Mechanics of Wind-blown Sand Movements

Mechanics of Wind-blown Sand Movements
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Single and double straight fence rows are the most commonly used. Fences are often built to accomplish a specific primary purpose, but they can cause many different and often unanticipated changes to the landscape. The effects of a sand fence change through time as the initial structure traps sand , creates a dune that is colonized by vegetation, and becomes integrated into the environment by increasing topographic variability and aesthetic and habitat value. Sand fences can be made more compatible with natural processes by not placing them in locations where sources of wind blown sand are restricted or in unnatural shore perpendicular orientations.

Symbolic fences are less expensive, are easy to replace when damaged, are less visually intrusive, and can be used for controlling pedestrian access. Movements of water, solutes, and stable isotopes in the unsaturated zones of two sand plains in the upper Midwest.

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Yuan, et al. J Coast Res, p. Password Changed Successfully Your password has been changed. Winds that blow from the SW to SE quadrant strongly affect the backshore morphology, normally eroding this zone. The scope of this Along similar lines, when simulating complex phenomena, there are often aspects which appear to be essentially random.

Four month-long field experiments investigated movements of water and solutes through unsaturated sand plains near Princeton, Minnesota, and Oakes, North Dakota. Atrazine and bromide were applied to bare soils and soils planted with corn. The field plots were irrigated according to local farming practices.

Theoretical Simulation of Developing Process of Wind-Blown Sand Movement

At the end of each experiment, unsaturated soils were analyzed for atrazine and bromide concentrations and oxygen and hydrogen isotope compositions of soil water. Most soil water was affected by evaporation but groundwater beneath the plots had no evaporative isotopic signature. Therefore most recharge consisted of water that was unaffected by evaporation.

Sources of such water may have included snowmelt, prolonged or high-intensity rainfalls that were not interrupted by periods of drying, and water that moved through preferential flow paths. Preferential flow also was suggested by the detection of atrazine, deethylatrazine, and bromide in groundwater shortly after each application of irrigation water at Princeton and by isolated concentrations of atrazine and bromide in soil well below the main masses of chemicals at Oakes. Movement of tagged dredged sand at thalweg disposal sites in the Upper Mississippi River.

get link Volume 2. Savanna Bay and Duck Creek sites. Experiments were conducted on the Upper Mississippi River at two sites, Savanna Bay and Duck Creek, to investigate the movement of dredged sand after disposal in the thalweg. These experiments are part of a larger study, which includes similar experiments conducted earlier at two other sites on the Upper Mississippi River. At the Savanna Bay site, hydraulically dredged sand was tagged with sand coated with fluorescent dye before being deposited as a pile in the thalweg.

At the Duck Creek site, only bathymetric surveys were conducted. The general behavior of the disposal piles at these two new sites was similar to that of the piles at the first two sites. Topographic evidence of the piles disappeared, and bottom conditions similar to the predisposal conditions were reestablished following the first period of high river flows after disposal.

At Savanna Bay, as had happened at the first two sites, the tagged sand remained in the main river channel as it moved downstream in response to flood currents and did not migrate into nearby border areas, backwaters, or sloughs. Hussain, M. Particulate air pollution is a problem of health concern. The microscopic make-up of different varieties of sand particles found and collected at a sand dune site in Badr, Saudi Arabia has been determined.

Primary emphasis is given to the use of multiple high resolution electron microscopy viz. Silicates alumino-silicates and quartz clear, milky, rose dominate white sand and rest appears to contain calcite, olivine, feldspar, and magnetite.

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Black sand particles exhibit very different morphologies and microstructures surface roughness compared with white sand and volcanic ash. Morphological analyses have shown that the black sand contain ultrafine particles. Black sand is strongly magnetic, which indicates the mineral magnetite strongly magnetic or elemental iron. Natural and anthropogenic sources have been implicated for the observed particles.

Laboratory Tests on Engineering Properties of Wind-Blown Sand

Analysis revealed that the surface of white sand particles is mainly covered with the fine particles. It is known that emissions from combustion contain carbon soot and other contaminants that are easily absorbed by soil particles during a long-range transport. Wind-shield walls decrease the velocity of wind-drift sand flow in transit. This results in sand accumulating in the wind-shadow zone of both windshield wall and track line, causing severe sand sediment hazard. This study reveals the characteristics of sand accumulation and the laws of wind-blown sand removal in the wind-shadow areas of three different types of windshield walls, utilizing three-dimensional numerical simulations and wind tunnel experiments and on-site sand sediment tests.

The results revealed the formation of apparent vortex and acceleration zones on the leeward side of solid windshield walls. For uniform openings, the vortex area moved back and narrowed.

When bottom-opening windshield walls were adopted, the track-supporting layer at the step became a conflux acceleration zone, forming a low velocity vortex zone near the track line. At high wind speeds, windshield walls with bottom-openings achieved improved sand dredging.

