Degradation of a Foreland River After the Wenchuan Earthquake, China: A Combined Effect of Weirs, Sediment Supply, and Sediment Mining

Lin, Yongpeng; An, Chenge; Zheng, Shan; Nie, Ruihua; Parker, Gary; Hassan, Marwan A.; Czapiga, Matthew J.; Fu, Xudong

doi:10.1029/2023wr035345

Cited by 3 publications

(2 citation statements)

References 56 publications

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“…Like other river interventions (e.g., channelization, dam construction, channel diversions), erosion-control measures change channel characteristics, such as hydraulic geometry, grain size, roughness, or sediment supply. Channels respond to such changes through upstream-and downstream-migrating aggradation and incision waves (An et al, 2019;Chowdhury et al, 2023;De Vriend, 2015;Y. Lin et al, 2023;Martín-Vide et al, 2020;Madej & Ozaki, 1996).…”

Section: Introductionmentioning

confidence: 99%

“…Like other river interventions (e.g., channelization, dam construction, channel diversions), erosion‐control measures change channel characteristics, such as hydraulic geometry, grain size, roughness, or sediment supply. Channels respond to such changes through upstream‐ and downstream‐migrating aggradation and incision waves (An et al., 2019; Chowdhury et al., 2023; De Vriend, 2015; Y. Lin et al., 2023; Martín‐Vide et al., 2020; Madej & Ozaki, 1996). Depending on the magnitude and spatial extent of the change, channel response may develop over centuries and extend over hundreds of kilometers (e.g., Simon & Rinaldi, 2006; Surian & Rinaldi, 2003; Yang et al., 2018; Ylla Arbós et al., 2021a).…”

Section: Introductionmentioning

confidence: 99%

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Large‐Scale Channel Response to Erosion‐Control Measures

Ylla Arbós,

Blom,

White

et al. 2024

Water Resources Research

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Erosion‐control measures in rivers aim to provide sufficient navigation width, reduce local erosion, or to protect neighboring communities from flooding. These measures are typically devised to solve a local problem. However, local channel modifications trigger a large‐scale channel response in the form of migrating bed level and sediment sorting waves. Our objective is to investigate the large‐scale channel response to such measures. We consider the lower Rhine River from Bonn (Germany) to Gorinchem (the Netherlands), where numerous erosion‐control measures have been implemented since the 1980s. We analyze measured bed level data (1999–2020) around four erosion‐control measures, comprising scour filling, bendway weirs, and two fixed beds. To get further insight on the physics behind the observed behavior, we set up an idealized one‐dimensional numerical model. Finally, we study how the geometry and spacing of the measures affect channel response. We show that erosion‐control measures reduce the sediment flux due to (a) lack of erosion over the measure and (b) sediment trapping upstream of the measure, resulting in downstream‐migrating incision waves that travel tens of kilometers at decadal timescales. When the measures are in close proximity, their downstream effects may be amplified. We conclude that, despite fulfilling erosion‐control goals at the local scale, erosion‐control measures may worsen large‐scale channel‐bed incision.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Large‐Scale Channel Response to Erosion‐Control Measures

Ylla Arbós,

Blom,

White

et al. 2024

Water Resources Research

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The roles of geometry and viscosity in the mobilization of coarse sediment by finer sediment

Hassan,

Parker,

Hassan

et al. 2024

Proc. Natl. Acad. Sci. U.S.A.

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In rivers, the addition of finer sediment to a coarser riverbed is known to increase the mobility of the coarser fraction. Two mechanisms have been suggested for this: a geometric mechanism whereby smaller sizes smooth the bed, increasing near-bed velocity and thus mobility of the larger sizes, and a viscous mechanism whereby a transitionally smooth turbulent boundary layer forms, rendering the coarser grains more mobile. Here, we report on experiments using two sediment mixtures to better understand these proposed mechanisms. In Mixture 1, we used 0.5 and 5 mm grains, and in Mixture 2, we used 2 and 20 mm grains. If the entrainment of coarse gravel by finer sediment is a purely geometric effect, then the addition of finer material should produce the same effect on the mobility of the coarser material for both mixtures because they have the same size ratio. We show that addition of finer material has a different effect on the two mixtures. We observed an increase in the mobility of the coarse fraction for both mixtures, but the increase in coarse fraction mobility for Mixture 1 was almost twice that for Mixture 2. Our experiments show that in addition to the geometric effect, enhancement of coarse gravel transport by finer sediment is also driven by a viscous effect.

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Dimensionless argument: a narrow grain size range near 2 mm plays a special role in river sediment transport and morphodynamics

Parker,

An,

Lamb

et al. 2024

Earth Surf. Dynam.

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Abstract. The grain size 2 mm is the conventional border between sand and gravel. This size is used extensively, and generally without much physical justification, to discriminate between such features as sedimentary deposit type (clast-supported versus matrix-supported), river type (gravel bed versus sand bed), and sediment transport relation (gravel versus sand). Here we inquire as to whether this 2 mm boundary is simply a social construct upon which the research community has decided to agree or whether there is some underlying physics. We use dimensionless arguments to show the following for typical conditions on Earth, i.e., natural clasts (e.g., granitic or limestone) in 20 ∘C water. As grain size ranges from 1 to 5 mm (a narrow band including 2 mm), sediment suspension becomes vanishingly small at normal flood conditions in alluvial rivers. We refer to this range as pea gravel. We further show that bedload movement of a clast in the pea gravel range with, for example, a size of 4 mm moving over a bed of 0.4 mm particles has an enhanced relative mobility compared to a clast with a size of 40 mm moving over a bed of the same 4 mm particles. With this in mind, we use 2 mm here as shorthand for the narrow pea gravel range of 1–5 mm over which transport behavior is distinct from both coarser and finer material. The use of viscosity allows the delineation of a generalized dimensionless bed grain size discriminator between “sand-like” and “gravel-like” rivers. The discriminator is applicable to sediment transport on Titan (ice clasts in flowing methane/ethane liquid at reduced gravity) and Mars (mafic clasts in flowing water at reduced gravity), as well as Earth.

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Degradation of a Foreland River After the Wenchuan Earthquake, China: A Combined Effect of Weirs, Sediment Supply, and Sediment Mining

Cited by 3 publications

References 56 publications

Large‐Scale Channel Response to Erosion‐Control Measures

Large‐Scale Channel Response to Erosion‐Control Measures

The roles of geometry and viscosity in the mobilization of coarse sediment by finer sediment

Dimensionless argument: a narrow grain size range near 2 mm plays a special role in river sediment transport and morphodynamics

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