The transport of sand and dust by wind is a potent erosional force, creates sand dunes and ripples, and loads the atmosphere with suspended dust aerosols This article presents an extensive review of the physics of wind-blown sand and dust on Earth and Mars Specifically, we review the physics of aeolian saltation, the formation and development of sand dunes and ripples, the physics of dust aerosol emission, the weather phenomena that trigger dust storms, and the lifting of dust by dust devils and other small-scale vortices We also discuss the physics of wind-blown sand and dune formation on Venus and Titan

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The physics of wind-blown sand and dust

The transport of sand and dust by wind is a potent erosional force, creates sand dunes and ripples, and loads the atmosphere with suspended dust aerosols. This paper presents an extensive review of the physics of wind-blown sand and dust on Earth and Mars. Specifically, we review the physics of aeolian saltation, the formation and development of sand dunes and ripples, the physics of dust aerosol emission, the weather phenomena that trigger dust storms, and the lifting of dust by dust devils and other small-scale vortices. We also discuss the physics of wind-blown sand and dune formation on Venus and Titan.

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The subject of ocean turbulence is in a state of discovery and development with many intellectual challenges. This book describes the principal dynamic processes that control the distribution of turbulence, its dissipation of kinetic energy and its effects on the dispersion of properties such as heat, salinity, and dissolved or suspended matter in the deep ocean, the shallow coastal and the continental shelf seas. It focuses on the measurement of turbulence, and the consequences of turbulent motion in the oceanic boundary layers at the sea surface and near the seabed. Processes are illustrated by examples of laboratory experiments and field observations. The Turbulent Ocean provides an excellent resource for senior undergraduate and graduate courses, as well as an introduction and general overview for researchers. It will be of interest to all those involved in the study of fluid motion, in particular geophysical fluid mechanics, meteorology and the dynamics of lakes.

https://assets.cambridge.org/97805218/35435/frontmatter/9780521835435_frontmatter.pdf

The Turbulent Ocean

ASCE Manual 54 , Sedimentation Engineering, prepared under the leadership of Professor Vito A. Vanoni, has provided guidance to theoreticians and practitioners’ world wide on the primary topic of sediment problems involved in the development, use, and conservation of water and land resources. First published in 1975, Manual 54 gives an understanding of the nature and scope of sedimentation problems, of the methods for their investigation, and of practical approaches to their solution. It is essentially a textbook on sedimentation engineering, as its title accurately refl ects. Manual 5 4 was the fi rst and most comprehensive text of its kind and has been circulated throughout the world for the past 30 years as the most complete reference on sedimentation engineering in the world. It has recently been published again as the Classic Edition (Vanoni 2006). In the spirit of its predecessor, this chapter of Manual of Practice 110 , Sedimentation Engineering, aims at presenting the state of the art concerning the hydraulics of sediment transport in fl uvial systems based on the knowledge gained in the last three decades. A concerted effort is made to relate the mechanics of sediment transport in rivers and by turbidity currents to the morphodynamics of lake and reservoir sedimentation, including the formation of fl uvial deltas.

Sediment Transport and Morphodynamics

Recent field observations from several shelf environments show that gravity-driven transport within negatively buoyant layers is an important mode of fine sediment transport across continental shelves. Specifically, Dick Sternberg, along with his students and colleagues, stimulated a paradigm shift by reporting strong evidence from the Amazon and Eel shelves that hyperpycnal layers do not require autosuspension for sustenance but can be initiated by sediment flux convergence and supported by wave and current-induced suspension within relatively thin near-bed layers. As these layers move downslope under the influence of gravity, they may deposit sediment in response to decreases in bottom orbital velocities, near-bed current velocity, and/or bed slope. Direct or indirect evidence for wave or current supported sediment gravity flows has recently been reported off other high-load rivers including the Atchafalaya, Fly, Ganges–Brahmaputra, Klamath, Mad, Mississippi, Po, Rhone, Waiapu, Waipaoa, Yangtze, and Yellow among others. Growing evidence from observational and modeling studies suggests that flux convergence followed by wave and current supported gravity driven transport is a primary cause of across-shelf transport and emplacement of flood deposits on many muddy shelves and may be a major contributor to and control on the large-scale formation and morphology of subaqueous deltas and shelf clinoforms. Recent and ongoing studies on this subject are synthesized in this paper and recommendations are offered for further study.

