Estimation of Sand Transportation Rate for Fixed and Semi-Fixed Dunes Using Meteorological Wind Data

Taibus County, Inner Mongolia, China, lies in a farming-pastoral ecotone, where severe wind erosion and various aeolian sand hazards are prevalent and fixed and semi-fixed sand dunes occur frequently. This study was conducted to investigate the relationships between sand transportation rate and wind speed for the fixed and semi-fixed sand dunes based on field measurements. The annual quantity of soil erosion by wind was estimated using meteorological wind data. The results indicated that the sand transportation rate in Taibus County in 2000 was 57.38 kg cm-1 year-1 for the semi-fixed dunes and 4.56 kg cm-1 year-1 for the fixed dunes. The total duration of erosive winds covered 12.5% of the time of the year, and spring posed the highest potential of sand transportation. Wind with low speed (≤ 17 m s-1) and high frequency plays a dominant role in sand transportation, while strong wind (≥ 17 m s-1) with low frequency significantly enhanced the sand transportation. Erosive wind speed, directions, and frequency were three crucial dynamic factors influencing sand hazards in the farming-pastoral ecotone. The dominant factors intensifying sand and dust storms in Taibus County might be related to the favorable wind condition in combination with the durable drought, which led to land desertification and vegetation degradation.

Field Measurements of Influence of Sand Transport Rate on Structure of Wind-sand Flow over Coastal Transverse Ridge

The structure of wind-sand flow under different total sand transport rates was measured with field vertical anemometer and sand trap on the crest of typical coastal transverse ridge in Changli Gold Coast of Hebei Province, which is one of the most typical coastal aeolian distribution regions in China and famous for the tall and typical coastal transverse ridges. The measurement results show that, on the conditions of approximate wind velocities and same surface materials and environments, some changes happen to the structure of wind-sand flow with the increase of total sand transport rate on the crest of coastal transverse ridge. First, the sand transport rates of layers at different heights in the wind-sand flow increase, with the maximum increase at the height layer of 4-8cm. Second, the ratios of sand trans-port rates of layers at different heights to total sand transport rate decrease at the low height layer (0-4cm), but increase at the high height layer (4-60cm). Third, the distribution of the sand transport rate in the wind-sand flow can be expressed by an exponential function at the height layer of 0-40cm, but it changes from power function model to ex-ponential function model in the whole height layer (0-60cm) and changes into polynomial function model at the height layer of 40-60cm with the increase of total sand transport rate. Those changes have a close relationship with the limit of sand grain size of wind flow transporting and composition of sand grain size in the wind-sand flow.

Effect of Energy Density and Gas Velocity on Transport Rate of Ions

In order to study the effect of the parameters such as the energy density and the gas velocity on the transport rate of ions, the applied force and the motion law of charged particles in the electric field of corona discharges at atmospheric pressure is investigated in this paper. As a result, when the gas velocity is raised from 1.5 m/s to 25 m/s for an energy density of 0.4 mJ/cmz, the ionic transport rate increases from 5.4 × 10^8/cm^3. s to 8× 10^10/cm^3 .s, which is an increase of over two orders of magnitude. However, in the zones of streamer and glow discharges, the effect of the input energy density and the energy density of gas ionization on the transport rate is below one order of magnitude. In conclusion, the increase of charged particle momentum can be a major factor in raising the transport rate and reducing the volume of the plasma sources.

Effect of upward seepage on bedload transport rate

The paper presents an investigation of injection effects on the bedload transport rate. According to dimensional analysis, two dimensionless groups, an Einstein＇s parameter group and a modified densimetric Froude number group, were chosen to examine how injection affects the bedload transport rate. Experimental studies were conducted in an open-channel flume with an upward seepage zone. The sediment particles used for the test were 0.9 mm in diameter. The experimental results show that an increase in the injection velocity causes a reduction in the shear velocity excess, which is defined as the difference between the shear and critical shear velocities, leading to a reduction in the bedload transport rate. The equation for predicting the bedload transport rate in the presence of upward seepage was derived empirically. The proposed prediction method is suitable for engineering practice, since it only requires the undisturbed flow condition, properties of sediment particles, and the injection velocity.

Nonlinear Analysis of Bedload Transport Rate of Paroxysm Debris Flow

The evolution characteristics of bedload transport feature of paroxysm debris flow have been studied by means of both theory analysis and experimental data.The analysis based on the flume experiment data of a sand pile model as well as a large amount of field data of debris flow clearly shown that the statistical distribu- tion for the main variable of the sand pile made of non-uniform sand (according the sand pile experiment,φ≥2.55) conform to the negative power law,that means the non-uniform sand syste...

