scholarly journals Critical conditions of bed sediment entrainment due to debris flow

2004 ◽  
Vol 4 (3) ◽  
pp. 469-474 ◽  
Author(s):  
M. Papa ◽  
S. Egashira ◽  
T. Itoh
Keyword(s):  
Shear Stress ◽  
Debris Flow ◽  
Erosion Rate ◽  
Sediment Concentration ◽  
Critical Conditions ◽  
Bed Shear Stress ◽  
Bed Sediment ◽  
Sediment Size ◽  
Flume Tests ◽  
Sediment Entrainment

Abstract. The present study describes entrainment characteristics of bed material into debris flow, based on flume tests, numerical and dimensional analyses. Flume tests are conducted to investigate influences of bed sediment size on erosion rate by supplying debris flows having unsaturated sediment concentration over erodible beds. Experimental results show that the erosion rate decreases monotonically with increase of sediment size, although erosion rate changes with sediment concentration of debris flow body. In order to evaluate critical condition of bed sediment entrainment, a length scale which measures an effective bed shear stress is introduced. The effective bed shear stress is defined as total shear stress minus yield stress on the bed surface. The results show that critical entrainment conditions can be evaluated well in terms of Shields curve using the effective bed shear stress instead of a usual bed shear stress.

scholarly journals MAGNITUDE OF THE B-FACTOR UNDER WAVE ACTION

1986 ◽  
Vol 1 (20) ◽  
pp. 67
Author(s):  
J. Van de Graaff ◽  
R.C. Steijn
Keyword(s):  
Velocity Distribution ◽  
Water Depth ◽  
Sediment Concentration ◽  
Wave Action ◽  
Practical Applications ◽  
Wave Flume ◽  
Sediment Size ◽  
Flume Tests ◽  
Waves And Currents ◽  
The Moment

The sediment transport due to waves and currents depends on the distribution of sediment concentration and on the distribution of the velocity over the water depth. Our knowledge of both phenomena for practical applications is still rather poor. Some results of wave flume tests concerning the distribution of sediment concentrations due to wave action will be discussed. It turns out that the sediment size of the bottom material has a rather unexpected effect hereupon. With respect to the velocity distribution only some qualitative remarks can be made at the moment.

In situ observation of the water-sediment interface in combined sewers, using endoscopy

2003 ◽  
Vol 47 (4) ◽  
pp. 11-18 ◽  
Author(s):  
C. Oms ◽  
M.-C. Gromaire ◽  
G. Chebbo
Keyword(s):  
Shear Stress ◽  
Small Diameter ◽  
Organic Layer ◽  
In Situ Observation ◽  
Bed Shear Stress ◽  
Bed Sediment ◽  
Plastic Tube ◽  
Non Destructive ◽  
Sediment Interface

A new method for water-sediment interface observation has been designed. This system is based on a small diameter endoscope protected by a graduated plastic tube. It makes it possible to visualise in a non-destructive manner the sediments and the water-sediment interface. The endoscope was used to investigate Le Marais catchment (Paris): an immobile organic layer was observed at the water-sediment interface. This layer appears in pools of gross bed sediment, at the upstream of collectors, in zones where velocity is slow and where bed shear stress is less than 0.03 N/m2.

Bed shear stress and sediment entrainment potential for breaking of internal solitary waves

2020 ◽  
Vol 135 ◽  
pp. 103475 ◽  
Author(s):  
Giovanni la Forgia ◽  
Talia Tokyay ◽  
Claudia Adduce ◽  
George Constantinescu
Keyword(s):  
Shear Stress ◽  
Solitary Waves ◽  
Internal Solitary Waves ◽  
Bed Shear Stress ◽  
Sediment Entrainment

Effect of Bed Sediment Entrainment on Debris-Flow Resistance

2014 ◽  
Vol 140 (1) ◽  
pp. 115-120 ◽  
Author(s):  
Mi Tian ◽  
Kai-heng Hu ◽  
Chao Ma ◽  
Fa-hong Lei
Keyword(s):  
Debris Flow ◽  
Flow Resistance ◽  
Bed Sediment ◽  
Sediment Entrainment

A simplified approach to computing flow and bedload along gravel dune-like bedforms

