Using Both Free Surface Effect and Sediment Transport Mode Parameters in Defining the Morphology of River Dunes and Their Evolution to Upper Stage Plane Beds

Naqshband, Suleyman; Ribberink, Jan S.; Hulscher, Suzanne J.M.H.

doi:10.1061/(asce)hy.1943-7900.0000873

Cited by 46 publications

(96 citation statements)

References 36 publications

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“…This "loss of sediment" (the bypass fraction) contributes to the lowering of the dune heights as also observed in the flume experiments [e.g. Naqshband et al, 2014a;2014b]. Furthermore, for dunes in equilibrium under both experimental conditions (EXP1 and EXP2), the BL-model gives same lee side angles of 30° while the BL+SL-model predicts a lower lee side angle for the suspended load dominant condition (23°) compared to the bed load dominant condition (26°) [see also Smith and McLean, 1977;Bridge and Best, 1988;Amsler and Schreider, 1999;Best, 2005a and references therein].…”

Section: Model Results and Comparison With Experimental Datasupporting

confidence: 57%

“…However, Naqshband et al [2014a] showed that the relative dune length (λ/h) is not constant but linearly increases with increasing suspension number. The proposed dune length by Naqshband et al [2014a] could therefore be included in the dune evolution model. In this way, the dune evolution model's predictability will increase while the computational time will be kept to a minimum.…”

Section: Recommendationsmentioning

confidence: 97%

“…It was observed that the bed load was entirely captured in the dune with zero transport at the flow reattachment point, while a significant part of the suspended load (the bypass fraction) was advected to the downstream dune depending on the flow conditions. The bypassed suspended sediment probably plays an important role during the transition of dunes to upper stage plane beds where dunes are flattened and eventually washed out [e.g., Naqshband et al, 2014a]. Therefore, further research is needed on the quantification of this fraction during the dune transitional stages under non-equilibrium flow conditions.…”

Section: Recommendationsmentioning

confidence: 99%

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Morphodynamics of river dunes : suspended sediment transport along mobile dunes and dune development towards upper stage plane bed

Naqshband¹

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Section: Model Results and Comparison With Experimental Datasupporting

confidence: 57%

Section: Recommendationsmentioning

confidence: 97%

Section: Recommendationsmentioning

confidence: 99%

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Morphodynamics of river dunes : suspended sediment transport along mobile dunes and dune development towards upper stage plane bed

Naqshband¹

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“…Being closely related to pickup function, the near bed concentration of suspended sediment has been investigated over ripples [35] and over developing and fixed dunes [25,26,43,45]. However, only McLean et al [18], Miwa et al [22] and Miwa and Daido [21] focused on sediment entrainment over two dimensional fixed dunes.…”

Section: Introductionmentioning

confidence: 99%

“…More recently Naqshband et al [25,26] conducted simultaneous velocity and sediment concentration measurements over mobile migrating sand dunes in equilibrium using acoustic concentration and velocity profiler (ACVP). Their results show that upward sediment fluxes or sediment pickup occurred over the entire dune with large peaks on the stoss side of the dune downstream of the flow reattachment point.…”

Section: Introductionmentioning

confidence: 99%

Measurements of sediment pickup rate over dune-covered bed

Emadzadeh

Cheng

2015

Environ Fluid Mech

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Laboratory experiments were conducted to measure sediment pickup rate over two-dimensional fixed dunes. Measurements were performed over both stoss and lee sides of the dune with sediments of D 50 = 0.23, 0.44 and 0.86 mm. Flow velocity and turbulence were also measured by using an acoustic Doppler velocimeter. By analysing the experimental data, an empirical sediment pickup function based on depth-averaged flow parameters was proposed to estimate the pickup rate over the dune.Keywords Dune Á Open channel flow Á Pickup rate Á Sediment transport Á Turbulence List of symbolsA Pickup observation area (m 2 ) a 1 , a 2 ,… Constants B Channel width (m) D Sediment diameter (m) D * Dimensionless particle diameter E Sediment pickup rate (m/s) E * Dimensionless pickup rate Err Average of the relative error (%) f Function Fr * Densimetric Froude number (-) g Gravitational acceleration (m/s 2 ) Electronic supplementary material The online version of this article (H Flow depth (m) K Depth-averaged k (m 2 /s 2 ) K * Dimensionless depth-averaged turbulence kinetic energy K k Turbulence kinetic energy (m 2 /s 2 ) k s Equivalent sand roughness (m) k * Dimensionless maximum turbulence kinetic energy k max n Coefficient Q Flow discharge (m 3 /s) S Bed slope T Time period for pickup measurements (s) U Depth-averaged u (m/s) u, v, w Streamwise, spanwise and vertical velocity (m/s) u * Shear velocity (m/s) u * 0 Effective shear velocity (m/s) V T Total volume of sediment (m 3 ) x Streamwise distance (m) z Vertical distance from the bed (m) a Dune lee side angle (°) d Dune height (m) e Sediment porosity k Dune wave length (m) m Kinematic viscosity (m 2 /s) q Fluid density (kg/m 3 ) q s Sediment density (kg/m 3 ) r g Geometric standard deviation r g ¼ ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi D 84 =D 16 p s Mean bed shear stress (N/m 2 ) s * Shields parameter s * 0

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Bed load and suspended load contributions to migrating sand dunes in equilibrium

Naqshband

Ribberink

Hurther

et al. 2014

J. Geophys. Res. Earth Surf.

110

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Dunes dominate the bed of sand rivers and are of central importance in predicting flow roughness and water levels. The present study has focused on the details of flow and sediment dynamics along migrating sand dunes in equilibrium. Using a recently developed acoustic system (Acoustic Concentration and Velocity Profiler), new insights are obtained in the behavior of the bed and the suspended load transport along mobile dunes. Our data have illustrated that, due to the presence of a dense sediment layer close to the bed and migrating secondary bedforms over the stoss side of the dune toward the dune crest, the near-bed flow and sediment processes are significantly different from the near-bed flow and sediment dynamics measured over fixed dunes. It was observed that the shape of the total sediment transport distribution along dunes is mainly dominated by the bed load transport, although the bed load and the suspended load transport are of the same order of magnitude. This means that it was especially the bed load transport that is responsible for the continuous erosion and deposition of sediment along the migrating dunes. Whereas the bed load is entirely captured in the dune with zero transport at the flow reattachment point, a significant part of the suspended load is advected to the downstream dune depending on the flow conditions. For the two flow conditions measured, the bypass fraction was about 10% for flow with a Froude number (Fr) of 0.41 and 27% for flow with Froude number of 0.51. This means that respectively 90% (for the Fr = 0.41 flow) and 73% (for the Fr = 0.51 flow) of the total sediment load that arrived at the dune crests contributed to the migration of the dunes.

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Using Both Free Surface Effect and Sediment Transport Mode Parameters in Defining the Morphology of River Dunes and Their Evolution to Upper Stage Plane Beds

Cited by 46 publications

References 36 publications

Morphodynamics of river dunes : suspended sediment transport along mobile dunes and dune development towards upper stage plane bed

Morphodynamics of river dunes : suspended sediment transport along mobile dunes and dune development towards upper stage plane bed

Measurements of sediment pickup rate over dune-covered bed

Bed load and suspended load contributions to migrating sand dunes in equilibrium

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