Bed Load Transport Rate in Scouring and Armoring Process of Non-uniform Sediment River Bed

Flume experiments were carried out to study bed load transport rate during rive bed scouring and ar- moring.A theoretical differential equation linking the transport rate to the probability of incipient motion of non-uniform sediment is solved.The transport rate is shown to decrease exponentially with time,according to the theory,which is in good agreement with the experiment data.

Thermodynamic Effects on Particle Movement:Wind Tunnel Simulation Results

Sand/dust storms are some of the main hazards in arid and semi-arid zones. These storms also influence global environmental changes. By field observations, empirical statistics, and numerical simulations, pioneer researchers on these natural events have concluded the existence of a positive relationship between thermodynamic effects and sand/dust storms. Thermodynamic effects induce an unsteady stratified atmosphere to influence the process of these storms. However, studies on the relationship of thermodynamic effects with particles (i.e., sand and dust) are limited. In this article, wind tunnel with heating was used to simulate the quantitative relationship between thermodynamic effects and particle movement on different surfaces. Compared with the cold state, the threshold wind velocity of particles is found to be significantly decrease under the hot state. The largest decrease percentage exceedes 9% on fine and coarse sand surfaces. The wind velocity also has a three-power function in the sand transport rate under the hot state with increased sand transport. Thermodynamic effects are stronger on loose surfaces and fine particles, but weaker on compacted surfaces and coarse particles.

A Three-Dimensional Model of Transport and Diffusion of Seeding Agents within Stratus

It is essential to learn the temporal and spatial concentration distributions and variations of seeding agents in cloud seeding of precipitation enhancement. A three-dimensional puff trajectory model incorporating a mesoscale nonhydrostatic model has been formulated, and is applied to simulating the transporting and diffusive characteristics of multiple line sources of seeding agents within super-cooled stratus. Several important factors are taken into consideration that affect the diffusion of seeding materials such as effects of topography and vertical wind shear, temporal and spatial variation of seeding parameters and wet deposition. The particles of seeding agents are assumed to be almost inert, they have no interaction with the particles of the cloud or precipitation except that they are washed out by precipitation. The model validity is demonstrated by the analyses and comparisons of model results, and checked by the sensitivity experiments of diffusive coefficients and atmospheric stratification. The advantage of this model includes not only its exact reflection of heterogeneity and unsteadiness of background fields, but also its good simulation of transport and diffusion of multiple line sources. The horizontal diffusion rate and the horizontal transport distance have been proposed that they usually were difficult to obtain in other models. In this simulation the horizontal diffusion rate is 0.82 m s(-1) for average of one hour, and the horizontal average transport distance reaches 65 km after 1 4 which are closely related to the background Fields.

Experimental study on bed-load sediment transport under irregular wave and current combined flow

Using an irregularly oscillating tray and flume, a series of experiments are completed to evaluate bed-load sediment transport rate under irregular wave -current coexistent field. Testing conditions include three interaction angles 0', 45', 90' and two kinds of median sizes (0.38 and 1.10 mm). The results of transport rate show that the net sediment transport rate can be expressed approximately as the function of the maximum bottom shear stress of waves, mean shear stress of current and the grain size.

Quantifying key model parameters for wheat leaf gas exchange under different environmental conditions

The maximum carboxylation rate of Rubisco(Vcmax)and maximum rate of electron transport(Jmax)for the biochemical photosynthetic model,and the slope(m)of the Ball-Berry stomatal conductance model influence gas exchange estimates between plants and the atmosphere.However,there is limited data on the variation of these three parameters for annual crops under different environmental conditions.Gas exchange measurements of light and CO2 response curves on leaves of winter wheat and spring wheat were conducted during the wheat growing season under different environmental conditions.There were no significant differences for Vcmax,Jmax or m between the two wheat types.The seasonal variation of Vcmax,Jmax and m for spring wheat was not pronounced,except a rapid decrease for Vcmax and Jmax at the end of growing season.Vcmax and Jmax show no significant changes during soil drying until light saturated stomatal conductance(gssat)was smaller than 0.15 mol m^–2 s^–1.Meanwhile,there was a significant difference in m during two different water supply conditions separated by gssat at 0.15 mol m^–2 s^–1.Furthermore,the misestimation of Vcmax and Jmax had great impacts on the net photosynthesis rate simulation,whereas,the underestimation of m resulted in underestimated stomatal conductance and transpiration rate and an overestimation of water use efficiency.Our work demonstrates that the impact of severe environmental conditions and specific growing stages on the variation of key model parameters should be taken into account for simulating gas exchange between plants and the atmosphere.Meanwhile,modification of m and Vcmax(and Jmax)successively based on water stress severity might be adopted to simulate gas exchange between plants and the atmosphere under drought.

