Ripples on Stream Bed

Raudkivi, Arved J.

doi:10.1061/(asce)0733-9429(1997)123:1(58)

Cited by 111 publications

(91 citation statements)

References 16 publications

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“…The most comprehensive predictor for current-generated, wavegenerated and combined-flow bedforms was proposed by Soulsby et al (2012). Other widely used bedform predictors were proposed by Haque & Mahmood (1985), Baas (1993), van Rijn (1993, Julien & Klaassen (1995), Raudkivi (1997) and Karim (1999) for unidirectional currents, and by Nielsen (1981), van Rijn (1993), Wiberg & Harris (1994), Malarkey & Davies (2003), Grasmeijer & Kleinhans (2004), Williams et al (2004Williams et al ( , 2005, Camenen & Larson (2006), Yan et al (2008), Camenen (2009), Pedocchi & Garcia (2009) and Nelson et al (2013) for oscillatory currents.…”

Section: Bedforms In Non-cohesive Sedimentmentioning

confidence: 99%

Predicting bedforms and primary current stratification in cohesive mixtures of mud and sand

Baas

Best

Peakall

2015

JGS

158

253

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The use of sedimentary structures as indicators of flow and sediment morphodynamics in ancient sediments lies at the very heart of sedimentology, and allows reconstruction of formative flow conditions generated in a wide range of grain sizes and sedimentary environments. However, the vast majority of past research has documented and detailed the range of bedforms generated in essentially cohesionless sediments that lack the presence of mud within the flow and within the sediment bed itself. Yet most sedimentary environments possess fine-grained sediments and recent work has shown how the presence of this fine sediment may substantially modify the fluid dynamics of such flows. It is increasingly evident that understanding the influence of mud, and the presence of cohesive forces, is essential to permit a fuller interpretation of many modern and ancient sedimentary successions. In this paper, the present state of knowledge on the stability of current- and wave-generated bedforms and their primary current stratification is reviewed, and a new extended bedform phase diagram is presented that summarizes the bedforms generated in mixtures of sand and mud under rapidly decelerated flows. This diagram provides a phase space using the variables of yield strength and grain mobility as the abscissa and ordinate axes, respectively, and defines the stability fields of a range of bedforms generated under flows that have modified fluid dynamics owing to the presence of suspended sediment within the flow. Our results also present unique data on a range of bedforms generated in such flows, whose recognition is essential to help interpret such deposits in the ancient sedimentary record, including the following: (1) heterolithic stratification, comprising alternating laminae or layers of sand and mud; (2) the preservation of low-amplitude bed-waves, large current ripples and bed scours with intrascour composite bedforms; (3) low-angle cross-lamination and long lenses and streaks of sand and mud formed by bed-waves; (4) complex stacking of reverse bedforms, mud layers and low-angle cross-lamination on the upstream face of bed scours; (5) planar bedding comprising stacked mud–sand couplets. Furthermore, the results shown herein demonstrate that flow variability is not required to produce deposits consisting of interbedded sand and muds, and that the nature of flaser, wavy and lenticular bedding ( sensu Reineck & Wunderlich 1968) may also need reconsideration in the deposits of such sediment-laden flows.

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Section: Bedforms In Non-cohesive Sedimentmentioning

confidence: 99%

Predicting bedforms and primary current stratification in cohesive mixtures of mud and sand

Baas

Best

Peakall

2015

JGS

158

253

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“…Where, V = Flow velocity, d= flow depth, s = specific gravity of particle and d 50 = mean diameter of particle.It was found that N * < 80 defines the occurrence of ripples for most of the observed flows with ripple beds in the laboratory data Guy et al (1966) and (R * = 10-20 for ripples), proposed by Raudkivi (1997 …”

Section: Introductionmentioning

confidence: 87%

Prediction of Flow Regimes and Bedform Migration

Deb¹

2017

ijetst

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“…In these studies, the geometry of bed ripples was found to be function turbulent flow structure and shear stress parameters (Hurthet et al, 2007(Hurthet et al, , 2011Thorn et al, 2009). Raudkivi (1997) pointed out that the ripples and vortices within the shear layer are affected by the flow depth, velocity distribution and shear stress on the bed. Despite more than three decades of investigation, there is still insufficient information to characterize ripple-flow interaction in adequate detail and over a range of turbulent flow conditions.…”

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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Ripples on Stream Bed

Cited by 111 publications

References 16 publications

Predicting bedforms and primary current stratification in cohesive mixtures of mud and sand

Predicting bedforms and primary current stratification in cohesive mixtures of mud and sand

Prediction of Flow Regimes and Bedform Migration

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

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