2015 ◽  
Vol 42 (6) ◽  
pp. 367-376
Author(s):  
S. Attar ◽  
S. Samuel Li
Keyword(s):  
Shear Stress ◽  
Flow Separation ◽  
High Efficiency ◽  
Bedload Transport ◽  
Limiting Factor ◽  
Shear Stresses ◽  
Bed Shear Stress ◽  
Simplified Approach ◽  
Sediment Size ◽  
Good Potential

River dunes are important bedforms. Problems associated with the development and evolution of dune bedforms include increased flood risks, channel erosion, and damage to fish habitats. The purpose of this paper is to investigate the near-bed flow structure and bedload transport along gavel dune-like bedforms. The velocity field is computed using a relatively simple multi-layer hydrodynamic model, with a parameterization of flow separation in the leeside of dunes. The computation is of high efficiency and avoids uncertainties caused by flow separation. Fractional transport rates for a sediment mixture of sands and gravel are calculated using surface-based techniques. The computed flow velocities and bed shear stresses are in good comparison with acoustic Doppler velocimeter measurements. Bedload transport is shown to increase non-linearly with distance toward the dune crest and reach the maximum at the crest. This implies that dune-length averaged bed shear stress is not suitable for bedload calculations. At low discharges, the bed shear stress is the limiting factor, resulting in insignificant bedload. At high discharges when the bed shear stress exceeds a threshold, the effect of sediment-grain hiding and sediment-size availability are important for bedload calculations. The discharge–transport relationship is highly non-linear. This paper has demonstrated selective transport and potential dune surface coarsening. The simplified modelling approach has a good potential for application to field conditions.

Fractal dimensions of cohesive sediment during settling in steady state flow with different initial sediment concentrations

2005 ◽  
Vol 32 (4) ◽  
pp. 658-664 ◽  
Author(s):  
M Stone ◽  
B G Krishnappan
Keyword(s):  
Shear Stress ◽  
Steady State ◽  
Suspended Solids ◽  
Fractal Dimensions ◽  
Sediment Concentration ◽  
Cohesive Sediment ◽  
Image Analysis System ◽  
Bed Shear Stress ◽  
Annular Flume ◽  
Over Time

Morphology of particle populations of cohesive sediment were examined during settling experiments in an annular flume with different initial sediment concentrations (200 and 350 mg/L) at constant bed shear stress (0.121 N/m2) using fractal dimensions. The area, longest axis, and perimeter of suspended solids were measured with light microscopy and an image-analysis system to determine three fractal dimensions (D, D1, D2). The ratio between the initial and steady state (time T = 300 min) sediment concentration was 0.54 for both experimental runs and is a function of bed shear stress, not the initial sediment concentration. The fractal dimension D changed from 1.32 at the start of the experiment to 1.36 at steady state, which represents an increase in shape irregularity of larger particles over time compared with smaller particles. At steady state, D1 and D2 were 1.19 and 1.66, respectively. Small increases in D1 and D2 over time indicated a change in morphology towards longer and more elongated particles. The D2 measurements in the present study indicate that differential sedimentation is the predominant flocculation mechanism of cohesive sediments in the flume settling experiments. Fractal dimensions of suspended solids were not significantly different at steady state as a function of initial sediment concentration.Key words: particle morphology, fractal dimensions, cohesive sediment, flocculation, deposition, annular flume.

scholarly journals Erosion of fine sediments from a rough bed

2018 ◽  
Vol 40 ◽  
pp. 05058
Author(s):  
Michele Trevisson ◽  
Olivier Eiff
Keyword(s):  
Shear Stress ◽  
Sediment Supply ◽  
Critical Conditions ◽  
Bed Shear Stress ◽  
Flow Conditions ◽  
Flume Experiments ◽  
Gravel Beds ◽  
Fine Sediments ◽  
Sediment Bed ◽  
Rough Bed

Gravel beds in river systems represent important aquatic habitats, which may be endangered by the introduction of large amounts of fine sediments. In order to better understand the interaction between fine sediments and coarse immobile beds in sediment supply-limited systems, a series of flume experiments was conducted. The main goal was to determine under what conditions erosion stops. The experiments were performed over a bed of regularly arranged spheres. Plastic particles were taken as sediment and the erosion was investigated under uniform flow conditions for variable bed shear stress conditions just above critical conditions. The system was observed to behave in two different ways: with higher bed shear stress fine sediments were completely washed out, whilst with lower stress the sediment bed reached a stable level just above the equator of the spheres.

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