Sand Transport Rate Research Articles

Modeling the aeolian sand transport for the desert of Kuwait: Constraints by field observations

The Kuwaiti desert is swept by strong winds, particularly by northwesterly wind, during the summer months (April through September), causing mass-scale sand transport that poses a serious environmental hazard. Understanding that accurate transport rate data are very difficult to obtain either by field measurements or by using any existing sand transport formulae, this paper presents a mathematical model to predict the sand-transport rate for Kuwaiti desert by following a well-known theoretical approach of Lettau and Lettau (1978) and by taking into account the effect of seasonal wind variability. The validity of the model is next examined using the field data from the study of Al-Awadhi and Al-Sudairawi (2002). The examination showed that the model underestimates the rate of sand transport by an average ratio of 0.15. The application of the model, at some seven locations that are evenly distributed across the Kuwaiti desert, indicated that about 40% of the amount of sand transport in Kuwait prevails from the NW during the peak summer months (June and July). The resulting map of sand transport rate indicated that the zone of higher sand transport rate is located within the areas covered by most extensive mobile sand sheets and sand dunes.

Database of full-scale laboratory experiments on wave-driven sand transport processes

A new database of laboratory experiments involving sand transport processes over horizontal, mobile sand beds under full-scale non-breaking wave and non-breaking wave-plus-current conditions is described. The database contains details of the flow and bed conditions, information on which quantities were measured and the value of the measured net sand transport rate for 298 experiments conducted in 7 large-scale laboratory facilities. Analysis of the coverage of the experiments and the measured net sand transport rates identified the following gaps in the range of test conditions and/or the type of measurements: (i) graded sand experiments, (ii) wave-plus-current experiments and (iii) intra-wave velocity and concentration measurements in the ripple regime. Furthermore, it highlights two areas requiring further research: (i) the differences in sand transport processes and sand transport rates between real waves and tunnel flows with nominally similar near-bed oscillatory flow conditions and (ii) the effects of acceleration skewness on transport rates. The database is a useful resource for the development and validation of sand transport models for coastal applications.

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.

High-frequency Field Measurements of Aeolian Sand Transport Rate at a Beach

This study conducted field observations in terms of the number of wind-blown sand impacts and wind velocity in the period of 22 September - 2 December 2005 at an open ocean beach in Japan, in order to investigate variation of the wind-blown sand transport rate. Measured transport rate was calculated using the number of wind-blown sand impacts and compared to the rate estimated from the wind velocity using Bagnold's, Kawamura's, and Owen's equations. During the measurement period, the rate estimated using Owen's equation was relatively good agreement with the measured rate and the other equations overestimate the measured rate. The rate estimated using Kawamura's equation from hourly wind data obtained at off-site significantly overestimates the measured rate more than one order. Further knowledge about the actual aeolian sand transport should be accumulated in the field.

Characteristics of Sediment Transport and Short-Term Topographic Change on the Nakatajima Dune

Short-term topographic changes of the Nakatajima dune, which is located on an eroded beach on the Enshu-Nada coast, have been investigated with continuous field surveys over two years period (2007-2009). Measurements of wind and wind-blown sand transport rate were also carried out several times in winter. Based on the field data, overall properties of the sediment transport on the dune are first described in the paper. Eastward migration of the dune is then indicated with relation to the topographic changes and the distribution of the sediment transport rate. Quantitative estimate of the average volume of transported sand are well predicted by some existing formulae

Sidewall effects of a wind tunnel on wind velocity and mass flux in aeolian sand transport

