Threshold Wind Velocity Research Articles

Characteristics of the Aeolian Sediments Transported Above a Gobi Surface

AbstractGobi’s (gravel deserts) are one of the largest dust sources in northern China. Previous studies indicated that sand transport processes above the surface differed between Gobi and sand surfaces. However, the sand transport rate and related dust emission processes above Gobi (gravel) surfaces are still poorly understood. In this field study, we quantified this transport to provide important support for parameterizing Aeolian sediment transport models and clarifying the relationship between dust emission and transport. Threshold wind velocity can reach 0.38 ± 0.04 (mean ± SD) m s−1 above Gobi surfaces. Compared to the most commonly used sand‐transport models, we found that the Lettau and Lettau sediment transport model can be used to calculate horizontal sediment transport above a Gobi surface. The relationship between the vertical sediment transport (Fs) and shear velocity could be expressed using a power function. Although the horizontal sand transport and vertical flux (Q and Fs, respectively) above Gobi surfaces can be expressed similarly to previous results (i.e., using similar equation forms), the equation coefficients were much larger for the Gobi surface than for a shifting sand surface; that is, sediment transport was higher above the Gobi surface. This difference resulted from the larger sand transport rate and saltation height above the Gobi surface, and the larger transport and higher saltation height were related to the larger sand transport height and higher content of coarse sand transported above the Gobi surface.

Thermal Creep on Mars: Visualizing a Soil Layer under Tension

At low ambient pressure, temperature gradients in porous soil lead to a gas flow called thermal creep. In this regard, Mars is unique as the conditions for thermal creep to occur in natural soil only exist on this planet in the solar system. Known as a Knudsen compressor, thermal creep induces pressure variations. In the case of Mars, there might be a pressure maximum below the very top dust particle layers of the soil, which would support particle lift and might decrease threshold wind velocities necessary to trigger saltation or reduce angles of repose on certain slopes. In laboratory experiments, we applied diffusing wave spectroscopy (DWS) to trace minute motions of grains on the nanometer scale in an illuminated simulated soil. This way, DWS visualizes pressure variations. We observe a minimum of motion, which we attribute to the pressure maximum ∼2 mm below the surface. The motion above but especially below that depth characteristically depends on the ambient pressure with a peak at an ambient pressure of about 3 mbar for our sample. This is consistent with earlier work on the ejection of particle layers and is in agreement with a thermal creep origin. It underlines the supporting nature of thermal creep for particle lift, which might be especially important on Mars.

Calibração de parâmetros de simulação para a erosão eólica fluxo de gás sólido em duas fases em solos áridos e semiáridos

ABSTRACT To construct a coupled simulation model of soil wind erosion and two-phase flow in arid and semiarid regions, the proper contact parameters of the soil discrete element simulation model are obtained based on the angle of repose (AoR) calibration test. The coupled simulation model is established by combining computational fluid dynamics. The response value of the wind speed of sand initiation is used to verify the model’s accuracy. Due to the characteristics of arid and semiarid soils, this paper uses the Hertz-Mindlin with JKR contact model in EDEM software to calibrate the soil parameters based on soil physical tests and designs the Plackett-Burman, steepest climb, and Box-Behnken tests according to Design-Expert software to obtain the soil AoR second-order regression. With the AoR of 33.52° as the target, the best combination of parameters is obtained: soil-soil collision recovery of 0.64, soil-steel static friction coefficient of 0.31, JKR surface energy of 3.302 J m-2. Finally, by using calibrated parameters and the threshold wind velocity as the response value, the wind-sand air-solid two-phase flow test is conducted in ANSYS Fluent and EDEM, with the relative error between the starting wind speed recorded by the high-speed camera in the wind tunnel test and the threshold wind velocity shown in the simulation model calculated to be 8.7%, and the calibrated soil parameters met the requirements of the coupled simulation.

