<i>In situ</i> acoustic measurements of marine gravel threshold and transport

Thorne, Peter D.; Williams, Jon J.; Heathershaw, A.D.

doi:10.1111/j.1365-3091.1989.tb00820.x

Cited by 110 publications

(83 citation statements)

References 17 publications

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“…Nakagawa and Nezu (1978) and Grass (1971Grass ( , 1982 have shown that the sweep event above the channel bed is more responsible for transfer of momentum into the boundary layer than the ejection event. In addition, Nakagawa and Nezu (1978), Thorne et al (1989), and Keshavarzy and Ball (1995) indicated that the sweep and ejection events occur more frequently than the outward interaction (quadrant I) and inward interaction (quadrant III) events. Williams (1990) and Thorne et al (1989) showed that sediment entrainment occurs most frequently during sweep events and only occasionally during outward interaction events, whereas transport of suspended sediment depends primarily on the ejection event.…”

Section: Introductionmentioning

confidence: 99%

“…In addition, Nakagawa and Nezu (1978), Thorne et al (1989), and Keshavarzy and Ball (1995) indicated that the sweep and ejection events occur more frequently than the outward interaction (quadrant I) and inward interaction (quadrant III) events. Williams (1990) and Thorne et al (1989) showed that sediment entrainment occurs most frequently during sweep events and only occasionally during outward interaction events, whereas transport of suspended sediment depends primarily on the ejection event. Additionally, Keshavarzy and Ball (1995) have shown that the magnitude of the instantaneous shear stress in a sweep event is greater than outward and inward interaction events.…”

Section: Introductionmentioning

confidence: 99%

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Investigation of turbulence flow and sediment entrainment around a bridge pier

Izadinia

Heidarpour

Schleiss

2012

Stoch Environ Res Risk Assess

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Local scour around the obstacles such as bridge pier is the result of complex interaction between turbulent flow and sediment particles at the mobile bed. The entrainment of sediment particles from the bed is stochastic in nature and it is strongly influenced by instantaneous shear stresses of the bursting process. The focus of this study is the investigation of turbulent flow and analysis of contribution of each bursting events to the Reynolds shear stress to find the dominant bursting events and also the flow structure around the circular bridge pier. The velocities around the bridge pier were measured in three dimensions using an Acoustic Doppler Velocimeter. These velocities were measured at different positions around the bridge pier and at different depths. Quadrant analysis is used to recognize the susceptible regions for sediment entrainment and deposition. According to quadrant analysis sedimentation is the dominant effect in the scour hole whereas at higher levels the erosion force becomes more important. In downstream of the pier, sediment particles are put in suspension and transported downstream due to sweep. Our results indicate that the secondary currents are more dominant in downstream of the pier, as compared to the upstream of the pier. Consequently the maximum velocity in downstream of the pier takes place in a location closer to the bed. In upstream of the pier the streamwise component of velocity becomes positive for which the universal log-law turns out to be valid.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Investigation of turbulence flow and sediment entrainment around a bridge pier

Izadinia

Heidarpour

Schleiss

2012

Stoch Environ Res Risk Assess

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“…Thus, sediment transport is episodic, with short periods of high transport and long periods of relatively feeble or no transport. Thorne et al (1989) observed that the upward high-speed fluid streaks (known as outward interactions) play an important role on sediment entrainment. It is the instantaneous increase in streamwise velocity fluctuations that generate excess bed shear stresses, governing entrainment processes.…”

Section: Introductionmentioning

confidence: 99%

Near-Bed Turbulence Characteristics at the Entrainment Threshold of Sediment Beds