The sidewall effects of a wind tunnel on aeolian sand transport were investigated experimentally. A wind tunnel was used to conduct the experiments with a given channel height of 120 cm and varying widths ( B) of 40, 60, 80, 100 and 120 cm. Both vertical profiles of wind velocity and sand mass flux were measured at different locations across the test section. The results show that the wind velocity with saltation first increases and then decreases to a minimum, from the sidewall to the central line of the wind tunnel. The discrepancy among wind velocities at different locations of the transverse section decreases with decreasing tunnel width. The wind friction velocity across the wind tunnel floor, with the exception of the region closest to the sidewalls, does not deviate strongly in wide wind tunnels from that along the central line, whereas it does vary in narrow tunnels. The sand mass fluxes, with the exception of some near-bed regions, are larger along the central line of the wind tunnel than they are at the quarter width location from the sidewall. Unlikely previously reported results, the dimensionless sand transport rate, Qg / ( ρu ⁎ 3) (where Q is the total sand transport rate, g is the gravitational acceleration constant, ρ is the air density, and u ⁎ is the wind friction velocity), first decreases and then increases with the dimensionless friction velocity, u ⁎ / u ⁎t (where u ⁎t is the threshold friction velocity). The above differences may be attributed to the sidewall effects of the wind tunnel. A dimensionless parameter, F B = u ⁎ / ( gB) 1/2, is defined to reflect the sidewall effects on aeolian sand transport. The flows with F B of 0.33 or less may be free from the sidewall effects of the wind tunnel and can ensure accurate saltation tunnel simulation.

Sand transport under increased lateral jetting of raindrops induced by wind

Wind tunnel experiments for ‘Raindrop Detachment and Wind-Driven Transport’ (RD–WDT) process were conducted under improved lateral jetting induced by wind velocities of 6.4, 10, and 12 m s − 1 at nozzle operating pressures of 75, 100, and 150 kPa. Wind-driven rainfalls were also incident on the windward and leeward slopes of 4° and 9° to have a broad variation in the angle of incidence. The objective of this experimental set-up was to distinguish the roles of both impact components of obliquely striking wind-driven raindrops on RD and wind on WDT. Raindrop impact components and reference horizontal wind were quantified by normal ( E tz) and horizontal ( E tx) kinetic energy fluxes and wind shear velocity ( u ⁎), respectively, to physically model the process of RD–WDT. The results showed, at each level of u ⁎, differential sand transport rates by RD–WDT ( q m(RD–WDT)) occurred depending on the magnitude of raindrop impact components, and q m(RD–WDT) increased as the relative contribution of E tz increased. Although E tx was more correlated with q m(RD–WDT) than E tz, the extreme increases in E tx at the expense of E tz brought about no increases but decreases in q m(RD–WDT). An RD–WDT model was built under the process of examining the discrete effects of E tz and E tx on RD together with u ⁎ and resulted in a better coefficient of determination ( R 2 = 0.89) than only total kinetic energy ( E t) did alone with u ⁎ ( R 2 = 0.84). In this study, E tx was strongly related to u ⁎ and not to E tz, which was the principal difference from the previous rainsplash studies, which relied on the compensatory lateral jet development by the compressive pressure build-up at the raindrop–soil interface. Including E tx in the RD–WDT model both separated the distinct role of each raindrop impact component in RD and improved the performance of u ⁎ in WDT by better distinguishing its interaction with E tx, which was not explicitly separated in previous models of RD–WDT.

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 transport 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 exponential 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.

Effects of the mid-air collision on sand saltation

As to the fact that the effects of saltating particles’ mid-air collision on the sand transport rate are often neglected in the current theoretical models describing sand saltation movement, expressions to calculate velocity diversity of saltating particles after mid-air collision are presented through collision theory of hard ball in this paper. Then, the theoretical model of the wind blown sand movement at the steady state, taking account of coupled interaction between saltation particles and wind, is combined with the model of the mid-air collision probability to calculate the saltating particles’ mass flux at heights, the sand transport rate, and further, their changing rules. The comparison of the results with those when the mid-air collision is not considered suggests that the mass flux at heights and the sand transport rate in this paper are less, and much closer, respectively, to the corresponding experimental values. The difference between the sand mass fluxes without and with consideration of mid-air collision increases at first, and then decreases as the height increases, exhibiting the stratified characteristics.