Microplastics in agricultural soils from a semi-arid region and their transport by wind erosion

Despite the importance of agricultural soils, little is known about the fate of microplastics (MPs) in this environment. In the present study, MPs have been determined in soils and wind-eroded sediments from two vegetable-growing fields in the Fars province of Iran, one using plastic mulch for water retention (Field 1) and the other using wastewater for irrigation (Field 2). MPs were heterogeneously distributed in the surface (0–5 cm) and subsurface (5–15 cm) soils of both fields, with a maximum concentration overall of about 1.1 MP g−1 and no significant differences in concentrations between either fields or depths. Fibres represented the principal shape of MPs, but spherules, presumably from wastewater, also made a significant (∼25%) contribution to MPs in Field 2. Analysis of selected samples by Raman spectroscopy and scanning electron microscopy revealed that polyethylene terephthalate (PET) and nylon were the most abundant polymers and that MPs exhibited varying degrees of weathering. Concentrations of MPs in this study are within the range reported previously for agricultural soils, although the absence of PET observed in earlier studies is attributed to the use of insufficiently dense solutions to isolate plastics. Deployment of a portable wind tunnel revealed threshold wind velocities for soil erosion of up to 7 and 12 m s−1 and MP erosion rates up to about 0.4 and 1.1 MP m−2 s−1 for Fields 1 and 2, respectively. Erosion rates are considerably greater than published depositional rates for MPs and suggest that agricultural soils act as both a temporary sink and dynamic secondary source of MPs that should be considered in risk assessments and global transport budgets.

Investigating threshold wind velocity for movement of sparsely distributed gravels in a wind tunnel: Effect of surface coarseness

In this study, wind tunnel experiments were conducted to determine the relationship between the texture of road surfaces and the threshold wind velocity that causes the movement of sparsely distributed gravels. We proposed a method that uses analogous particles having lower densities compared to actual gravel, considering the threshold velocity for gravel is too large to imitate in a typical wind tunnel. We first conducted a preliminary experiment, which confirmed that the threshold velocity for denser prototype particles can be estimated from the density ratios of the analogous and prototype particles. Furthermore, a main experiment was conducted to analyze different road surface textures using pumice stones, as their particle density is less than that of gravels. The results showed that coarser road surfaces exhibited larger threshold velocities for the gravel movement. Quantitatively, the coarsest asphalt concrete exhibited a threshold velocity that was 2.5 times larger than that of the smoothest surface (cement concrete). However, surface coarseness was dependent on the particle size, whereas the effect of particles trapped by the gaps in surfaces was more dominant than the fluid force acting on the particles of a relatively coarse surface. This force balance is reversed for a smooth surface, which indicates the possibility of determining threshold friction velocity from the particle size and surface texture coarseness.

Adaptive wind energy harvester with transformable bluff body

A novel adaptive wind energy harvester with a transformable bluff body responsive to external wind velocity is proposed in this study. This study is inspired by our finding that when an external wind velocity is lower than a specific (threshold) wind velocity, the energetic performance of an energy harvester with a certain cross-sectional shape of the bluff body is better than that with another shape and the reverse is true when the external wind speed is greater than the threshold. More specifically, the bluff body considered in the present study is composed of a prismatic cylinder and its cross-sectional shape is a triangle when the external wind velocity is below a certain threshold value. However, when the wind velocity exceeds the threshold value, the cross-sectional shape of the bluff body transforms into a W-shape in response to the wind velocity. In this study, an appropriate design process to develop the proposed system is established, and a physical prototype is fabricated. Thereafter, an associated mathematical model is developed and experimentally validated. The energetic and dynamic performances of the proposed system are thoroughly investigated and compared to systems with bluff bodies in three fixed cross-sectional shapes (square, triangle, and W-shape). As a result, the percentage increase ratio in the output power of the proposed energy harvester is found to be 23% higher than that of the system with a triangular bluff body, which is known to provide the best performance. This result indicates that the proposed system remarkably improves the energetic performance in comparison to the conventional system.