Sediment generation and soil mound denudation in areas of high-density tree throw along a river valley in the Jura Mountains, Switzerland

A preliminary field-based investigation was undertaken in a small(<10 km^(2))river valley located in the mountainous Jura region of northwest Switzerland.The aims of the work were to assess sediment generation and annual sediment transport rates by tree throw on forested hillslopes,and to document surface hydrology characteristics on four fresh soil mounds associated with recent tree throws over a 24-day monitoring period.For the soil mounds,average sediment recovery ranged from 7.7-28.2 g(dry weight),equivalent to a suspended sediment concentration of 145.2-327.8 g L^(-1),and runoff coefficients ranged from 1.0%-4.2%.Based on a soil bulk density value of 1,044 kg m^(-3),upslope runoff generation areas were denuded by an average 0.14 mm by the end of the 24-day monitoring period,representing an erosion rate equivalent to 2.1 mm yr^(-1).A ca.50 cm high soil mound could therefore feasibly persist for around 200-250 years.For tree throw work,the dimensions of 215 individual tree throws were measured and their locations mapped in 12 separate locations along the river valley representing a cumulative area equivalent to 5.3 ha(av.density,43 per ha).Tree throws generated a total of 20.1 m^(3) of fine-sediment(<2 mm diameter),or the equivalent of 3.8×10^(-4) m^(3) m^(-2).The process of tree throw was originally attributed to two extreme weather events that occurred in west and central Europe in late December 1999.Taking the 18-year period since both storms,this represents an annual sediment transport rate of 2.7×10^(-5) m^(3) m^(-1) yr^(-1).Exploring the relationship with wind on fall direction,65.5%of tree throws(143)generally fell in a downslope direction irrespective of hillslope aspect on which they were located.This infers that individual storms may not have been responsible for the majority of tree throws,but instead,could be associated with root failure.Given the high density of tree throws and their relative maturity(average age 41 years),we hypothesise that once trees attain a certain age in this river valley,their physiognomy(i.e.height,mass and centre of gravity)compromises their ability to remain securely anchored.We tentatively attribute this possibility to the presence of bedrock close to the surface,and to the shallow soil profile overlaying steep hillslopes.

Effect of thermal diffusion and electrostatic force on evolution of wind-blown sand flow

A theoretical model is suggested to mathematically describe the effect of thermal diffusion from a sand-bed on evolution of a wind-blown sand flow. An upward wind field is engendered by the thermal diffusion and the coupling interaction among the horizontal and upward wind flow, saltating grains, and a kind of electrostatic force exerted on the grains are considered in this theoretical model. The numerical results show that the effect of the thermal diffusion on the evolution process of wind-blown groan flow is quite obvious and very similar to the effect of the electrostatic force on the evolution. Not only the time for the entire system to reach a steady state （called the duration time）, the transport rate of grains, the mass-flux profiles and the trajectory of saltating grains are affected by the thermal diffusion and the electrostatic force exerted on saltating grains, but also the wind profiles and the temperature profiles at the steady state are affected by the wind-blown sand flow.

An Investigation of Stochastic Nature of Bed Load Motion in Chuanjiang River

Bed Load Motion and its transport rate is one of the basic issues in river dynamics.In this paper, the authors discussed the stochastic nature of bed load motion in Chuanjiang River in details.Chungjiang lies in the upstream reach of Yangtze River.Its stochastic nature is shown in the following four aspects.Firstly, even though all the conditions are the same,due to the fluctuation of the flow,the bed load discharge and the location and width of sediment transport belts are different.Secondly,during the ...

Time-Dependent Sediment Transport Subjected to Downward Seepage

Experiments were conducted using cohesionless sand particles with median diameter of 0.48 mm to investigate the time variation of sediment transport rate under the influence of local downward seepage.The experimental results show that the bedload transport rate in terms of volumetric sediment transport rate per unit width increased rapidly with time in the presence of suction,eventually reaching a peak beyond which it started to decrease.The trend of reduction was significantly reduced beyond 8 400 s after the test started.The analytical expression was derived in terms of dimensionless sediment transport rate and dimensionless time.The hypothesized relationships were compared with the experimental data,indicating a good agreement with each other.

Incipient Velocity of Non-uniform Sediment in Sloping River Bends

A model for incipient movement of sediment in rolling pattern was established. In this model, the starting of sediment particles under low transport rate, the exposure degree of sediment, the lateral slope of water surface and the effect of transverse circulating current induced by the hydraulic structure of bend flow were fully considered. A theoretical formula for the incipient velocity of non-cohesive and non-uniform sediment in sloping river bends was developed. The results from the theoretical formula compared well with the experimental data.