Grain size and transport characteristics of non-uniform sand in aeolian saltation

Abstract Size frequency distributions of sediment particles in a wind tunnel containing a bed of non-uniform sand are investigated by re-interpreting existing experimental data using particle-size analysis. Each particle sample is classified into one of eight groups according to its size grading. The analysis reveals that the modal shape of the particle-size frequency distributions of the saltating sand at different elevations or longitudinal distances is similar to that of the mixed sand in the bed once the boundary layer is fully developed. The standard deviation of the grain-size frequency distribution increases with increasing elevation above the bed then stays constant, whereas its skewness decreases. The mean grain size decays exponentially with elevation. The aeolian sand mass flux is determined for each size grading at different vertical and horizontal measurement locations. The vertical profile of aeolian horizontal mass flux depends on the size grading. The distribution of the sand transport rate according to the mean grain size in each grading fits the normal distribution. A parameter w i is defined to reflect the likelihood of saltation for sand particles of the i -th size grading, and the mean sand size corresponding to the maximum value of w i is found to be 0.2 mm. In addition, wind velocity strongly influences the magnitudes of the particle-size distribution and the sand mass flux distribution in both vertical and longitudinal directions.

Cross‐shore suspended sand and bed load transport on beaches

Simple formulas are developed to predict the time‐averaged rates of cross‐shore suspended sand and bed load transport. The net suspended sand transport rate is expressed as the product of the depth‐averaged current and the suspended sediment volume per unit bottom area with a reduction factor that accounts for the correlation between the time‐varying fluid velocity and sediment concentration. The net bed load transport rate under nonlinear waves is assumed to be onshore and proportional to σU3 where σU is the standard deviation of the horizontal velocity. The probabilities of sediment movement and suspension are introduced to account for the initiation of sediment movement and suspension. Simple functions are proposed to account for the effects of a steep bottom slope on the bed load and suspended sediment transport rates. The proposed formulas are found to be in agreement with three data sets within a factor of about 2. The proposed formulas are shown to be consistent with existing simple formulas. The formulas are incorporated into a time‐averaged wave model and the continuity equation of bottom sediment to predict the beach profile evolution. The numerical model is compared with seven small‐scale tests including berm erosion tests and seven large‐scale tests including dune erosion tests. The numerical model predicts the overall beach profile evolution including the berm and dune erosion but does not always predict the fairly subtle profile changes including bar migration accurately.

Groundwater salinity as a control on development of eolian landscape: An example from the White Sands of New Mexico

The White Sands of southern New Mexico form the largest field of gypsum dunes in the world. The juxtaposition of several different types of dunes within the field has long been recognized and has generally been attributed to changes in the rate of sand transport across the dune field. However, Steven Fryberger [Fryberger, S.G., 2003. Geology of White Sands National Monument, web page www2.nature.nps.gov/geology/parks/whsa/] recently hypothesized, however, that a primary control is groundwater salinity. The White Sands dune field is underlain by saline waters. Fryberger proposed that parabolic dunes could form in topographic highs that accumulated a lens of fresher water derived from precipitation. Water with lower salinity allowed vegetation to grow, and stabilized the sand except for the active noses of the parabolic dunes. This study is a test of that hypothesis. A study transect was established across the boundary between parabolic and barchan dunes. Groundwater and soil at six sites were sampled during December, 2004 and March, May, and June of 2005. Two sites were established in the parabolic field, two in the barchans, and two in the transition zone between them. Groundwater was found to be three times more saline in the barchan area. Conductivity and chloride decreased across the transition zone. A GPS topographic survey revealed two abrupt topographic steps, one at the boundary between the barchans and the transition zone and a second at the edge of the parabolic field. A second, larger topographic step was found outside the study area defining a higher parabolic dune field. These data indicate that Fryberger's (2003) hypothesis is correct and groundwater is controlling the dune field morphology. The dune field did not begin to form until the Mid-Holocene (6500 years ago). A compilation of dates shows that the parabolic dune field has probably been stable for the last 3500 years. In contrast, the barchan area has been recently deflated and exposed 2000 year old sediment near the surface.

