Semiarid Northern Sand Activities Coupled Relationship, And Vegetation Conditions

The north semiarid regions in China mainly distribute in the eastern Mongolia highland and the Loess plateau, and its unique natural conditions and ecosystem have formed the north-China important ecological protective screen. Being located in semiarid regions, the boundary of Hebei province and the southeastern Inner Mongolia Autonomous Region are the typical staggered areas of animal husbandry and the agriculture, therefore, the land use type is changeable. The studies of relation between vegetation conditions and dust storm activities in this region can offer important theory support for the vegetation restore and the ecological environment protection of Beijing and Tianjin periphery region.In order to investigate the relationship between vegetation conditions and dust storm activities, an indoor environmental wind tunnel has been built. It is 13.3 m in length, including fan, connection section, rectification section, stable section, experiment section of 2.3 m in length, diffusion section and dust-clearing section, and the size of cross section is 50×50 cm. The velocity of wind tunnel ranges from 0 to 20 m/s and can be changed continuously. The test results of wind tunnel show this environmental wind tunnel meets the requirement of similar principle, according to the theory of nature atmospheric boundary, so there are enough evidences to carry out the experiment of wind tunnel.By imitating the activity of dust storm under natural condition in wind tunnel, a series of experiments were carried out to investigate the influences on wind velocity distribution and surface aerodynamics parameter, minimum wind velocity of sand movement, wind erosion rate and its vertical distribution in different vegetation conditions (altitude, row spacing, distance of plants, vegetation coverage rate and vegetation lateral coverage rate). On the basis of data analysis, a wind erosion rate model in different vegetation conditions has been suggested.Compared with the distribution of near-land wind velocity of the bare and the vegetation ground, the existence of vegetation changed the distribution of near-land wind velocity, which doesn't agree with the logarithm regulation, and the wind velocity distribution can be divided into two parts by the vegetation altitude: the lower part is rough layer, and the upper part is inertia layer. The decrement, of wind velocity shows an exponentially increasing tendency with vegetation lateral coverage rate. And it also shows an exponentially decreasing tendency with row spacing and distance of plants of vegetation model. The effects of plant distance on minimizing wind velocity are more significant than those of row spacing. Aerodynamics roughness length (ARL) is an important parameter to measure the convexity extent of surface. The change of ARL with the vegetation lateral coverage rate shows the exponential tendency, which can be expressed by Z0=a5+b5 exp(c5 .p). ARL of random form of plants is higher than that of superposition. On the basis of summering the existed wind erosion rate model, three parameters have been introduced in order to describe vegetation conditions: vegetation coverage rate, vegetation lateral coverage rate and vegetation arrangement coefficient. A wind erosion rate model has been suggested according to the theory and experimental data:Model verification result shows that this model can be used to evaluate effects of vegetation on the wind erosion rate. Besides, the vertical distribution of wind erosion rate has been researched, and the results have been analyzed by comparing with the wild wind erosion rate.