Gravity-driven sediment transport on continental shelves: A status report

Phase lags in oscillatory sheet flow: experiments and bed load modelling

For the first time, detailed measurements of sediment concentrations and grain velocities inside the sheet flow layer under prototype surface gravity waves have been carried out in combination with measurements of suspension processes above the sheet flow layer. Experiments were performed in a large-scale wave flume using natural sand. Sand transport under high waves in shallow water is mainly contained within the so-called “sheet flow layer,” a thin layer (10–60 grain diameters) in which the volume concentration of sand decreases by an order of magnitude from a value near 0.6 at the stationary bed. The thickness of the layer varies over a wave cycle and the maximum thickness increases with increasing peak Shields stress. The concentrations within the sheet flow layer vary approximately synchronously with the orbital velocity measured by an Acoustic Doppler Velocimeter (ADV) located 0.1 m above the bed, with typical phase lags of 0–π/5. In contrast, the suspended sediment concentrations a few centimeters and higher above the bed exhibit larger phase lags. Grain velocities were successfully measured in the middle and upper portions of the sheet flow layer around the time of their maximums. These velocities increased weakly with elevation from approximately 50% to 70% of the velocity outside the wave boundary layer. The observations are compared to previous experimental work and are found to be mainly consistent with observations in steady unidirectional flows and in oscillating water tunnels (OWTs), although differences in the suspended sediment concentration and the total sediment transport rate are apparent. Observations are also compared to two very different models: a 1DV suspension model for oscillatory flow with enhanced boundary roughness and a two-phase collisional grain flow model for steady unidirectional flow. While the suspension model describes the velocity profile fairly well and the collisional model describes the concentration profile well, neither model accurately predicts both the velocity and the concentration and therefore the sediment flux over the full vertical extent of the sheet flow.

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Sheet flow dynamics under monochromatic nonbreaking waves

Field observations often show a considerable variation in mean grain size along the coastal profile. Under high waves in shallow water, bed ripples are washed out, and sheet flow becomes the dominant transport mode: large amounts of sand are transported in a thin layer close to the bed, i.e., the sheet flow layer. This paper focuses on grain size influences on transport processes in oscillatory sheet flow. Experiments were carried out in the Large Oscillating Water Tunnel (LOWT) of Delft Hydraulics, in which near-bed orbital velocities in combination with a net current can be simulated at full scale. Three uniform sands with different mean grain size were used. It was found that in contradiction to expressions found in literature, both the erosion depth and the sheet flow layer thickness are larger for fine sand (D 50 = 0.13 mm) than for coarser sand (D 50 ≥ 0.21 mm). Measured time-averaged velocity and concentration profiles indicate that the presence of a sheet flow layer leads to an increased flow resistance and to damping of turbulence and that these effects are stronger for a thicker sheet flow layer (i.e., for fine sand). These mobile-bed effects are analyzed further by comparing the measurements with the results of a one-dimensional vertical advection-diffusion boundary layer model. Simulating the mobile-bed effects in the model by introducing an increased roughness height and a reduced turbulent eddy viscosity showed that the roughness height is of the order of the sheet flow layer thickness and that turbulence damping increases for a decreasing grain size.

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Mobile-bed effects in oscillatory sheet flow

On the basis of the Wilcox [1992] transitional k-ω turbulence model, we propose a new k-ω turbulence model for one-dimension vertical (1DV) oscillating bottom boundary layer in which a separation condition under a strong, adverse pressure gradient has been introduced and the diffusion and transition constants have been modified. This new turbulence model agrees better than the Wilcox original model with both a direct numerical simulation (DNS) of a pure oscillatory flow over a smooth bottom in the intermittently turbulent regime and with experimental data from Jensen et al. [1989] , who attained the fully turbulent regime for pure oscillatory flows. The new turbulence model is also found to agree better than the original one with experimental data of an oscillatory flow with current over a rough bottom by Dohmen-Janssen [1999] . In particular, the proposed model reproduces the secondary humps in the Reynolds stresses during the decelerating part of the wave cycle and the vertical phase lagging of the Reynolds stresses, two shortcomings of all previous modeling attempts. In addition, the model predicts suspension ejection events in the decelerating part of the wave cycle when it is coupled with a sediment concentration equation. Concentration measurements in the sheet flow layer give indication that these suspension ejection events do occur in practice.

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1DV bottom boundary layer modeling under combined wave and current: turbulent separation and phase lag effects

This paper presents an idealized morphodynamic model to predict river dune evolution. The flow field is solved in a vertical plane assuming hydrostatic pressure conditions. The sediment transport is computed using a Meyer-Peter–Muller type of equation, including gravitational bed slope effects and a critical bed shear stress. To avoid the necessity of modeling the complex flow inside the flow separation zone, we follow an approach similar to one used earlier to simulate the dynamics of wind-blown desert dunes. In case of flow separation, the separation streamline acts as an artificial bed and sediment avalanches down the leeside distributing evenly on the leeside at the angle of repose. Model results show that bed slope effects play a crucial role in the determination of the fastest-growing wavelength from a linear analysis. Flow separation is shown to be crucial to take into account if the dune lee exceeds a certain threshold slope. If flow separation is not included, dune shapes are incorrectly predicted and the dune height saturates at an early stage of bed form evolution, yielding an underprediction of dune height and time to equilibrium. The local bed slope at the dune crest plays a critical role for obtaining an equilibrium dune height. The simulation model is able to predict the main characteristics of dune evolution, such as dune asymmetry, dune growth, and saturation at a certain dune height. Dune dimensions, migration rates, and times to equilibrium compare reasonably well to various data sets.

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C. Marjolein Dohmen-Janssen

Papers

Phase lags in oscillatory sheet flow: experiments and bed load modelling

Sheet flow dynamics under monochromatic nonbreaking waves

Mobile-bed effects in oscillatory sheet flow

1DV bottom boundary layer modeling under combined wave and current: turbulent separation and phase lag effects

Modeling river dune evolution using a parameterization of flow separation