Radar measurements of blowing snow off a mountain ridge

Abstract. Modelling and forecasting wind-driven redistribution of snow in mountainous regions with its implications on avalanche danger, mountain hydrology or flood hazard is still a challenging task often lacking in essential details. Measurements of drifting and blowing snow for improving process understanding and model validation are typically limited to point measurements at meteorological stations, providing no information on the spatial variability of horizontal mass fluxes or even the vertically integrated mass flux. We present a promising application of a compact and low-cost radar system for measuring and characterizing larger-scale (hundreds of metres) snow redistribution processes, specifically blowing snow off a mountain ridge. These measurements provide valuable information of blowing snow velocities, frequency of occurrence, travel distances and turbulence characteristics. Three blowing snow events are investigated, two in the absence of precipitation and one with concurrent precipitation. Blowing snow velocities measured with the radar are validated by comparison against wind velocities measured with a 3D ultra-sonic anemometer. A minimal blowing snow travel distance of 60–120 m is reached 10–20 % of the time during a snow storm, depending on the strength of the storm event. The relative frequency of transport distances decreases exponentially above the minimal travel distance, with a maximum measured distance of 280 m. In a first-order approximation, the travel distance increases linearly with the wind velocity, allowing for an estimate of a threshold wind velocity for snow particle entrainment and transport of 7.5–8.8 m s−1, most likely depending on the prevailing snow cover properties. Turbulence statistics did not allow a conclusion to be drawn on whether low-level, low-turbulence jets or highly turbulent gusts are more effective in transporting blowing snow over longer distances, but highly turbulent flows are more likely to bring particles to greater heights and thus influence cloud processes. Drone-based photogrammetry measurements of the spatial snow height distribution revealed that increased snow accumulation in the lee of the ridge is the result of the measured local blowing snow conditions.

Wind Effect on the Size Distribution of Saltating Particles

Size distributions of saltating aleurite and sand particles have been measured in a windsand flux in a desertified area in Astrakhan oblast. The distributions are approximated by a sum of lognormal distributions for the aleurite-sand and aleurite fractions. The threshold wind velocity for the total particle concentration is determined under conditions of nonintermittent saltation. It is found that the threshold velocity depends on the size of saltating particles. Empirical approximations of the total number concentration and differential particle concentration of aleurite and sand particles as functions of wind velocity are obtained.

Hydrodynamic time parameters response to meteorological and physical forcings: toward a stagnation risk assessment device in coastal areas

Identifying zones of stagnation and deposition of terrigenous matter or contaminants induced by human activity is a key issue in coastal areas. In this paper, circulation processes and potential contaminant stagnation and deposition zones were assessed using hydrodynamic time parameters forced with meteorology. The study focused on an Eulerian time parameter, the local e-flushing time (eFT). The hydrodynamic modeling of coastal zones was applied to two bays of New Caledonia, located downstream of open mining sites. Numerous simulations were performed to classify the influence of forcing conditions on the eFT variability. The need to consider meteorological forcings rather than average weather conditions for the calculation of eFTs was demonstrated. In coastal zones, high wind velocity was the major forcing influencing eFTs, but below a threshold wind velocity, tidal range and river inputs became significant parameters. Spatial variations of eFT values, depending on meteorological conditions, induced varying risks of stagnation zones. General responses of the bays’ hydrodynamics and the exposure of zones to potential contaminants were defined under various forcings. Our findings demonstrate that strong turbulence zones are not always characterized by short eFTs because of antagonistic forcing effects. Diurnal tidal alternations were also proven to have less influence on eFT variations than tidal range changes over a lunar cycle.

An environmentally friendly soil improvement technology for sand and dust storms control

Background: Dust storms occur when unchecked, strong, or turbulent winds combine with exposed loose and dried soil surfaces. Sand and dust storms have a significant impact on society, economy, and environment at local, regional, and global levels. The environmental and health hazards of such storms cannot be permanently reduced, however, by taking appropriate measures, its impact can be reduced. The present study aimed to investigate the effects of microbial precipitation of calcium carbonate (CaCO3) as a biocompatible agent on soil stabilization and control of dust storms using ureaseproducing bacteria (UPB) as a biological improvement technique, which were isolated, identified, sprayed on the soil surface. Methods: For this purpose, the erosion of bio-cemented soil samples was investigated experimentally in a wind tunnel under the condition of wind velocity of 0 to 98 km.h-1 in two soil types with sandy and silty texture in a completely randomized design with three replicates. Results: The investigation of the threshold wind velocity of soil particles showed that soil particles began to move at velocity of 8 and 10 km.h-1 in silty and sandy soils, respectively, but in all biological samples (MICP), particles did not move until the wind speed reached 97 km.h-1. It was also revealed that the weight loss of all MICP-treated samples at different wind velocities was significantly reduced compared to the control group. Differences in the amount of soil loss among bio-cemented samples and control treatments were even superior at higher velocities, so that at velocities more than 57 km.h-1, soil losses increased significantly in the control group, while in soils treated with bacteria, soil loss was very low (about 2.5 kg.m-2.h-1). Comparison of the bacteria used in this study also showed that Bacillus infantis and Paenibacillus sp3 had high efficiency in controlling dust storms. Conclusion: The formation of abrasion-resistant surface layers on soil samples treated by biocementation showed that cementation by biological methods could be an effective way to stabilize surface particles and control sand and dust storms.

