The Preliminary Research About The Characteristic Of Grain Size And The Cause Of Vegetation Dunes In Hetian River Drainage Area

The Hetian river drainage is located in the Xinjiang Tarim Basin southern fringe,the relief of Hetian river drainage is that sourth is high and north is low , the southern part is an alpine region , central section is low mountain hills area. The oasis distributes the middle in the alluvial plain mainly ,extends to Tarim Basin. Winter climate is drying and frigidity , summer has little rain and high temperature. From the analysis on the spot and reconnaissance report, the Hetian river drainage is distributing large area dust Yang Lin and rose willow shrub forest.Vegetation dune is a kind of typical Aeolian landform.The wind power, sand source and plant are mainly influencing factors of the development of Vegetation dune.Vegetation dune has the distinctive effect in attributing the earth's surface process , area environment evolution and land coverage change. The Subject investigated of this paper is with Vegetation Dunes in Hetian River Drainage Area,utilie geomorphology method , on basis inspecting and observing in the open country, testing the analytical means combining with the deposit size experiment , air tunnel simulation experiment etc. Wielding sand blown by the wind, tests the analytical means combining with the deposit size experiment , air tunnel simulation experiment etc. Study unitized matter and erodes product process of Vegetation Dunes in Hetian River Drainage Area .the first step ,studies the nature and quantify relation and main factors that effect development of Vegetation Dunes ,such as wind speed , sand source , vegetation .Developing can contrasting with to some extent and supplement with the result studying other. This enriches our country sand geomorphology content, forecasts the arid area land desertification developing trend , ensures oasis organism's habits safety to have importance.In this paper,we have researched the characteristic of grain size and the cause of Vegetation Dunes in Hetian River Drainage Area. Basic conclusion is as follows : The main mechanical sediments components of Vegetation Dunes is sand in Hetian River Drainage Area, silt, clay is little, and very little gravel sand content, the average particle size distribution in 1.99Φ-4.06Φ, average is 3.46Φ. The sand particle size of Vegetation Dunes was regular pattern change on different parts,the sand particle size of windward base of slope and middle slope is rough on the leeward side , sediment particle size of slope'tip is minimum. I believe the sand particle size of Vegetation Dunes on different parts that have relation to the winds and the source of material, meanwhile the plant of dunes will increase the surface roughness of the sand to block airflow dissipation. So changes in the structure of flow in Nebkhas showing the corresponding particle size characteristics on different parts. Largely from the dunes patterns can be measured in hemispherical and cones, there are two characteristics of the difference in size. The difference was mainly due to the shape as a result of the velocity and pressure in different parts caused by the differences.