scholarly journals Influence of bed material size heterogeneity on bedload transport uncertainty

2008 ◽  
Vol 44 (1) ◽  
Author(s):  
Li Chen ◽  
Mark C. Stone
Keyword(s):  
Bedload Transport ◽  
Size Heterogeneity ◽  
Bed Material

Bedforms, bed material, and bedload transport in a salt-wedge estuary: Fraser River, British Columbia

1989 ◽  
Vol 26 (7) ◽  
pp. 1440-1452 ◽  
Author(s):  
R. A. Kostaschuk ◽  
M. A. Church ◽  
J. L. Luternauer
Keyword(s):  
British Columbia ◽  
River Discharge ◽  
Bedload Transport ◽  
Fraser River ◽  
Seasonal Fluctuations ◽  
Salt Wedge ◽  
Migration Rates ◽  
Material Load ◽  
Bed Material

The lower main channel of the Fraser River, British Columbia, is a sand-bed, salt-wedge estuary in which variations in velocity, discharge, and bedform characteristics are contolled by river discharge and the tides. Bed-material composition remains consistent over the discharge season and in the long term. Changes in bedform height and length follow but lag behind seasonal fluctuations in river discharge. Migration rates of bedforms respond more directly to river discharge and tidal fall than do height and length. Bedform characteristics were utilized to estimate bedload transport in the estuary, and a strong, direct, but very sensitive relationship was found between bed load and river discharge. Annual bedload transport in the estuary is estimated to be of the order of 0.35 Mt in 1986. Bedload transport in the estuary appears to be higher than in reaches upstream, possibly because of an increase in sediment movement along the bed to compensate for a reduction in suspended bed-material load produced by tidal slack water and the salt wedge.

Bed configuration and microscale processes in alluvial channels

1993 ◽  
Vol 17 (2) ◽  
pp. 123-136 ◽  
Author(s):  
André Robert
Keyword(s):  
Probabilistic Approach ◽  
Field Measurements ◽  
Bedload Transport ◽  
Transport Processes ◽  
Coarse Grained ◽  
Small Scale ◽  
Alluvial Channels ◽  
Gravel Beds ◽  
Sand And Gravel ◽  
Bed Material

Numerous recent studies on fluvial processes, both in Canada and internationally, have focused on small-scale phenomena. Investigations on the characterization of surface roughness in coarse-grained channels and its links with flow resistance and sediment transport processes have been a dominant field of research. Closely related is a second major area of investigation on turbulent flow structures in boundary layers over both sand and gravel beds and their relations with the transport of bed material. Phenomena potentially related to 'bursting' have been shown to control bedload transport processes and the concentration of sediment in suspension. Detailed investigations have also been conducted on the links between flow turbulence, bed material movement, and bed morphology at channel junctions. Finally, selective entrainment and transport of individual coarse particles have been studied from field measurements and laboratory experi ments. Emphasis has been put on bed microtopography, surface structure and texture, and on a probabilistic approach to bedload transport.

scholarly journals Grain sorting in the morphological active layer of a braided river physical model

2015 ◽  
Vol 3 (4) ◽  
pp. 577-585 ◽  
Author(s):  
P. Leduc ◽  
P. Ashmore ◽  
J. T. Gardner
Keyword(s):  
Grain Size ◽  
Numerical Modeling ◽  
Active Layer ◽  
Bedload Transport ◽  
Scale Model ◽  
Active Layer Thickness ◽  
Braided River ◽  
River Bed ◽  
Physical Scale ◽  
Bed Material

Abstract. A physical scale model of a gravel-bed braided river was used to measure vertical grain size sorting in the morphological active layer aggregated over the width of the river. This vertical sorting is important for analyzing braided river sedimentology, for numerical modeling of braided river morphodynamics, and for measuring and predicting bedload transport rate. We define the morphological active layer as the bed material between the maximum and minimum bed elevations at a point over extended time periods sufficient for braiding processes to rework the river bed. The vertical extent of the active layer was measured using 40 hourly high-resolution DEMs (digital elevation models) of the model river bed. An image texture algorithm was used to map bed material grain size of each DEM. Analysis of the 40 DEMs and texture maps provides data on the geometry of the morphological active layer and variation in grain size in three dimensions. By normalizing active layer thickness and dividing into 10 sublayers, we show that all grain sizes occur with almost equal frequency in all sublayers. Occurrence of patches and strings of coarser (or finer) material relates to preservation of particular morpho-textural features within the active layer. For numerical modeling and bedload prediction, a morphological active layer that is fully mixed with respect to grain size is a reliable approximation.

