On characterization of the imbrication of armored gravel surfaces

Qin, Jie; Zhong, Dan; Wang, Guangqian; Ng, Sai Leung

doi:10.1016/j.geomorph.2012.03.012

Cited by 40 publications

(18 citation statements)

References 25 publications

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“…However, this did not improve our regressions, suggesting that other factors are likely more relevant than the local grain size distribution in determining the thickness of the active layer. For example, local hydraulics conditions (Lawless and Robert, ), grain imbrication (Qin et al , ), grain clusters (Wittenberg and Newson, ), and sediment clogging due to fine sediments (Schälchli, ) could influence the entrainment of surface grains.…”

Section: Discussionmentioning

confidence: 99%

Bed material transport estimate in large gravel‐bed rivers using the virtual velocity approach

Mao

Picco

Lenzi

et al. 2016

Earth Surf Processes Landf

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This paper reports on a first attempt of using the virtual velocity approach to assess sediment mobility and transport in two wide and complex gravel-bed rivers of northern Italy. Displacement length and virtual velocity of spray-painted tracers were measured in the field. Also, the thickness of the sediment active layer during floods was measured using scour chains and postflood morphological changes as documented by repeated survey of channel cross-sections. The effects of eight and seven floods were studied on the Tagliamento and Brenta Rivers, where 259 and 277 spray-painted areas were surveyed, respectively. In the Tagliamento River 36% of the spray-painted areas experienced partial transport, whereas in the Brenta River this accounted for 20%. Whereas, full removal/gravel deposition was observed on 37% and 26% of these areas on the Tagliamento and Brenta Rivers, respectively. The mean displacement length of particles, the thickness of the active layer and the extent of partial transport are well correlated with the dimensionless shear stress. The virtual velocity approach allowed calculation of bed material transport over a wide range of flood magnitudes. Annual coarse sediment transport was calculated up to 150 for the Tagliamento, and 30 × 10 3 m 3 yr À1 for the Brenta. The outcomes of this work highlight the relevance of partial transport condition, as it could represent more than 70% of the total bed material transported during low-magnitude floods, and up to 40% for near-bankfull events. Results confirm that bed material load tends to be overestimated by traditional formulas.The velocity of particle movement is called virtual because, by incorporating periods of both particle motion and rest, the EARTH SURFACE PROCESSES AND LANDFORMS

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Section: Discussionmentioning

confidence: 99%

Bed material transport estimate in large gravel‐bed rivers using the virtual velocity approach

Mao

Picco

Lenzi

et al. 2016

Earth Surf Processes Landf

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“…For poorly (and moderately) sorted gravel materials, the formation of a surface armor layer is generally observed under steady flow and no sediment feeding conditions (Church et al, 1998;Guney et al, 2013), which implies a bed surface coarsening (Hassan and Church, 2000), an increase in grain imbrication (Mao et al, 2011;Qin et al, 2012), and the formation of grain patterns (e.g., clusters, microforms; Marion et al, 2003;Curran, 2010). Under unsteady flows, Mao (2012) and Guney et al (2013) highlighted significant changes in gravel-bed surface organization due to the antecedent flow history and the initial degree of bed armoring and arrangement.…”

Section: Introductionmentioning

confidence: 99%

Transport of moderately sorted gravel at low bed shear stresses: The role of fine sediment infiltration

Perret

Berni

Camenen

et al. 2018

Earth Surf Processes Landf

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A reliable estimation of sediment transport in gravel‐bed streams is important for various practical engineering and biological studies (e.g., channel stability design, bed degradation/aggradation, restoration of spawning habitat). In the present work, we report original laboratory experiments investigating the transport of gravel particles at low bed shear stresses. The laboratory tests were conducted under unsteady flow conditions inducing low bed shear stresses, with detailed monitoring of the bed topography using a laser scanner. Effects of bed surface arrangements were documented by testing loose and packed bed configurations. Effects of fine sediments were examined by testing beds with sand, artificial fine sand or cohesive silt infiltrated in the gravel matrix. Analysis of the experimental data revealed that the transport of gravel particles depends upon the bed arrangement, the bed material properties (e.g., size and shape, consolidation index, permeability) and the concentration of fine sediments within the surface layer of moving grains. This concentration is directly related to the distribution of fine particles within the gravel matrix (i.e., bottom‐up infiltration or bridging) and their transport mode (i.e., bedload or suspended load). Compared to loose beds, the mobility of gravel is reduced for packed beds and for beds clogged from the bottom up with cohesive fine sediments; in both cases, the bed shear stress for gravel entrainment increases by about 12%. On the other hand, the mobility of gravel increases significantly (bed shear stress for particle motion decreasing up to 40%) for beds clogged at the surface by non‐cohesive sand particles. Copyright © 2017 John Wiley & Sons, Ltd.

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“…The surface structure of a gravel bed channel can be indicative of the flow and transport processes that have shaped the channel. Recognizing this, the characteristics and arrangement of surface grains and bed forms have been used as an indication of the range of grain sizes present in channel and flow and sediment supply histories [e.g., Grant et al ., ; Dinehart , ; Mao , ; Qin et al ., ; Ockelford and Haynes , ]. Gravel bed rivers with a range of grain sizes often develop a grain‐scale bed structure characterized as a static armor layer in which the larger grains are overrepresented on the bed surface when compared to their population in the subsurface.…”

Section: Introductionmentioning

confidence: 99%

The importance of bed sediment sand content for the structure of a static armor layer in a gravel bed river

Curran¹,

Waters

2014

JGR Earth Surface

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The surface structure of static armor layers generated from water-worked gravel bed channels was investigated with primary focus on the influence of sand content and flow rate. Flume experiments were conducted in which four sediment mixtures with sand contents between 1% and 38% were armored under one of three different flow rates. First-and second-order statistical analyses were applied to digital elevation models of unarmored, armored, and clustered bed surface areas to identify changes in surface structure. Results were combined with data from previous research to create an extended data set of armored bed surfaces. Water-worked, unarmored bed surfaces established under a dynamic equilibrium flow rate impacted the topographic variability and structure of the armored beds. Surface complexity decreased with armor formation as surface grains preferentially aligned with the flow direction. The bed surface became smoother, and where sediment mixture sand content was constant, there was greater smoothing of the surface during higher armoring flows as grains rearranged more easily. As bulk sand content increased, statistical analyses of the expanded data set showed that beds with very little sand content developed static armor layers that remained rough and had greater topographic variability than armor layers from sediments with higher sand contents. The bulk sediment sand content exerted a stronger influence over the change in surface roughness and structure upon armoring than that of the flow rate during armor formation. When combined with the knowledge of the local flow regime, the sand content may aid in predictions related to armored bed surface structure.

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On characterization of the imbrication of armored gravel surfaces

Cited by 40 publications

References 25 publications

Bed material transport estimate in large gravel‐bed rivers using the virtual velocity approach

Bed material transport estimate in large gravel‐bed rivers using the virtual velocity approach

Transport of moderately sorted gravel at low bed shear stresses: The role of fine sediment infiltration

The importance of bed sediment sand content for the structure of a static armor layer in a gravel bed river

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