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Introduction
Published in Bujang B. K. Huat, Arun Prasad, Sina Kazemian, Vivi Anggraini, Ground Improvement Techniques, 2019
Bujang B. K. Huat, Arun Prasad, Sina Kazemian, Vivi Anggraini
Sand dunes move forced by wind through different mechanisms. They can move through a mechanism known as saltation, where the particles of sand are removed from the surface and are carried by the wind before landing back on the surface. When these particles land, they can scatter other particles and cause them to move as well. Another mechanism is present on the steep slopes of the dunes, where the sand is falling down: this is the “sand avalanche”. Therefore, if we are on the sloping windward side, we can see the sand grains that jump a few centimeters above the surface of the dune. At the dune’s crest, the airborne sand grains fall down the steep slope as small avalanches. With strong winds, the sand particles move in a sheet flow. This is an overland motion of the sand having the form of a continuous layer over the soil. The mass transferred by this flow is extremely large. Then, during a strong dust storm, the dunes may move more than several meters (Figure 1.14). A map showing sand dunes in the Arabian peninsula is shown in Figure 1.15. Sand dunes affect many infrastructures and cause delays in construction.
Conceptual and detailed design
Published in Dominic Reeve, Andrew Chadwick, Christopher Fleming, Coastal Engineering, 2018
Dominic Reeve, Andrew Chadwick, Christopher Fleming
The formation of sand dunes is dependent upon two main factors. The first is an abundant supply of sand-sized sediment and the second a strong onshore wind to enable entrainment and transportation of sand from the beach to the dunes. Backshore dune development can be facilitated by a low gradient sandy beach, which provides a large expanse of beach sand exposed at low tide. Whilst establishment of colonising vegetation can influence dune morphology, it is not essential for their formation (Pye and Tsoar 1990). Dunes can move through migration that occurs through a mechanism of wind driven saltation of the sand grains resulting in erosion of the front (exposed) face and deposition on the back (sheltered) face. It follows that any such movement is in the same direction as the prevailing wind. There are examples where sand dune migration has been part of a natural mechanism for transferring sand from one beach to another across a headland. As a general rule sand dune mobility is controlled by the rate of sand supply, the magnitude and frequency of wind, and vegetation cover (Pye 1983). The marine erosion of dunes is more complex than that of cliffs because of the close interaction between the beach and the dune. The outcome of this is that dunes can both accrete and retreat. Erosion rates of dunes can be very high and rapid because they are composed of unconsolidated sands. The type of dune failure varies due to exposure, dune morphology and vegetation cover (Carter and Stone 1989).
Air pollutants
Published in Abhishek Tiwary, Jeremy Colls, Air Pollution, 2017
It may not be obvious how a wind flowing parallel to the surface can generate a lifting force. One common mechanism is saltation (from the Latin for jump or leap). Once particles such as sand grains have been set in motion, they strike other grains on the surface. Sometimes they will bounce up into the air flow after such a collision. The particles’ relaxation time is comparable to the time they take to return to the surface at their sedimentation speed, so that they accelerate to the wind speed at that height (which might be several m s–1 only a few cm above the surface). This gives them momentum for the next collision, and so on. Theory and experiment show that the rate of saltation depends on the cube of the wind speed. Saltating grains will usually be in the 50–300 μm diameter range, moving amongst larger grains, which either remain stationary or roll along, and amongst smaller ones. When the smaller ones are ejected by the saltating grains, they become airborne and leave the area, possibly to form loess soils or red rain or ocean sediment thousands of km downwind. In addition, the sand blasting effect of the windborne grains on larger rocks can create a new supply of smaller grains for removal. Although the saltation process is most easily visualised for a dry sand region such as a desert or beach, it will contribute to soil erosion for all soils, depending on the fetch upwind, the size distribution of the soil particles, the moisture content and the extent of vegetation.
Identification and quantification of erosion on a sand tailings dam
Published in Geosystem Engineering, 2020
N. Slingerland, A. Sommerville, D. O’Leary, N.A. Beier
Wind erosion was noted in the field, particularly on the upper portions of the dams. Figure 8(a) shows light-coloured wind-blown CST with an area of deflation in the background and wind ripples clearly visible in the foreground. A 0.3-m long trowel has been placed adjacent to the wind ripples in Figure 8(b) to provide scale. These wind ripples are formed by saltation: a chain reaction process by which a sand grain mobilized by wind collides with other sand or silt-sized particles, displacing them into the air and continuing the process when they land on other sand grains (Sauer & Elder, 1986). Silt tends to be suspended in the turbulent air more easily than sand due to its small grain size, and this was evident on site with significant blowing sediment at heights greater than 1.8 m above grade.
LES-DEM simulations of sediment saltation in a rough-wall turbulent boundary layer
Published in Journal of Hydraulic Research, 2019
Detian Liu, Xiaofeng Liu, Xudong Fu
The understanding of saltation process is the key to quantify how sediment moves as bedload because saltation is the major mode of particle motion (Lee, You, & Lin, 2002). Despite decades of research, the dynamics of bedload particle saltation are still not fully understood. This paper presents new findings from a study using a three-dimensional (3D) model coupling large eddy simulation (LES) with a discrete element model (DEM). The central scientific question in this work is how to quantify the effects of turbulence and bed collision, both of stochastic nature, on saltation velocity, trajectory, and dispersion.
Numerical investigation of snow accumulation on a high-speed train by snow saltation
Published in International Journal of Rail Transportation, 2023
Jinkyu Bae, Soonho Shon, Hyeokbin Kwon, Kwanjung Yee
Figure 1 depicts the three types of particle transport by the wind [40]. First, the particles roll or slide in contact with the ground at low fluid velocities, which is called surface creep. When the wind reaches a certain critical velocity, stationary or creeping particles leap into the air, which is referred to as saltation. Suspension, which is the third type, generally affects smaller and lighter particulates with diameters less than 70 μm [41]. The particulates are negligibly influenced by gravity; therefore, they stay longer in the air.