Geometry and migration characteristics of bedforms under waves and currents

Cataño-Lopera, Yovanni A.; García, Marcelo H.

doi:10.1016/j.coastaleng.2006.03.008

Cited by 29 publications

(15 citation statements)

References 24 publications

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“…Although the rate of onshore migration of ripples has been suggested to have a tendency of increasing, as the mobility number ψ increases (Vincent & Osborne, 1993; Mori et al. , 2001; Cataño‐Lopera & García, 2006), the non‐dimensional rate of ripple migration in the present experiments had no correlation with the mobility number. It is thus conjectured that when the near‐bed velocity field undergoes a complex time history, such as involving velocity hiatuses, the peak velocity U max or the mobility number cannot be a single dominant factor regarding the rate of ripple migration.…”

Section: Resultscontrasting

confidence: 70%

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Effect of velocity hiatuses in oscillatory flow on migration and geometry of ripples: wave-flume experiments

Yamaguchi¹,

Sekiguchi²

2010

Sedimentology

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A series of wave-flume experiments was conducted to closely look at characteristics of geometry and migration of wave-generated ripples, with particular reference to the effect of velocity 'hiatuses' during which the nearbed flow velocity becomes much smaller than the threshold of sediment movement. Three types of wave patterns were generated: two types for simulating waves with intervening velocity hiatuses; and regular waves for comparison purposes. In the former two types, two different wavelengths of water waves were generated alternately in the course of a wave test: the wave with a longer wavelength was set large enough to mobilize the bottom sediment, whereas the wave with a shorter wavelength was set too small to mobilize the sediment. The former two types were designed to be different in sequence of convexity and concavity of wave patterns. The sequence with the convex-concave longer wave and successive convex-concave shorter wave was described as a 'zero-up-crossing' wave pattern, and the inverse sequence was described as a 'zero-down-crossing' wave pattern. The ripples developed under oscillatory flow with intervening hiatuses manifested the following characteristics in geometry and migration. (i) The morphological characteristics of ripples, namely wavelength, height and the ripple steepness, are unaffected by the intervening hiatuses of velocity. (ii) The directions of ripple migration under the zero-up-crossing and zero-downcrossing wave patterns corresponded well with the directions of the flow immediately before onset of the hiatuses. (iii) The observation of sand particle movement on the ripple surface indicated that, under the zero-up-crossing waves, the velocity hiatus prevents the entrained sediment cloud from being thrown onshore, and thus the sediment grains thrown onshore are fewer than those thrown offshore. As a result of the sediment movement over one wave-cycle, the net sediment transport is directed offshore under the zero-upcrossing wave pattern. (iv) The velocity of ripple migration was highly correlated with acceleration skewness. Under most of the zero-up-crossing (zero-down-crossing) wave patterns, flow acceleration skewed negative (positive) and ripples migrated offshore (onshore).

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Section: Resultscontrasting

confidence: 70%

“…, 2007) and through laboratory experiments (Inman & Bowen, 1962; Faraci & Foti, 2001, 2002; Mori et al. , 2001; Cataño‐Lopera & García, 2006). It is instructive herein to note that ripple migration may be related closely to the internal structure of ripples (Newton, 1968; De Raaf et al.…”

Section: Introductionmentioning

confidence: 99%

Effect of velocity hiatuses in oscillatory flow on migration and geometry of ripples: wave-flume experiments

Yamaguchi¹,

Sekiguchi²

2010

Sedimentology

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“…Over the past few decades, several studies have analysed the development of bedforms under unidirectional and oscillatory flows (e.g. Oost & Baas, 1994;Baas, 1999;Faraci & Foti, 2002;Admiraal et al, 2006;Cataño-Lopera & Garc ıa, 2006;Landry & Garcia, 2007). This research has provided a much improved understanding of temporally varying bedforms, with particular emphasis on the importance of initial conditions and the time required to reach equilibrium between the bed and flow.…”

