Observations on sediment mobility in a large gravel-bed river

Mao, Luca; Surian, Nicola

doi:10.1016/j.geomorph.2009.07.015

Cited by 54 publications

(45 citation statements)

References 52 publications

(76 reference statements)

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“…The observation of mostly single step displacements holds for all observed individual floods, despite a 3-fold increase in Shields stress (τ * /τ * c1 = 3.04), demonstrating that partial and intermittent bed load transport occurred under all observed conditions. This is consistent with previous field observations by Mao and Surian (2010), who reported that partial transport occurred over a 3-fold increase in Shields stress. However, tracer displacement length distributions become increasingly skewed toward larger values with increasing flood strength ( Fig.…”

Section: Sediment Mechanicssupporting

confidence: 93%

Dynamics and mechanics of bed-load tracer particles

Phillips

Jerolmack

2014

Earth Surf. Dynam.

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Abstract. Understanding the mechanics of bed load at the flood scale is necessary to link hydrology to landscape evolution. Here we report on observations of the transport of coarse sediment tracer particles in a cobblebedded alluvial river and a step-pool bedrock tributary, at the individual flood and multi-annual timescales. Tracer particle data for each survey are composed of measured displacement lengths for individual particles, and the number of tagged particles mobilized. For single floods we find that measured tracer particle displacement lengths are exponentially distributed; the number of mobile particles increases linearly with peak flood Shields stress, indicating partial bed load transport for all observed floods; and modal displacement distances scale linearly with excess shear velocity. These findings provide quantitative field support for a recently proposed modeling framework based on momentum conservation at the grain scale. Tracer displacement is weakly negatively correlated with particle size at the individual flood scale; however cumulative travel distance begins to show a stronger inverse relation to grain size when measured over many transport events. The observed spatial sorting of tracers approaches that of the river bed, and is consistent with size-selective deposition models and laboratory experiments. Tracer displacement data for the bedrock and alluvial channels collapse onto a single curve -despite more than an order of magnitude difference in channel slope -when variations of critical Shields stress and flow resistance between the two are accounted for. Results show how bed load dynamics may be predicted from a record of river stage, providing a direct link between climate and sediment transport.

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Section: Sediment Mechanicssupporting

confidence: 93%

Dynamics and mechanics of bed-load tracer particles

Phillips

Jerolmack

2014

Earth Surf. Dynam.

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“…Furthermore, on each plot, the thickness of fine layer was measured digging a scour, and the grain size distribution of coarse sediments was calculated from the measure of b-axes of at least 30 coarse elements. The nature of the morphological units where the plots lied was characterized and classified as channels, nude bars, high bars, vegetated bars, islands and floodplains [3,4,20].…”

Section: Methodsmentioning

confidence: 99%

Riparian forest structure, vegetation cover and flood events in the Piave River

Picco

Mao

Rigon

et al. 2012

Monitoring, Stimulation, Prevention and Remediation of Dense and Debris Flows IV

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Until very recently, rivers have been considered as the result of the interaction between water and sediments, thus simplifying this very complex system. In doing so, one important component was missed. This is vegetation, namely trees growing on banks, floodplains, and bars/islands. The pattern of riparian vegetation in gravel bed rivers depends on the climate, hydrological regime, floods, sediment transport and the morphological settings of the river. Also, the marked spatial variability of density, height, species diversity, age, and rates of growth reflects the very complex nature of bed colonization, the strong influence of sequences and magnitude of floods, and the feedbacks between morphology, vegetation and hydraulics. Furthermore, a wide array of human impacts acting at either the basin or river network scales can influence substantially the morphodynamics and thus the characteristics, types and distribution of vegetation within the river corridor. The aim of the work is to analyze the relationship between the vegetation structure and the morphological characteristics of two sub-reaches of the Piave river which suffered both floods and intense and multiple human impacts especially due to dam building and inchannel gravel mining. Six cross sections were surveyed and vegetation, soil variables and sediment deposited were measured on 214 plots, (4 x 4 m each one and 10 m spaced). Each vegetation plot were recognized on a recent aerial photo (2009) and its ages were calculated performing both a multi-temporal analysis of older photos (1960, 70, 80, 91, 99, 2006 and 2009) analysis. The Piave River shows a complex pattern of vegetation distribution along the cross-sections with no clear relationship between the elevation and the plant communities. However later successional plant communities cover older surfaces and the thickness of the sand layer helps explaining differences in areas dominated by different species (e.g. Salix alba and Salix eleagnos).

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“…Thirteen kilometers downstream from the studied reach Mao and Surian (2010) observed that the lower morphological units and the 'low bars' experienced full gravel removal for high-frequency, low-magnitude floods (i.e., recurrence interval < 1 year and 1.1 year, respectively). On the 'higher bars', only partial gravel removal and fine sediment deposition was observed for a flood event with a recurrence interval of 3.5 years.…”

Section: Accepted Manuscriptmentioning

confidence: 96%