Discussion of “Effects of Water Temperature on Bed-Load Movement”

Three almometers-water opacity measuring devices-emplaced perpendicular to the beach, measure instantaneously and continuously the sediment concentration across the surf zone. Most of the variance of the sand movement is centered in frequencies of less than 0.25 Hz and between 1.15 and 1.25 Hz. Modes and frequency of sand transport differ within each of the dynamic zones of the surf. The motion of sediment in the inner and outer surf zones is small and virtually independent of the deep water wave periods. Outside the breaker zone, bed load movement is somewhat coincident with the prevailing swell period. Lighter concentrations move predominantly with a 0.8-0.9 second periodicity. In the breaker zone, sand moves along the bottom with frequencies equal to that of both the swell and sea, but most of the power is in lower frequencies. In the breaker zone sand is rarely thrown into suspension. In the transition zone, sediment motion is largely by suspension with a period a little longer than the swell.

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Discussion of “Johnson on Bed-Load Movement”

Transactions of the American Society of Civil Engineers ◽

10.1061/taceat.0005497 ◽

1942 ◽

Vol 107 (1) ◽

pp. 578-593

Author(s):

Joe W. Johnson ◽

A. A. Kalinske ◽

O. G. Haywood ◽

Samuel Shulits ◽

John S. McNown

Keyword(s):

Bed Load ◽

Load Movement

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Geometrical analysis of ripple-drift cross-lamination

Canadian Journal of Earth Sciences ◽

10.1139/e69-038 ◽

1969 ◽

Vol 6 (3) ◽

pp. 383-391 ◽

Cited By ~ 17

Author(s):

Roger G. Walker

Keyword(s):

Flow Regimes ◽

High Flow ◽

The Other ◽

Bed Load ◽

Geometrical Parameters ◽

Geometrical Analysis ◽

Middle Ordovician ◽

Basin Floor ◽

Load Movement ◽

Gaspe Peninsula

The geometrical parameters of ripple-drift cross-lamination (climbing ripples) have been measured in coastal exposures of the Cloridorme Formation (Middle Ordovician turbidites of northern Gaspé Peninsula, Québec), in order to determine the factors that control the angle at which the ripples climb, and to investigate the context of the ripple-drift relative to the other sedimentary features in the Cloridorme Formation. Purely geometrical analysis shows that the angle of the stoss side is more sensitive in controlling the angle of climb than the angle of the lee side, but the single most important factor is the ratio of thickness of the stoss side and lee side laminae. When the lee laminae are about twice as thick as the stoss laminae, the angle of climb is about 30–40 degrees. If the ratio is greater than about 10, the angle of climb is reduced to about 5 degrees.The lamina thicknesses are controlled by the rate of deposition from suspension relative to the rate of bed load movement. At high flow regimes, sediment is swept onto the lee side and the angle of climb is low. In the Cloridorme Formation, the turbidites associated with the ripple-drift are proximal, and hence a rapid flattening of the basin floor gradient is suggested to cause the rapid deposition leading to ripple-drift formation.

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Experimental Study on Uniform and Mixed Bed-Load Sediment Transport under Unsteady Flow

Applied Sciences ◽

10.3390/app10062002 ◽

2020 ◽

Vol 10 (6) ◽

pp. 2002

Author(s):

Zihao Duan ◽

Jie Chen ◽

Changbo Jiang ◽

Xiaojian Liu ◽

Bingbing Zhao

Keyword(s):

Particle Size ◽

Sediment Transport ◽

Unsteady Flow ◽

Steady Flow ◽

Transport Rate ◽

Bed Load ◽

Sediment Transport Rate ◽

Particle Size Ratio ◽

Load Movement ◽

Sediment Particles

The scouring and deposition of sediment caused by unsteady flows (e.g., storm waves and floods) produces many secondary disasters. The resultant bed-load movement exhibits different transport laws compared with that by steady flow. In this study, the flume experiments were performed to study the bed-load movement under unsteady flow with different velocity skewness. The movement of uniform and non-uniform non-cohesive sediment under unsteady flow as well as the influence of the steady and unsteady flow on sediment transport rate are compared. Additionally, the non-uniform sediment transport formula of fine-to-coarse particle diameter ratio was investigated. The results showed that the sediment transport rate between uniform and non-uniform sand under the same median diameter is different. The non-uniform sediment transport rate is 1.27-, 3.19-, and 0.68-times as large as that in uniform sediment under d50 = 0.664, 1.333, and 2.639 mm under unsteady flow, respectively. For non-uniform sand, the transport rate of non-uniform sand with a larger adjacent particle size ratio (δ = 0.29) was 1.31-times greater than that of the non-uniform sand with a smaller adjacent particle size ratio (δ = 0.50). Moreover, theoretical deduction was carried out and the incipient sediment motion was analyzed from the force mechanism. A new unsteadiness parameter based on the acceleration concept was proposed. The relationship between the travel distance and velocity skewness of sediment particles was set up. The experimental results and theoretical analysis showed that sediment under unsteady flow were easier to start and transport than those under steady flow in the same flow effect. The travel distance of sediment particles was longer under unsteady flow than that under steady flow.

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