scholarly journals Estimating Sand Bedload in Rivers by Tracking Dunes: a comparison of methods based on bed elevation time-series

2019 ◽  
Author(s):  
Kate C. P. Leary ◽  
Daniel Buscombe
Keyword(s):  
Time Series ◽  
Sampling Rate ◽  
Bedload Transport ◽  
Single Beam ◽  
Bed Elevation ◽  
Sonar Systems ◽  
Optimal Beam ◽  
Field Methodology ◽  
Spatio Temporal ◽  
Bed Material

Abstract. Quantifying bedload transport is paramount to the effective management of rivers with sand or gravel-dominated bed material. However, a practical and scalable field methodology for reliably estimating bedload remains elusive. A popular approach involves calculating transport from the geometry and celerity of migrating bedforms, extracted from time-series of bed elevation profiles acquired using echosounders. Various echosounder sampling methodologies of how to extract bed elevations profiles exist. Using two sets of repeat multibeam sonar surveys with large spatio-temporal resolution and coverage, we compute bedload using three field techniques (one actual and two simulated) for acquiring bed elevation profiles: repeat multi-, single-, and multiple single-beam sonar. Significant differences in flux arise between repeat multibeam and single beam sonar. Mulitbeam and multiple single beam sonar systems can potentially yield comparable results, but the latter relies on knowledge of bedform geometries and flow that collectively inform optimal beam spacing and sampling rate. These results serve to guide design of optimal sampling, and for comparing transport estimates from different sonar configurations.

Bedload transport of fine gravel observed by motion-picture photography

1988 ◽  
Vol 192 ◽  
pp. 193-217 ◽  
Author(s):  
Thomas G. Drake ◽  
Ronald L. Shreve ◽  
William E. Dietrich ◽  
Peter J. Whiting ◽  
Luna B. Leopold
Keyword(s):  
Particle Diameter ◽  
Quantitative Information ◽  
Bedload Transport ◽  
Total Load ◽  
Fluid Forces ◽  
Large Numbers ◽  
Collective Motions ◽  
Median Diameter ◽  
Bed Material ◽  
Fine Gravel

Motion pictures taken at Duck Creek, a clear stream 6.5 m wide and 35 cm deep near Pinedale, Wyoming, provide detailed, quantitative information on both the modes of motion of individual bedload particles and the collective motions of large numbers of them. Bed shear stress was approximately 6 Pa (60 dynes cm−2), which was about twice the threshold for movement of the 4 mm median diameter fine gravel bed material; and transport was almost entirely as bedload. The displacements of individual particles occurred mainly by rolling of the majority of the particles and saltation of the smallest ones, and rarely by brief sliding of large, angular ones. Entrainment was principally by rollover of the larger particles and liftoff of the smaller ones, and infrequently by ejection caused by impacts, whereas distrainment was primarily by diminution of fluid forces in the case of rolling particles and by collisions with larger bed particles in the case of saltating ones. The displacement times averaged about 0.2−0.4 s and generally were much shorter than the intervening repose times. The collective motions of the particles were characterized by frequent, brief, localized, random sweep-transport events of very high rates of entrainment and transport, which in the aggregate transported approximately 70% of the total load moved. These events occurred 9% of the time at any particular point of the bed, lasted 1–2 s, affected areas typically 20–50 cm long by 10–20 cm wide, and involved bedload concentrations approximately 10 times greater than background. The distances travelled during displacements averaged about 15 times the particle diameter. Despite the differences in their dominant modes of movement, the 8–16 mm particles typically travelled only about 30% slower during displacement than the 2–4 mm ones, whose speeds averaged 21 cm s−1. Particles starting from the same point not only moved intermittently downstream but also dispersed both longitudinally and transversely, with diffusivities of 4.6 and 0.26 cm2 s−1, respectively. The bedload transport rates measured from the films were consistent with those determined conventionally with a bedload sampler. The 2–4 mm particles were entrained 6 times faster on finer areas of the bed, where 8–16 mm particles covered 6% of the surface area, than on coarser ones, where they covered 12%, even though 2–4 and 4–8 mm particles covered practically the same percentage areas in both cases. The 4–8 and 8–16 mm particles, in contrast, were entrained at the same rates in both cases. To within the statistical uncertainty, the rates of distrainment balanced the rates of entrainment for all three sizes, and were approximately proportional to the corresponding concentrations of bedload.

scholarly journals An overview of underwater sound generated by interparticle collisions and its application to the measurements of coarse sediment bedload transport

