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.

Modelling Erosion and Deposition of Cohesive Sediments from Hay River, Northwest Territories, Canada

2003 ◽  
Vol 34 (1-2) ◽  
pp. 125-138 ◽  
Author(s):  
David Milburn ◽  
B.G. Krishnappan
Keyword(s):  
Shear Stress ◽  
Northwest Territories ◽  
River Sediment ◽  
Critical Shear Stress ◽  
Cohesive Sediment ◽  
Cohesive Sediments ◽  
Bed Shear Stress ◽  
Flume Experiments ◽  
Annular Flume ◽  
Erosion Processes

A large volume sample of river-bed cohesive sediment and water from Hay River, Northwest Territories, Canada was collected during a spring field program in 2000 as part of a study on under-ice movement of sediment just before breakup. Controlled laboratory experiments were subsequently conducted on the Hay River water/sediments in a rotating annular flume at Burlington, Ontario, Canada to better understand the deposition and erosion processes of cohesive sediment transport. The deposition experiments in the rotating flume confirmed that the Hay River sediment is cohesive and the critical shear stress for deposition and the rates of deposition are a function of bed shear stress and the initial concentration of the sediment in suspension. The erosion experiments provided quantitative data on the critical shear stress for erosion and the rates of erosion as a function of bed shear stress and the age of the sediment deposit. The erosion experiments also indicated that the growth of the biofilm had an influence on the erosion characteristics of the Hay River sediment. Based on the data from the rotating circular flume experiments, a modelling strategy is proposed for calculating the under-ice transport of the cohesive sediments in the Hay River.

Critical Bed-Shear Stress for Cohesive Sediment Deposition under Steady Flows

2008 ◽  
Vol 134 (12) ◽  
pp. 1767-1771 ◽  
Author(s):  
Jerome Peng-Yea Maa ◽  
Jae-Il Kwon ◽  
Kyu-Nam Hwang ◽  
Ho-Kyung Ha
Keyword(s):  
Shear Stress ◽  
Cohesive Sediment ◽  
Sediment Deposition ◽  
Bed Shear Stress ◽  
Steady Flows

Oil Erosion in an Annular Flume by Seawater of Varying Turbidities: A Critical Bed Shear Stress Approach

2002 ◽  
Vol 8 (1) ◽  
pp. 83-93 ◽  
Author(s):  
Danielle Cloutier ◽  
Carl L. Amos ◽  
Philip R. Hill ◽  
Kenneth Lee
Keyword(s):  
Shear Stress ◽  
Bed Shear Stress ◽  
Annular Flume

Erosion behaviour of fine sediment deposits

2004 ◽  
Vol 31 (5) ◽  
pp. 759-766 ◽  
Author(s):  
Bommanna G Krishnappan
Keyword(s):  
Shear Stress ◽  
Steady State ◽  
Maximum Concentration ◽  
Fine Sediment ◽  
Bed Shear Stress ◽  
Steady State Concentration ◽  
Sediment Deposits ◽  
Dilute Suspension ◽  
The Difference ◽  
State Concentration

Erosion characteristics of fine sediment deposits were studied experimentally using a rotating circular flume in the laboratory. The influence of the rate of application of bed shear stress and the structure of sediment beds was investigated. When the shear stress was applied suddenly on a bed formed by placing a thick slurry of kaolin in the flume, the concentration of the eroded sediment first increased to reach a maximum value, and then it started to decrease and finally attained a steady state value that was significantly lower than the maximum concentration (the steady state concentration value was one third of the maximum concentration value). When the shear stress was applied gradually, the behaviour was similar, but the difference between the values of the maximum concentration and steady state concentration was very small (<10%). When the shear stress was applied gradually on a bed formed by depositing a dilute suspension, the concentration increased monotonically and reached the steady state concentration without exhibiting the hump. Such a behaviour was attributed to the sorting of flocs in the settling of dilute suspension in which stronger flocs deposit first followed by weaker flocs in succession.Key words: kaolin, erosion rate, bed shear stress, bed structure, rotating circular flume, flocculation, size distribution.