Relative soil water content as a factor for wind erodibility in soils with different texture and aggregation

Abstract The soil water content is one of the main factors influencing the beginning of soil particle movement by the wind. Although, some authors studied the effect of soil water content on threshold wind velocity and have defined a value to prevent wind erosion, the critical relative soil water content (HRc), most of them used disturbed and/or sieved soil samples. Under these conditions, the effect of aggregation, i.e. the natural state of the soil, cannot be evaluated. So, our objective was to determine HRc in soils with different textures in Semiarid Argentinian Pampas Region (SAPR) using uncrushed soil samples under variable wind velocities. Wind tunnel simulations were performed at three wind speeds (2.1, 8.0 and 10.5 m s−1) during 3 min in each case. Results indicated that the quantity of collected soil (Q) decreased with increasing relative soil water contents (HR) up to a HRc value at which it became negligible. HRc values were lower in fine textured soils than in coarse soils. All soils showed increasing HRc values as wind velocity increased from 2.1 to 10.5 m s−1, while the wind velocity effect is more important in coarse textured soils. HRc was negatively related to micro-aggregation in a linear way. For that reason, soils with high fine silt and clay content need lower HRc values to inhibit wind erosion. In conclusion, not only texture is important factor in defining the HRc value at a specific wind velocity but also the micro and macro-aggregation of the soils.

Wind erosion changes induced by different grazing intensities in the desert steppe, Northern China

Desert steppes are fragile ecosystems, which generally suffer severe wind erosion hazards, especially when they experiencing external disturbances such as grazing. Therefore, the effects of grazing on the wind erosion process are very important for improving our understanding of the effects of the stocking rate on grassland degradation and enacting reasonable grazing strategies in grasslands. However, few studies have discussed the wind erosion changes induced by different grazing intensities thus far. Herein, a series of grazing experiments was carried out in a desert steppe in Urad Back Banner, Inner Mongolia. These experiments included 2 types of grasslands that are shrub dominated grassland (SDG) and grass dominated grassland (GDG). Each grassland type had 3 grazing rate treatments: no grazing as the control (CK), moderate grazing (MG), and heavy grazing (HZ). After the grazing experiments lasting for 4 years, sand traps were set in the grazing plots to detect the horizontal sand flux at different grazing intensities. In addition to the wind erosion observed, the vegetation and soil particles were also surveyed and sampled. Our results showed that the vegetation cover (VC) and aboveground biomass (AGB) in the MG and HG plots all had obvious differences compared to the CK plot, regardless of whether it was SDG or GDG. The soil particle analysis showed that the fractions of erodible particles (60–200 μm) in the MG and HG plots decreased significantly. In the GDG, the soil particles exhibited a coarsening trend from CK to HG plots for the sorting action of the wind. Suffering a grazing disturbance, the wind erosion in a desert steppe exhibited significant changes. For instance, in the SDG, the horizontal sand flux in the MG and HG plots were 1.78 and 2.06 times the sand flux in the CK plots, respectively, and, in the GDG, they were 17.86 and 56.53 times the flux in the CK plots, respectively. Except in the MG and HG plots of the GDG, the saltation height of sand was generally lower than 20 cm. In the SDG, the particle size of the entrained sand mainly ranged from 80 to 200 μm, and, in the GDG, it ranged from 80 to 300 μm. This finding also indicated the validity of Shao’s sand entrainment equation. We also found that particle size of saltating sand increased with their saltation height for the tough surface of the MG and HG plots in the GDG. Based on the different fractions of horizontal flux in different directions, we also discussed the threshold wind velocity for sand entrainment, and we confirmed that the threshold wind velocities for no grazing in SDG and GDG were approximately 16.5 m·s−1 and 15 m·s−1, respectively. Using our previous wind erosion model, we estimated the dust emission in the total desert steppe of China and found that different grazing scenarios would change the magnitude and distribution of dust emissions.

