Nomenclature, Complexity, Semi‐Alluvial Channels and Sediment‐Flux‐Driven Bedrock Erosion

Meshkova, Lyubov; Carling, Paul A.; Buffin‐Bélanger, Thomas

doi:10.1002/9781119952497.ch31

Cited by 24 publications

(46 citation statements)

References 10 publications

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“…In some reaches, the channel is also partly confined by glaciogenic sediment along one or both banks, where the lower bank is glaciogenic and the upper bank is alluvial. In these cases, the channels do not fit existing models of partially alluvial channel morphology (Meshkova et al, 2012).…”

Section: Accepted Manuscriptmentioning

confidence: 93%

“…Channels in these glacially conditioned watersheds have beds composed of fine to coarse alluvium, thinly and/or discontinuously overlying fine-grained, cohesive till or glaciolacustrine clay that behave like erodible bedrock and constrain the vertical adjustment of the channel (Meshkova et al, 2012). In some reaches, the channel is also partly confined by glaciogenic sediment along one or both banks, where the lower bank is glaciogenic and the upper bank is alluvial.…”

Section: Accepted Manuscriptmentioning

confidence: 98%

“…In terms of the classification scheme of Meshkova et al (2012), the upper subreach qualifies as a 'bedrock-constrained' channel where the channel is bound by till underneath the bed but has mostly fully alluvial banks, while the lower subreach is both constrained and partially confined by till, which is frequently exposed in pools and along the bases of low terraces and channel banks (Figs. 5E-5G).…”

Section: River Channel Morphology and Dynamicsmentioning

confidence: 99%

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Floodplain morphology, sedimentology, and development processes of a partially alluvial channel

Thayer

Ashmore

2016

Geomorphology

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Section: Accepted Manuscriptmentioning

confidence: 93%

Section: Accepted Manuscriptmentioning

confidence: 98%

Section: River Channel Morphology and Dynamicsmentioning

confidence: 99%

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Floodplain morphology, sedimentology, and development processes of a partially alluvial channel

Thayer

Ashmore

2016

Geomorphology

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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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“…Bedrock or semi-alluvial channels (see Meshkova et al, 2012) received little attention in the literature for much of the 20th century due to the concentration of human interests in lowland alluvial valleys (Halwas and Church, 2002;Toone et al, 2014). The relatively recent recognition of steep headwater channels as critical habitats and sediment sources, as well as their role in landscape evolution, has encouraged research in recent decades, with a particular focus on process-based morphology (Montgomery and Buffington, 1997), the nature and rates of bedrock incision (Sklar and Dietrich, 1998;Tinkler and Wohl, 1998), and the numerical modelling of sediment transport and bedrock incision (see Turowski et al, 2007Turowski et al, , 2009Lague, 2010).…”

Section: Importance Of Bedrock Channel Morphology and Processesmentioning

confidence: 99%

Hitting rock bottom: morphological responses of bedrock-confined streams to a catastrophic flood

et al. 2015

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Abstract. The role of extreme events in shaping the Earth's surface is one that has held the interests of Earth scientists for centuries. A catastrophic flood in a tectonically quiescent setting in eastern Australia in 2011 provides valuable insight into how semi-alluvial channels respond to such events. Field survey data (3 reaches) and desktop analyses (10 reaches) with catchment areas ranging from 0.5 to 168 km 2 show that the predicted discharge for the 2011 event ranged from 415 to 933 m 3 s −1 , with unit stream power estimates of up to 1077 W m −2 . Estimated entrainment relationships predict the mobility of the entire grain-size population, and field data suggest the localised mobility of boulders up to 4.8 m in diameter. Analysis of repeat lidar data demonstrates that all reaches (field and desktop) were areas of net degradation via extensive scouring of coarse-grained alluvium with a strong positive relationship between catchment area and normalised erosion (R 2 = 0.72-0.74). The extensive scouring in the 2011 flood decreased thalweg variance significantly removing previous step pools and other coarse-grained in-channel units, forming lengths of plane-bed (cobble) reach morphology. This was also accompanied by the exposure of planar bedrock surfaces, marginal bedrock straths and bedrock steps. Post-flood field data indicate a slight increase in thalweg variance as a result of the smaller 2013 flood rebuilding the alluvial overprint with pool-riffle formation. However, the current form and distribution of channel morphological units does not conform to previous classifications of bedrock or headwater river systems. This variation in postflood form indicates that in semi-alluvial systems extreme events are significant for re-setting the morphology of in-channel units and for exposing the underlying lithology to ongoing erosion.

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Nomenclature, Complexity, Semi‐Alluvial Channels and Sediment‐Flux‐Driven Bedrock Erosion

Cited by 24 publications

References 10 publications

Floodplain morphology, sedimentology, and development processes of a partially alluvial channel

Floodplain morphology, sedimentology, and development processes of a partially alluvial channel

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

Hitting rock bottom: morphological responses of bedrock-confined streams to a catastrophic flood

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