2011

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This experimental study is devoted to quantification of the near-bed turbulence characteristics at an entrainment threshold of noncohesive sediments. Near the bed, the departure in the distributions of the observed time-averaged streamwise velocity from the logarithmic law is more for immobile beds than for entrainment-threshold beds. In the Reynolds shear stress distributions, a damping that occurs near the bed for sediment entrainment is higher than that for immobile beds. Quadrant analysis reveals that in the near-bed flow zone, ejections and sweeps on immobile beds cancel each other, giving rise to the outward interactions, whereas sweeps are the dominant mechanism toward sediment entrainment. The bursting duration for entrainment-threshold beds is smaller than that for immobile beds. On the other hand, the bursting frequency for entrainment-threshold beds is larger than that for immobile beds. The third-order correlations indicate that during sediment entrainment, a streamwise acceleration associated with a downward flux and advection of streamwise Reynolds normal stress is prevalent. The streamwise and the downward vertical fluxes of turbulent kinetic energy (TKE) increase with sediment entrainment. The TKE budget proves that for sediment entrainment, the pressure energy diffusion changes drastically to a negative magnitude, indicating a gain in turbulence production.

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“…The contribution of sweep and ejection events has been found to be more important than outward and inward interactions. Additionally, sweep and ejection events occur more frequently than outward and inward interactions (Nakagwa and Nezu, 1978;Thorne et al, 1989;Keshavarzi and Ball, 1997) with the average magnitude of the shear stress during a sweep event being much higher than the time averaged shear stress (Keshavarzi and Ball, 1997). A number of studies, for example, Offen and Kline (1975) and Papanicolaou et al (2002) investigated the characteristics of the bursting process and its effect on particle motion.…”

Section: A Keshavarzi Et Al: Frequency Pattern Of Turbulent Flow Anmentioning

confidence: 99%

“…Four alternative types of bursting events have been identified with each of these types having different effects on the mode and rate of sediment transport (Bridge and Bennett, 1992). Particle entrainment from the bed is closely correlated to the sweep and ejection events (Thorne et al, 1989;Nelson et al, 1995;Drake et al, 1988;Nakagwa and Nezu, 1978;Grass, 1971;Ball, 1997, 1999). The contribution of sweep and ejection events has been found to be more important than outward and inward interactions.…”

Section: A Keshavarzi Et Al: Frequency Pattern Of Turbulent Flow Anmentioning

confidence: 99%

Frequency pattern of turbulent flow and sediment entrainment over ripples using image processing

Keshavarzi

Ball

Nabavi

2012

Hydrol. Earth Syst. Sci.

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Abstract. River channel change and bed scourings are source of major environmental problem for fish and aquatic habitat. The bed form such as ripples and dunes is the result of an interaction between turbulent flow structure and sediment particles at the bed. The structure of turbulent flow over ripples is important to understand initiation of sediment entrainment and its transport. The focus of this study is the measurement and analysis of the dominant bursting events and the flow structure over ripples in the bed of a channel. Two types of ripples with sinusoidal and triangular forms were tested in this study. The velocities of flow over the ripples were measured in three dimensions using an Acoustic Doppler Velocimeter with a sampling rate of 50 Hz. These velocities were measured at different points within the flow depth from the bed and at different longitudinal positions along the flume. A CCD camera was used to capture 1500 sequential images from the bed and to monitor sediment movement at different positions along the bed. Application of image processing technique enabled us to compute the number of entrained and deposited particles over the ripples. From a quadrant decomposition of instantaneous velocity fluctuations close to the bed, it was found that bursting events downstream of the second ripple, in Quadrants 1 and 3, were dominant whereas upstream of the ripple, Quadrants 2 and 4 were dominant. More importantly consideration of these results indicates that the normalized occurrence probabilities of sweep events along the channel are in phase with the bed forms whereas those of ejection events are out of phase with the bed form. Therefore entrainment would be expected to occur upstream and deposition occurs downstream of the ripple. These expectations were confirmed by measurement of entrained and deposited sediment particles from the bed. These above information can be used in practical application for rivers where restoration is required.

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In situ acoustic measurements of marine gravel threshold and transport

Cited by 110 publications

References 17 publications

Investigation of turbulence flow and sediment entrainment around a bridge pier

Investigation of turbulence flow and sediment entrainment around a bridge pier

Near-Bed Turbulence Characteristics at the Entrainment Threshold of Sediment Beds

Frequency pattern of turbulent flow and sediment entrainment over ripples using image processing

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