Dust uplift potential in the Taklimakan Desert: an analysis based on different wind speed measurement intervals

A wind speed data set at a temporal resolution of 1 min, observed in the hinterland of the Taklimakan Desert (Tazhong) from September 1, 2008, to August 31, 2010, was used to investigate the diurnal and seasonal cycles of high wind speeds and dust uplift potential (DUP), and to investigate the effect of wind speed measurement time on the DUP in different seasons. The results suggested that high wind speeds, i.e., greater than the threshold wind velocity (TWV) for wind erosion, mainly occurred during the daytime (08:00–20:00) and the frequency of wind speeds above the TWV exhibited a large variability from season to season: spring (6.4%) > summer (5.6%) > autumn (1.7%) > winter (0.8%). The cumulative DUP was 50% on June 17 and increased to 90% on September 1, with 75.4% of the DUP generated between April 1 and July 31 over the 2-year study period. The results indicated that a different temporal resolution of wind speed affected the calculation of DUP. The DUP was 9.93 × 106 m3/s3 when wind speed was measured at 1 min, 8.96 × 106 m3/s3 at 5 min, 8.51 × 106 m3/s3 at 10 min, and 8.32 × 106 m3/s3 at 15 min. The discrepancies in the DUP when wind speed was measured at different time intervals followed the order of winter > summer > autumn > spring. From an analysis of the diurnal DUP and wind speeds measured at different time intervals, it was found that the main deviation occurred in the early morning and later at night. If the mean wind speed was measured over a time interval of 10 min or longer, there was a certain error in evaluating the damage from eolian activities.

Simulated and observed horizontal inhomogeneities of optical thickness of Arctic stratus

Abstract. Two-dimensional horizontal fields of cloud optical thickness τ derived from airborne measurements of solar spectral, cloud-reflected radiance are compared with semi-idealized large eddy simulations (LESs) of Arctic stratus performed with the Consortium for Small-scale Modeling (COSMO) atmospheric model. The measurements were collected during the Vertical Distribution of Ice in Arctic Clouds (VERDI) campaign carried out in Inuvik, Canada, in April/May 2012. The input for the LESs is obtained from collocated airborne dropsonde observations of a persistent Arctic stratus above the sea-ice-free Beaufort Sea. Simulations are performed for spatial resolutions of 50 m (1.6 km × 1.6 km domain) and 100 m (6.4 km × 6.4 km domain). Macrophysical cloud properties, such as cloud top altitude and vertical extent, are well captured by the COSMO simulations. However, COSMO produces rather homogeneous clouds compared to the measurements, in particular for the simulations with coarser spatial resolution. For both spatial resolutions, the directional structure of the cloud inhomogeneity is well represented by the model. Differences between the individual cases are mainly associated with the wind shear near cloud top and the vertical structure of the atmospheric boundary layer. A sensitivity study changing the wind velocity in COSMO by a vertically constant scaling factor shows that the directional, small-scale cloud inhomogeneity structures can range from 250 to 800 m, depending on the mean wind speed, if the simulated domain is large enough to capture also large-scale structures, which then influence the small-scale structures. For those cases, a threshold wind velocity is identified, which determines when the cloud inhomogeneity stops increasing with increasing wind velocity.