2014 ◽  
Vol 2 (2) ◽  
pp. 531-543 ◽  
Author(s):  
P. D. Thorne
Keyword(s):  
Bedload Transport ◽  
Transport Processes ◽  
High Temporal Resolution ◽  
Underwater Sound ◽  
Acoustic Data ◽  
The Past ◽  
Mobile Bed ◽  
Bedload Sediment ◽  
Bed Material ◽  
Interparticle Collisions

Abstract. Over the past 2 to 3 decades the concept of using sound generated by the interparticle collisions of mobile bed material has been investigated to assess if underwater sound can be utilised as a proxy for the estimation of bedload transport. In principle the acoustic approach is deemed to have the potential to provide non-intrusive, continuous, high-temporal-resolution measurements of bedload transport. It has been considered that the intensity of the sound radiated should be related to the amount of mobile material and the frequency spectrum to the size of the material. To be able to fully realise this use of acoustics requires an understanding of the parameters which control the generation of sound as particles impact. In the present work the aim is to provide scientists developing acoustics to measure bedload transport with a description of how sound is generated when particles undergo collision underwater. To investigate the properties of the sound generated, examples are provided under different conditions of impact. It is considered that providing an overview of the origins of the sound generation will provide a basis for the interpretation of acoustic data, collected in the marine environment for the study of bedload sediment transport processes.

scholarly journals Wood Retention at Inclined Bar Screens: Effect of Wood Characteristics on Backwater Rise and Bedload Transport

Water ◽  
2021 ◽  
Vol 13 (16) ◽  
pp. 2231
Author(s):  
Isabella Schalko ◽  
Virginia Ruiz-Villanueva ◽  
Fiona Maager ◽  
Volker Weitbrecht
Keyword(s):  
Sediment Traps ◽  
Bedload Transport ◽  
Large Wood ◽  
Transport Capacity ◽  
Flume Experiments ◽  
Fine Material ◽  
Mountain Catchment ◽  
Catchment Areas ◽  
Bed Material ◽  
Retention Structures

In forested mountain catchment areas, both bedload and large wood (LW) can be transported during ordinary flows. Retention structures such as sediment traps or racks are built to mitigate potential hazards downstream. Up to now, the design of these retention structures focuses on either LW or bedload. In addition, the majority of LW retention racks tend to retain both LW and bedload, while bedload transport continuity during ordinary flows is an important aspect to be considered in the design. Therefore, a series of flume experiments was conducted to study the effect of LW accumulations at an inclined bar screen with a bottom clearance on backwater rise and bedload transport. The main focus was put on testing different LW characteristics such as LW size, density, fine material, and shape (branches and rootwads), as well as a sequenced flood. The results demonstrated that a few logs (wood volume of ≈ 7 m3 prototype scale with a model scale factor of 30) are sufficient to reduce the bedload transport capacity to below 75% compared to the condition without LW. Fine material and smaller wood sizes further reduced bedload transport and increased backwater rise. In contrast, LW density and LW shape had a negligible effect. The test focusing on a sequenced flood highlighted the need for maintenance measures to avoid self-flushing of the bed material. The results of this study further indicate that an inclined bar screen may need to be adapted by considering LW characteristics in the design of the bottom clearance to enable bedload continuity during ordinary flows.

scholarly journals An overview of underwater sound generated by inter-particle collisions and its application to the measurements of coarse sediment bedload transport

2014 ◽  
Vol 2 (2) ◽  
pp. 605-633 ◽  
Author(s):  
P. D. Thorne
Keyword(s):  
Bedload Transport ◽  
Transport Processes ◽  
High Temporal Resolution ◽  
Underwater Sound ◽  
Particle Collisions ◽  
Acoustic Data ◽  
Mobile Bed ◽  
Bedload Sediment ◽  
Bed Material ◽  
Interparticle Collisions

Abstract. Over the past two to three decades the concept of using sound generated by the interparticle collisions of mobile bed material, has been investigated to assess if underwater sound can be utilised as a proxy for the estimation of bedload transport. In principle the acoustic approach is deemed to have the potential to provide non-instrusive, continuous, high temporal resolution measurements of bedload transport. It has been considered that the intensity of the sound radiated should be related to the ammount of mobile material and the frequency spectrum to the size of the material. To be able to fully realise this use of acoustics requires an understanding of the parameters which control the generation of sound as particles impact. In the present work the aim is to provide marine scientists developing acoustics to measure bedload transport with a description of how sound is generated when particles undergo collision underwater. To investigate the properties of the sound generated, examples are provided under different conditions of impact. It is considered that an understanding of the origins of the sound generation, will provide a basis for the interpretation of acoustic data collected in the marine environment, for the study of bedload sediment transport processes.

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