Comparative Analysis of the Erosion Mechanism of Different Profiles in the Arcuate Foreshore under Typhoon Action

The comparison results of three beach profile data repeatedly measured before and after the typhoon in Shuidong Bay,west Guangdong province which show that there are significant differences in beach profile erosion and response process.And the changes of beach profile can be divided into:strong downward overall low shoreline regressive type and overall slight erosion shoreline regressive type.Application of the modified mildslope equation along three beach profile are simulated wave high reflection to the sea side,to the section vertical shore pressure gradient and including water roll force and radiation stress,the vertical shore forces one dimensional profile along the momentum conservation equation(radiation stress and water roll force)bottom friction and lateral mixing reaction between numerical solution,the momentum conservation equations of the wave increases the water flow velocity and section along the profile distribution of wave height and related forces.The analysis shows that the extent and difference of coastal erosion depend on the shoreline erosion mode stimulated by the maximum surge water of the coastal current and the maximum velocity of the coastal current and the dynamic state of the profile topography under the action of the profile location,morphology and incident wave elements.

Sediment control function of river notches

The purpose of this study is to investigate the control function and mechanisms of natural river notches. Physical and numerical experiments are analyzed in this study for two representative types of sediment events： high intensity and short duration Type A sediment disaster events, and low intensity and long duration Type B moderate non-disaster events. Two dimensionless parameters, sediment trapping rate and reduction rate of peak sediment transport, are defined to evaluate the sediment control function of river notches. Study results indicate that the contraction ratio of the notch has a significant influence on sediment control function, with high contraction ratios resulting in both high sediment-trapping and high reduction rates. River notches provide better sediment control during Type A events than Type B events. The sediment control mechanism of river notches is the result of multiple interactions among river flow, sediment transport, and riverbed variation. Analysis of these interactions supports the significant protection role of river notches on sediment control for disaster events.

Development of All-Weather and Real-Time Bottom-Mounted Monitor of Bed Load Quantity

Quantity of bed load is an important physical parameter in sediment transport research. Aiming at the difficulties in the bed load measurement, this paper develops a bottom-mounted monitor to measure the bed load transport rate by adopting the sedimentation pit method and resolving such key problems as weighing and desilting, which can achieve long-time, all-weather and real-time telemeasurement of the bed load transport rate of plain rivers, estuaries and coasts. Both laboratory and field tests show that this monitor is reasonable in design, stable in properties and convenient in measurement, and it can be used to monitor the bed load transport rate in practical projects.

室内模拟戈壁地表降雨对风蚀过程的影响

In the present study,indoor experiments were carried out to investigate the effects of rainfall on subsequent wind erosion processes on the simulated Gobi surface,with soils and gravels collected from the Alax Gobi in northwestern China.The results showed that the wind erosion rate(WR)ranged from 0.4 to 1931.2 g m^((-2)min^((-1)and that the sediment transportation rate(STR)ranged from 0.00 to 51.47 g m^((-2)s^((-1)under different gravel coverage conditions(0%,20%,40%and 60%)when the wind velocity changed from 6 m s^((-1)to 18 m s^((-1).Both WR and STR increased with increasing wind velocity as a power function and decreased with increasing gravel coverage.The rainfall event had significant inhibitory effects on WR and STR,and the complex effects of soil crust formation and the changing soil surface roughness(SSR)by rainfall event played significant roles in reducing these rates during subsequent wind erosion.In this study,a valuable exploration of the effects of rainfall events on subsequent wind erosion processes in the Gobi area was conducted.The findings are of great significance for a better understanding and effective prediction of dust emissions in this region.

Regulating ion transport behaviors toward dendrite-free potassium metal batteries:recent advances and perspectives

With abundant potassium resources and high capacity,potassium metal batteries(PMBs)present a compelling option for the next generation of energy storage technology.However,PMBs suffer from an unstable anode interface caused by uncontrolled dendrite growth,which results in unsatisfactory cyclability and safety concerns.Extensive investigations suggest that significant progress has been made in enhancing the interfacial stability of PMBs.The various effective strategies for stabilizing interfaces can ultimately be attributed to the regulation of the sluggish ion transfer kinetics and irregular deposition,i.e.,the arrangement of ion transport behaviors at the interface.Rational modulation of ions transport rate and ions deposition directions makes it possible to obtain a dendrite-free and smooth deposition plane.Herein,the influencing factors and action mechanism of K^(+)interface transport behaviors are discussed to understand the nature of material design for constructing stable anode interfaces,including regulating the solvation and desolvation structures,accelerating K^(+)transport kinetics and controlling K^(+)deposition direction.In addition,the deficiencies and prospects of the research on electrolyte,separators and designed electrode involved in the manufacturing and testing and ion transport process of PMBs are discussed.This review is expected to provide some possible directions for constructing dendrite-free interfaces in advanced PMBs-related research and offer significant insights for prospective experimental research and commercial applications.