Shielding effect of oasis-protection systems composed of various forms of wind break on sand fixation in an arid region: A case study in the Hexi Corridor, northwest China

Sandstorms are catastrophic weather phenomena that occur frequently in arid and semi-arid areas, with enormous effects on the ecological environment and human health. Particularly around oases, desertification is the major obstacle to sustainable development of oases in arid regions of northwest China. At present, the problem of how to build an optimal oasis-protection system must be resolved by local farmers and scientists. This paper used data on the sand transportation rate, wind speed, and the width and water requirement of vegetative barriers to evaluate the shielding effect of an oasis-protection system. The results showed that integrating straw checkerboards, a sand-fixing plant belt, and a farmland shelterbelt provided an effective oasis-protection system in the transitional zone between an oasis and shifting dunes. The system can reduce wind speed by 70% and the sand transportation rate by 96% when wind reached the farmland after passing through the oasis-protection system. For the transitional zone between the oasis and a Gobi desert, a desert vegetation preservation belt, a windbreak belt, a mixed belt that combines production forest and forage grass, and a farmland shelterbelt also provided significant shelter, and reduced wind speed and the sand transportation rate by 70 and 80%, respectively. For an optimal oasis-protection system, the width and water requirements of the vegetation barriers were also crucial factors because water resources are an important limiting factor for maintaining vegetation barriers in the long-term.

Limited change in dune mobility in response to a large decrease in wind power in semi-arid northern China since the 1970s

The climatic controls on dune mobility, especially the relative importance of wind strength, remain incompletely understood. This is a key research problem in semi-arid northern China, both for interpreting past dune activity as evidence of paleoclimate and for predicting future environmental change. Potential eolian sand transport, which is approximately proportional to wind power above the threshold for sand entrainment, has decreased across much of northern China since the 1970s. Over the same period, effective moisture (ratio of precipitation to potential evapotranspiration) has not changed significantly. This “natural experiment” provides insight on the relative importance of wind power as a control on dune mobility in three dunefields of northern China (Mu Us, Otindag, and Horqin), although poorly understood and potentially large effects of human land use complicate interpretation. Dune forms in these three regions are consistent with sand transport vectors inferred from weather station data, suggesting that wind directions have remained stable and the stations adequately represent winds that shaped the dunes. The predicted effect of weaker winds since the 1970s would be dune stabilization, with lower sand transport rates allowing vegetation cover to expand. Large portions of all three dunefields remained stabilized by vegetation in the 1970s despite high wind power. Since the 1970s, trends in remotely sensed vegetation greenness and change in mobile dune area inferred from sequential Landsat images do indicate widespread dune stabilization in the eastern Mu Us region. On the other hand, expansion of active dunes took place farther west in the Mu Us dunefield and especially in the central Otindag dunefield, with little overall change in two parts of the Horqin dunes. Better ground truth is needed to validate the remote sensing analyses, but results presented here place limits on the relative importance of wind strength as a control on dune mobility in the study areas. High wind power alone does not completely destabilize these dunes. A large decrease in wind power either has little short-term effect on the dunes, or more likely its effect is sufficiently small that it is obscured by human impacts on dune stability in many parts of the study areas.

Sand-fixing effects of Caragana microphylla shrub in Horqin sandy land, North China

In the semi-arid Horqin sandy land of north China, Caragana microphylla, a leguminous shrub, is the dominant plant species and is widely used in vegetation reestablishment programs to stabilize shifting sand. The sand-fixing effects of 6-and 11-year-old C. microphylla plantations were studied. The results showed that: 1) the wind velocity and sand transport rate in the plantation were less than those in dunes; 2) the air temperature in the plantation was lower than those in dunes. Relative humidity was higher and the soil temperature was lower, which benefits plant growth; 3) the physical and chemical characteristics of soil were improved to some extent over age. The porosity and percentage of tiny sand (diameter 0.05–0.1 mm) and clay particle (diameter < 0.05 mm) increased, bulk density in surface soil decreased, and saturated water-holding capacity improved. Organic C, total N, available N and available K content increased gradually, and soil fertility was enhanced.

