake Delta, Louisiana, USA

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