Depositional Process of Fine Sediments

1982 ◽  
Vol 14 (4-5) ◽  
pp. 175-184 ◽  
Author(s):  
T Kusuda ◽  
T Umita ◽  
K Koga ◽  
H Yorozu ◽  
Y Awaya
Keyword(s):  
Shear Stress ◽  
Particle Diameter ◽  
Critical Diameter ◽  
Sediment Concentration ◽  
Suspended Particles ◽  
Cohesive Sediments ◽  
Fine Sediments ◽  
Annular Flume ◽  
Depositional Process ◽  
Depositional Rate

The main purposes of this study were to investigate the depositional properties of the typical fine less-cohesive sediments in Japanese estuaries and bays and to make it possible to estimate the amount of deposition of the sediments. Suspended fine sediment concentration depends strongly on the shear stress and a critical particle diameter exists corresponding to a certain shear stress. The suspended particles larger than the critical diameter settle down proportionally to the concentration of particles. On the other hand, the suspended particles smaller than the critical diameter are held in water without settling. The depositional properties obtained from experiments make it possible to estimate the depositional rate and amount of the sediments. In the laboratory experiments on deposition, an annular flume with a ring and a channel was used.

scholarly journals Experimental Investigation of Erosion Characteristics of Fine-Grained Cohesive Sediments

Water ◽  
2020 ◽  
Vol 12 (5) ◽  
pp. 1511
Author(s):  
Bommanna Gounder Krishnappan ◽  
Mike Stone ◽  
Steven Granger ◽  
Hari Upadhayay ◽  
Qiang Tang ◽  
...  
Keyword(s):  
Experimental Data ◽  
Shear Stress ◽  
Critical Shear Stress ◽  
River System ◽  
Cohesive Sediment ◽  
Erosion Process ◽  
Fine Grained ◽  
Annular Flume ◽  
Two Factors ◽  
Sediment Deposit

In this short communication, the erosion process of the fine, cohesive sediment collected from the upper River Taw in South West England was studied in a rotating annular flume located in the National Water Research Institute in Burlington, Ontario, Canada. This study is part of a research project that is underway to model the transport of fine sediment and the associated nutrients in that river system. The erosion experimental data show that the critical shear stress for erosion of the upper River Taw sediment is about 0.09 Pa and it did not depend on the age of sediment deposit. The eroded sediment was transported in a flocculated form and the agent of flocculation for the upper River Taw sediment may be due to the presence of fibrils from microorganisms and organic material in the system. The experimental data were analysed using a curve fitting approach of Krone and a mathematical model of cohesive sediment transport in rotating circular flumes developed by Krishnappan. The modelled and measured data were in good agreement. An evaluation of the physical significance of Krone’s fitting coefficients is presented. Variability of the fitting coefficients as a function of bed shear stress and age of sediment deposit indicate the key role these two factors play in the erosion process of fluvial cohesive sediment.

Experimental Study on the Fluid Mud Transportation Under Currents with Fluctuating Water Surface

2016 ◽  
Vol 11 (5) ◽  
pp. 982-988
Author(s):  
Chunrong Liu ◽  
◽  
Wenyu Yang ◽  
Bo Wu ◽  
Huhe Aode ◽  
...  
Keyword(s):  
Experimental Study ◽  
Shear Stress ◽  
Cross Section ◽  
Water Surface ◽  
Bed Shear Stress ◽  
Fluid Mud ◽  
Water Currents ◽  
Series Of Experiments ◽  
Surface Fluctuation ◽  
Over Time

A series of experiments conducted to study fluid mud movement in currents with a fluctuating water surface involved measuring fluid mud yield stress, bed shear stress, and water surface fluctuation. To observe fluid mud movement, we dyed a sheet of fluid mud in the water flume cross-section red. We then calculated the fluid mud transportation velocity based on mud sheet displacement over time. Experiments showed that water surface fluctuation plays an important role in fluid mud movement. Under conditions of water surface fluctuation, we were able to observe fluid mud oscillation in the case that the interface of the water and fluid mud is clear. After several oscillation cycles, fluid mud is transported downstream by water currents.

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 RESUSPENSION OF DEPOSITED COHESIVE SEDIMENT BEDS

1982 ◽  
Vol 1 (18) ◽  
pp. 95 ◽  
Author(s):  
Ashish J. Mehta ◽  
Emmanuel Partheniades
Keyword(s):  
Shear Stress ◽  
Shear Strength ◽  
Critical Shear Stress ◽  
Cohesive Sediment ◽  
Significant Feature ◽  
Bed Shear Stress ◽  
Laboratory Investigations ◽  
Shear Stength ◽  
The Difference ◽  
Consolidation Time

Surfieial layers of estuarial fine, cohesive sediment beds are deposited from flow and often are in a state of partial consolidation. A series of laboratory investigations were carried out to elucidate the erosional behavior of deposited cohesive sediment beds in flumes using kaolinite. A significant feature of such beds is that they are stratified with respect to the density and the cohesive shear stength. Under a given bed shear stress, erosion occurs at a continuously decreasing rate up to a depth at which the bed shear stress equals the shear strength. This bed shear stress is therefore also equal to the critical shear stress for erosion at that depth. An expression for the rate of erosion relating this rate to the difference between the bed shear stress and the critical shear stress has been obtained. The critical shear stress increases both with depth and with the bed consolidation time. The rate of erosion decreases with increasing consolidation time.

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