Sand Transport around North End of Shimizu Coast and Field Observation of Refilling Process after Foreshore Excavation

A submarine canyon develops around the north end of the Shimizu coast, and offshore sand loss into the submarine canyon through the steep slope has occurred. The bathymetric survey data were analyzed, and the rate of offshore sand transport was evaluated to be 160 m3/m/yr on the 0.4-km-long coastline. The foreshore excavation was experimentally carried out to investigate the capability of sand recycling from the tip of the sand spit. The rate of refilling was found to be 35m3/day in the test area.

Field Observations of Aeolian Sand Transport Rate Using a Piezoelectric Ceramic Sensor

Field Observations of Aeolian Sand Transport Rate Using a Piezoelectric Ceramic Sensor

Distribution of Horizontal Distance Traveled by Saltating Sand Grains in Air

The distribution of the horizontal distance traveled by the sand grains in saltation, which is equal to the distribution of the falling sand grain rate in the region from the end of the sand bed and down wind, is quite similar to the vertical distribution of sand transport rate above the sand surface. This observation is explained by assuming that the height of the trajectories of transported sand grains in the air is different but the trajectories are similar in form. The wind tunnel experiment showed that the equation for the distribution of horizontal distance traveled by the grains converted from the vertical distribution of sand transport rate can be applied for sand grains smaller than 0.68mm.

The dependency of sand transport rate by wind on the atmospheric stability: A numerical simulation

A theoretical model of the process for wind–sand flow is developed through consideration of the coupling between wind flow and the motion of sand particles under different atmospheric stability conditions. Using this model, we studied the effects of atmospheric stability on the sand transport rate, the number of sand particles per unit area and time, and the duration before a steady state is achieved in detail. The results show that atmospheric stability has a strong effect on the movement of the wind–sand flow, and produces results with different characteristics from those previously reported in the literature which apply only to conditions of neutral stability. Under unstable conditions, the wind–sand flow reached equilibrium more quickly, with a higher total sand flux and sand flux at all heights than under neutral or stable conditions.

Wind velocity profiles with a blowing sand boundary layer: Theoretical simulation and experimental validation

Describing wind velocity profiles modified by the movement of blown sand is of continuing significance because they are thought to bear rich information about wind‐sand interaction in a blowing sand cloud. This paper treats the saltating cloud as a fluidized particle flow and develops a mathematical model of the wind‐sand interactions. The force exerted on the air by saltating particles is characterized by introducing a drag coefficient of the fluidized aeolian particle flow that is modified after the drag coefficients proposed for liquid fluidized particle flow. The resulting model was then used to simulate wind velocity profiles in the presence of a saltation cloud on the basis of the mean particle velocity and particle concentration profiles of the fluidized particle flow obtained from wind tunnel tests. The simulated velocity profiles agree well with those directly measured in the wind tunnel. The blowing sand boundary layer is divided into a saltation subboundary layer, in which saltating particles participate in momentum exchange with the wind, and an outer subboundary layer above the saltation subboundary layer. The wind velocity profiles within the saltation subboundary layer are characterized by convex‐upward curves in a log (height)‐linear (wind velocity) plot rather than the straight lines in the velocity profiles of clean wind. The upward convexity of the velocity profiles increases as wind velocity increases, suggesting that more wind momentum is absorbed by the saltating particles as the sand transport rate increases. The wind velocity profiles in the outer subboundary layer approach the Prandtl logarithmic law with the saltation subboundary layer providing increased aerodynamic roughness. Our results suggest that the wind shear velocity in the presence of a saltation cloud is a physical dimension that can reflect the effect of saltation.