Considering hydrodynamic mechanisms, the flow field structure on the leeward side of different types of windshield structures is a result of convergence and diffusion of fluids caused by an obstacle. This convergence and diffusion effect of air fluid is more apparent at high wind velocities, but not obvious at low wind velocities. This document summarizes 20 articles and books which stress the importance of movement in the overall development of the human species.

Each summary ranges in length from to words and often includes direct quotations. A wide range of movement activities suitable for people of all ages from infants to adults are discussed. Many summaries…. A continuously weighing, high frequency sand trap: Wind tunnel and field evaluations. A new continuously weighing, high frequency sand trap CWHF has been designed.

Its sampling efficiency is evaluated in a wind tunnel and the potential of the new trap has been demonstrated in field trials.

The newly designed sand trap allows fully automated and high frequency measurement of sediment fluxes over extensive periods. We show that it can capture the variations and structures of wind-driven sand transport processes and horizontal sediment flux, and reveal the relationships between sand transport and meteorological parameters.

Its maximum sampling frequency can reach 10 Hz. Wind tunnel tests indicated that the sampling efficiency of the CWHF sand trap varies between It achieved a maximum sampling efficiency of This is largely achieved by the inclusion of a vent hole which leads to a higher sampling efficiency than that of a step-like sand trap at high wind speeds.

In field experiments, we show a good agreement between the mass of sediment from the CWHF sand trap, the wind speed at 2 m and the number of saltating particles at 5 cm above the ground surface. According to analysis of the horizontal sediment flux at four heights from the CWHF sand trap 25, 35, 50, and cm , the vertical distribution of the horizontal sediment flux up to a height of cm above the sand surface follows an exponential function. Our field experiments show that the new instrument can capture more detailed information on sediment transport with much reduced labor requirement.

Therefore, it has great potential for application in wind-blown sand monitoring and process studies. Large-scale natural gradient tracer test in sand and gravel, Cape Cod, Massachusetts: 1. Experimental design and observed tracer movement.

Mechanics, Materials Science & Engineering Journal

LeBlanc, Denis R. A large-scale natural gradient tracer experiment was conducted on Cape Cod, Massachusetts, to examine the transport and dispersion of solutes in a sand and gravel aquifer. The nonreactive tracer, bromide, and the reactive tracers, lithium and molybdate, were injected as a pulse in July and monitored in three dimensions as they moved as far as m down-gradient through an array of multilevel samplers. The bromide cloud moved horizontally at a rate of 0.

It also moved downward about 4 m because of density-induced sinking early in the test and accretion of areal recharge from precipitation. After m of transport, the bromide cloud had spread more than 80 m in the direction of flow, but was only 14 m wide and 4—6 m thick. Influence of detergent formulation on nutrient movement through sand columns simulating mound and conventional septic system drainfields.

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The effects of phosphate P and zeolite Z -built detergents on leaching of N and P through sand columns simulating septic system drainfields were examined in laboratory columns. To simulate mound septic system drainfields, paired sets of columns were dosed intermittently with septic tank effluent from households using P- or Z-built detergent.

Two other paired sets of columns were flooded with P- or Z-effluent to simulate new conventional septic system drainfields; after clogging mats or "crusts" developed at infiltration surface, the subsurfaces of the columns were aerated to simulate mature crusted conventional septic system drainfields. NO 3 loading in leachate was 1. Dosed columns removed P poorly; total phosphorus TP loading in leachate was 81 and 19 g m -2 yr -1 with P- and Z-effluent, respectively.

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In flooded columns 1. Flooded columns removed P efficiently; TP leached through flooded systems was 2. Crusted columns fed Z-effluent leached 1. Crusted columns removed P satisfactorily: 8. The P-built detergent substantially improves the efficiency of N removal with satisfactory P removal in columns simulating conventional septic system drainfield.

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Simultaneous removal of N and P under flooded conditions might be explained by precipitation of struvite-type minerals. Dosed system drainfields were less efficient in removing N and P compared to flooded and crusted system drainfelds. Greiner, J. We discover a break in the afterglow light curve after 1. The jet origin of this break is supported by the fact that the spectral energy distribution is achromatic during the first four days. During later phases, GRB shows significant excess emission above the flux predicted by a power law, which we interpret as additional light from an underlying supernova.

In particular, the spectral energy distribution of the optical transient approximately 2 weeks after the burst is clearly not of power-law type, but can be presented by a black body with a temperature of approx. The deduced parameters for the decay slope as well as the spectral index favor a wind scenario, i. Saltation of Non-Spherical Sand Particles. Saltation is an important geological process and the primary source of atmospheric mineral dust aerosols.

Unfortunately, no studies to date have been able to precisely reproduce the saltation process because of the simplified theoretical models used. For example, sand particles in most of the existing wind sand movement models are considered to be spherical, the effects of the sand shape on the structure of the wind sand flow are rarely studied, and the effect of mid-air collision is usually neglected.