Section: Introductionmentioning

confidence: 99%

A unified model for bedform development and equilibrium under unidirectional, oscillatory and combined‐flows

et al. 2014

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The development of bedforms under unidirectional, oscillatory and combined-flows results from temporal changes in sediment transport, flow and morphological response. In such flows, the bedform characteristics (for example, height, wavelength and shape) change over time, from their initiation to equilibrium with the imposed conditions, even if the flow conditions remain unchanged. These variations in bedform morphology during development are reflected in the sedimentary structures preserved in the rock record. Hence, understanding the time and morphological development in which bedforms evolve to an equilibrium stage is critical for informed reconstruction of the ancient sedimentary record. This article presents results from a laboratory flume study on bedform development and equilibrium development time conducted under purely unidirectional, purely oscillatory and combined-flow conditions, which aimed to test and extend an empirical model developed in past work solely for unidirectional ripples. The present results yield a unified model for bedform development and equilibrium under unidirectional, oscillatory and combined-flows. The experimental results show that the processes of bedform genesis and growth are common to all types of flows, and can be characterized into four stages: (i) incipient bedforms; (ii) growing bedforms; (iii) stabilizing bedforms; and (iv) fully developed bedforms. Furthermore, the development path of bedform; growth exhibits the same general trend for different flow types (for example, unidirectional, oscillatory and combined-flows), bedform size (for example, small versus large ripples), bedform shape (for example, symmetrical or rounded), bedform planform geometry (for example, two-dimensional versus three-dimensional), flow velocities and sediment grain sizes. The equilibrium time for a wide range of bed configurations was determined and found to be inversely proportional to the sediment transport flux occurring for that flow condition.

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“…In addition, combinations of colinear waves and currents have been investigated in wave tunnels [e.g., Dumas et al, 2005;Cataño Lopera and Garcia, 2006]. Bagnold [1946] pioneered the use of an oscillating plate to simulate the influence of waves on the bed, reasoning that, in the reference frame of the plate, the fluid force on the grains on the plate is very similar to that produced by harmonic waves.…”

Section: Introductionmentioning

confidence: 99%

Bed forms created by simulated waves and currents in a large flume

et al. 2007

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[1] The morphology and evolution of bed forms created by combinations of waves and currents were investigated using an oscillating plate in a 4-m-wide flume. Current speed ranged from 0 to 30 cm/s, maximum oscillatory velocity ranged from 20 to 48 cm/s, oscillation period was 8 s (except for one run with 12 s period), and the median grain size was 0.27 mm. The angle between oscillations and current was 90°, 60°, or 45°. At the end of each run the sand bed was photographed and ripple dimensions were measured. Ripple wavelength was also determined from sonar images collected throughout the runs. Increasing the ratio of current to wave (i.e., oscillatory) velocity decreased ripple height and wavelength, in part because of the increased fluid excursion during the wave period. Increasing the ratio of current to waves, or decreasing the angle between current and waves, increased the three-dimensionality of bed forms. During the runs, ripple wavelength increased by a factor of about 2. The average number of wave periods for evolution of ripple wavelength to 90% of its final value was 184 for two-dimensional ripples starting from a flat bed. Bed form orientations at the end of each run were compared to four potential controlling factors: the directions of waves, current, maximum instantaneous bed shear stress, and maximum gross bed form normal transport (MGBNT). The directions of waves and of MGBNT were equally good predictors of bed form orientations, and were significantly better than the other two factors.

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Geometry and migration characteristics of bedforms under waves and currents

Cited by 29 publications

References 24 publications

Effect of velocity hiatuses in oscillatory flow on migration and geometry of ripples: wave-flume experiments

Effect of velocity hiatuses in oscillatory flow on migration and geometry of ripples: wave-flume experiments

A unified model for bedform development and equilibrium under unidirectional, oscillatory and combined‐flows

Bed forms created by simulated waves and currents in a large flume

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