Interactive effects of wind speed, vegetation coverage and soil moisture in controlling wind erosion in a temperate desert steppe, Inner Mongolia of China

The rapid desertification of grasslands in Inner Mongolia of China poses a significant ecological threaten to northern China. The combined effects of anthropogenic disturbances (e.g., overgrazing) and biophysical processes (e.g., soil erosion) have led to vegetation degradation and the consequent acceleration of regional desertification. Thus, mitigating the accelerated wind erosion, a cause and effect of grassland desertification, is critical for the sustainable management of grasslands. Here, a combination of mobile wind tunnel experiments and wind erosion model was used to explore the effects of different levels of vegetation coverage, soil moisture and wind speed on wind erosion at different positions of a slope inside an enclosed desert steppe in the Xilamuren grassland of Inner Mongolia. The results indicated a significant spatial difference in wind erosion intensities depending on the vegetation coverage, with a strong decreasing trend from the top to the base of the slope. Increasing vegetation coverage resulted in a rapid decrease in wind erosion as explained by a power function correlation. Vegetation coverage was found to be a dominant control on wind erosion by increasing the surface roughness and by lowering the threshold wind velocity for erosion. The critical vegetation coverage required for effectively controlling wind erosion was found to be higher than 60%. Further, the wind erosion rates were negatively correlated with surface soil moisture and the mass flux in aeolian sand transport increased with increasing wind speed. We developed a mathematical model of wind erosion based on the results of an orthogonal array design. The results from the model simulation indicated that the standardized regression coefficients of the main effects of the three factors (vegetation coverage, soil moisture and wind speed) on the mass flux in aeolian sand transport were in the following order: wind speed>vegetation coverage>soil moisture. These three factors had different levels of interactive effects on the mass flux in aeolian sand transport. Our results will improve the understanding of the interactive effects of wind speed, vegetation coverage and soil moisture in controlling wind erosion in desert steppes, and will be helpful for the design of desertification control programs in future.

Resuspension of ash after the 2014 phreatic eruption at Ontake volcano, Japan

We determined the resuspension process of an ash deposit after the phreatic eruption of September 27th, 2014 at Ontake volcano, Japan, by analyzing the time series data of particle concentrations obtained using an optical particle counter and the characteristics of an ash sample. The time series of particle concentration was obtained by an optical particle counter installed 11km from the volcano from September 21st to October 19th, 2014. The time series contains counts of dust particles (ash and soil), pollen, and water drops, and was corrected to calculate the concentration of dust particles based on a polarization factor reflecting the optical anisotropy of particles. The dust concentration was compared with the time series of wind velocity. The dust concentration was high and the correlation coefficient with wind velocity was positive from September 28th to October 2nd. Grain-size analysis of an ash sample confirmed that the ash deposit contains abundant very fine particles (<30μm). Simple theoretical calculations revealed that the daily peaks of the moderate wind (a few m/s at 10m above the ground surface) were comparable with the threshold wind velocity for resuspension of an unconsolidated deposit with a wide range of particle densities. These results demonstrate that moderate wind drove the resuspension of an ash deposit containing abundant fine particles produced by the phreatic eruption.

Dust Uplift Potential in the Central Sahel: An Analysis Based on 10 years of Meteorological Measurements at High Temporal Resolution

AbstractA 10 year data set of wind speed and precipitation recorded in two Sahelian stations located in Niger and Mali is used to investigate the duration and the diurnal and seasonal cycles of high wind speeds and Dust Uplift Potential (DUP). The results indicate that high wind speeds, those greater than the threshold wind velocity required to initiate wind erosion (TWV) over a bare soil occurred in the middle and late morning during the dry and wet seasons but also at nighttime during the wet season. However, the morning wind speeds are only slightly greater than TWV leading to low DUP. On the opposite, the high wind velocities associated to the nocturnal mesoscale convective systems crossing the Sahel during the wet season are responsible for the highest potential wind erosion events. This leads to a strong seasonality of DUP with more than 70% occurring in less than 90 days, from mid‐April to mid‐July. The duration of the high wind speed events is very short since more than 80% last for less than 3 h, suggesting that the frequency of the observations performed in SYNOP meteorological stations is not sufficient to correctly quantify the contribution of such events to DUP. Finally, by combining precipitation and DUP, we estimated that precipitation should have a relatively limited role in terms of inhibition of wind erosion in this region with precipitation only affecting 25% of total DUP.

