Liqiang Kang

Cogitation on developing a dynamic model of soil wind erosion

Studies on soil wind erosion began with single factors affecting soil wind erosion; with increasing quantities of data being accumulated, the wind erosion equation (WEQ), the revised wind erosion equation (RWEQ), the wind erosion prediction system (WEPS), and other soil wind erosion models have been successively established, and great advances have been achieved. Here we briefly review the soil wind erosion research course and analyze the advantages and disadvantages of the current soil wind erosion models. From the perspective of the dynamics of wind erosion, we classified the factors affecting soil wind erosion into three categories, namely, wind erosivity factors (WEF), soil antierodibility factors (SAF), and roughness interference factors (RIF). We proposed the concept of a standard plot of soil wind erosion to solve the problem of uncertainty of the soil wind erosion modulus on a spatial scale, and provided methods to set similarity conditions in wind tunnel simulation experiments and to convert the spatial scale of the wind erosion modulus from the standard plot to a large scale field. We also proposed a conceptual model on the basis of the dynamics of soil wind erosion with the theoretical basis that wind produces a shear force on the soil surface. This shear force is partitioned by barely erodible soil surfaces and roughness elements on the ground, and the amount of soil loss by wind should be calculated by comparing the shear force of the wind on barely erodible soil surfaces with the anti-erosion force of the surface soil. One advantage of this conceptual model is that the calculated soil wind erosion modulus is not subject to changes of spatial scale. Finally, we recommended continual improvement of the existing models while also establishing new models.

Aeolian creeping mass of different grain sizes over sand beds of varying length

Creep is an important mode of aeolian sand transport, but it has received little attention in previous studies due to experimental difficulties and insufficient theory. In this study, we conducted 116 groups of experiments with three repeats for each group in a wind tunnel to measure the creeping mass of four different mean grain sizes (152, 257, 321, and 382 µm) over six bed lengths (2.0, 3.5, 5.0, 6.5, 8.0, and 10.0 m) at six different friction velocities (0.23, 0.35, 0.41, 0.47, 0.55, and 0.61 m/s). We attempted to develop a comprehensive model of the aeolian creeping mass by analyzing the effect of wind velocity, the particle size, and the sand bed length based on the experimental data. The primary conclusions are as follows: (1) the complex relationship among the wind velocity, the grain size, the length of the bed, and the surface shape determines sand creep. There was no unified formula to express the effect of particle sizes and the sand bed length on aeolian creeping masses, and their effects appeared to depend on each other and wind velocity, whereas the creeping mass increases with increasing wind velocity for any particle size with any length of sand bed. (2) This paper presented a predicting model to determine the aeolian creeping mass, whose calculating results can match to experimental data with correlation coefficients (R2) of 0.94 or higher. (3) The effect of grain size on creeping mass can be classified into three categories: the creeping mass increases with increasing grain size, the creeping mass initially decreases and subsequently increases with increasing grain size, and the creeping mass fluctuates with the grain size. (4) The effect of increasing bed length appears to depend on the grain size. For mean grain sizes of 152, 257, and 321 µm, creep initially increases with increasing bed length before decreasing above a certain value, while for a mean grain size of 382 µm, the creeping mass gradually increased with increasing bed length. The results help to elucidate aeolian creep and provide an intense foundation for advanced study.

Experimental study of aeolian sand ripples in a wind tunnel

The topographic parameters and propagation velocity of Aeolian sand ripples reflect complex erosion, transport, and deposition processes of sand on the land surface. In this study, three Nikon cameras located in the windward (0-1 m), middle (4.5-5.5 m), and downwind (9-10 m) zones of a 10-m long sand bed are used to continuously record changes in sand ripples. Based on the data extracted from these images, this study reaches the following conclusions: 1) The initial formation and full development times of sand ripples over a flatbed decrease with wind velocity. 2) The wavelengths of full development sand ripples are approximately twice the wavelengths of initially formed sand ripples. Both wavelengths increase linearly with friction velocity. During the developing stage of sand ripples, the wavelength increases linearly with time. 3) The propagation velocity of full development sand ripples is approximately 0.6 times that of the initially formed sand ripples. Both wavelengths increase as power functions with respect to friction velocity. During the developing stage of sand ripples, the propagation velocity decreases with time following a power law. These results provide new information for understanding the formation and evolution of aeolian sand ripples and help improve numerical simulations.

Experimental Investigation on Shear-Stress Partitioning for Flexible Plants with Approximately Zero Basal-to-Frontal Area Ratio in a Wind Tunnel

Shear-stress partitioning is investigated for one type of flexible plant for very small values of the basal-to-frontal area ratio σ (0.001–0.007). The plant model is made of plastic with irregular structures, which are different from previously investigated rigid regular or flexible roughness elements with larger σ values. The distribution of the surface shear stress and the total shear stress at four plant densities with five plant heights are measured in a wind tunnel using Irwin-type sensors and a load cell, respectively. The wind-tunnel experiments prove that, for these flexible plants, the plant height and lateral cover usually decrease with increasing friction velocity, especially for taller plants, while the plant coverage generally increases. However, these characteristics may be inconsistent with flexible roughness elements with very large σ values (and usually very low aspect ratios) because these elements are less flexible. The present flexible plants generally result in lower shear-stress ratios compared with other roughness elements, which is also proven by the higher values of β (the ratio of the drag coefficient of an isolated roughness element to that of the bare surface) and a constant m (accounting for the difference between the average and peak surface shear stresses) from the present experiments (β = 184–210 and m = 0.68–0.79). The peak mean stress ratio of the present flexible plants is not a constant (1.07–1.54) because it is affected by the lateral cover, which is different from previous studies that consider the ratio to be constant without regard for the lateral cover.

Influence of dust storms on atmospheric particulate pollution and acid rain in northern China

Northern China is the area with the highest incidence of dust storms in the world, which are the main sources of its soil dust emissions. In addition, the region consumes huge amounts of fossil fuels and has serious atmospheric particulate pollution. Existing observation results show that a single dust storm has significant influence on atmospheric particulate pollutant concentrations and precipitation acidity. Proving the influence of dust storms on atmospheric particulate pollution, acid rain, and the acid rain ratio and determining whether there is a causal relationship among them on a longer time scale will help us recognize the impact of dust storms on the atmospheric environment. This paper proves that dust storms are the direct cause of the variations in the number of acid rain days and acid rain ratio, as well as the changes in atmospheric particulate pollution, in spring by using the Granger Causality Test and correlation analysis methods based on 1993 to 2007 data, including the number of days of dust storms, atmospheric particulate pollution, and acid rain. Atmospheric particulate pollution is the direct cause of variations in the number of acid rain days and the acid rain ratio in spring; for the other seasons, additional data combined with atmospheric particulate pollution are needed to explain the causes of the acid rain day and ratio changes.