Crop residue harvest impacts wind erodibility and simulated soil loss in the Central Great Plains

AbstractCrop residue removal can affect the susceptibility to soil wind erosion in climates such as those of the Central Great Plains, United States. Six on‐farm trials were conducted in Kansas from 2011 to 2013 to determine the effects of winter wheat (Triticum aestivum L.), corn (Zea mays L.), and grain sorghum (Sorghum bicolor (L.) Moench), residue removal at 0, 25, 50, 75, and 100% of initial height on soil wind erosion parameters. Those parameters include soil surface random roughness (RR), and wind erodible fraction (EF; aggregates &lt;0.84 mm), geometric mean diameter (GMD) and geometric standard deviation (GSD), stability of dry aggregates (DAS). Complete (100%) residue removal decreased the surface RR, increased EF, and decreased GMD. Overwinter EF values increased for five of six sites from fall 2011 to spring of 2012, particularly for the uppermost removal height (≥75%). Measured EF, GMD, GSD, DAS, and RR were also input into the Single‐event Wind Erosion Evaluation Program (SWEEP) to determine the effect of these parameters on simulated soil loss. The SWEEP simulated the wind velocity needed to initiate wind erosion as well as soil loss under each residue removal height at a wind velocity of 13 m s−1 for three hours. Threshold wind velocity required to initiate wind erosion generally decreased with increasing crop residue removal height, particularly for &gt;75% removal. Total estimated soil loss over the three‐hour event ranged from ≈2 to 25 Mg ha−1, depending on EF, GMD, GSD, RR, and percent crop residue cover. Removing 75% residue increased simulated wind erosion at three of six sites while removing 50% appears sustainable at all six study sites. Findings reinforce the need for site‐by‐site consideration of the potential amount of crop residue that may be harvested while mitigating wind erosion. Study results indicate the value of maintaining residue at &gt;75% of original height.

Design of a windbreak fence to reduce fugitive dust in open areas

The wind characteristics of the Saemangeum reclaimed land are quite different from those of inland because of the prevalence of strong wind environments near the seashore. Thus, the probability of fugitive dust dispersion would be higher under these wind environmental conditions, and civil complaints regarding fugitive dust have increased in the residential area. Therefore, we must establish countermeasures to reduce fugitive dust. In this study, the dispersion behavior of fugitive dust at the Saemangeum reclaimed land was simulated by using a two-dimensional CFD simulation. A CFD model was simulated by considering the wind velocity and the design properties of the windbreak fences, such as their height, installation interval and number of layer. The percent of upstream velocity (PUV) is applied in this study to quantitatively evaluate the reduction in the wind velocity by a windbreak fence. The behavior of saltating dust was analyzed by comparing the simulation results with the threshold wind velocity, which is the wind velocity at which the soil particulates come off the surface and erosion starts. The behavior of suspended dust was analyzed by using the reduction rate of dust concentration according to the installation conditions of the windbreak fence. A strategy for installing windbreak fences was suggested according to these results to reduce fugitive dust in the Saemangeum reclaimed land.

New criteria for assessing low wind environment at pedestrian level in Hong Kong

The choice of proper wind comfort criterion is considered to be crucial to reliable assessment of pedestrian level wind comfort. This paper aims to propose a wind comfort criterion that can be applied to Hong Kong, in which the wind comfort is seriously deteriorated by the moderated airflow, particularly in the hot and humid summer. By thoroughly reviewing and comparing exiting wind comfort criteria, the parameters in Lawson (1978) criterion are adopted for acceptable, tolerable and intolerable category and the parameters in NEN8100 (2006) criterion are adopted for danger category in the proposed criteria. Besides, a low wind parameter suggested by AVA scheme (2005) is adopted for unfavourable category in summer criterion. The adopted parameters provide scientific foundations and they are carefully chosen to adapt the weak wind conditions. The prominent features of the criteria are proposed seasonally (summer and winter, respectively) and the overall mean wind velocity ratio (OMVR) is used as threshold wind velocity parameter. The wind tunnel tests of Hong Kong Polytechnic University (HKPolyU) campus model were used as a case study. The results show that the proposed criteria can reasonably represent the weak wind condition and provide suitable assessments of the wind comfort in Hong Kong. Moreover, the findings in this study provide scientific basis for future policy-making and the proposed criteria can also help city planners to improve the pedestrian level wind comfort.