Mcro-gradient Observation Study Of The Sand Flow Of Taklimakan Desert

Sand sample datas are collected by Micro-gradient sand trap from July 2014 to August 2014 in Ta Zhong of the taklamakan desert.This study focuses on the micro-gradient structure of wind-sand flow and analyzes the change of saltation and creep with different wind speed in the typical weather.Reveal the characteristics of the micro-gradient wind-sand flow of TaZhong.The major conclusions of this study are as follows:(1) In typical weather,at each height level sediment transport rate increases with the increase of wind speed.For the Jansa weather,when the wind speed is less than 6.3 m/s,the increase of each height level transport rate is not obvious,but when the wind speed is greater than 6.3m/s,at each height level sediment transport rate significantly increased.When wind speed is greater than 8.1m/s,at 0 to 5mm(creep layer) and 15 to 35 mm height level difference of sediment transport rate gradually opened.When the wind speed is less than 9.2m/s,at 5-15 mm height level transport rate is the largest.after the 9.2m/s, at 0 to 5mm height level(creep layer) sediment transport rate reaches the maximum, but at 35-85 mm height level the change of sediment transport rate is not obvious;For the sandstorm weather,changing trends in sediment transport rate at each height level are similar with the Jansa weather,turning point appears in 7.2m/s,before it,the increase of sediment transport rate was not significant,after it,sediment transport rate increased significantly.(2) Best-fit relationship of wind speed and sediment transport rate at each height level is the power function with wind speed and total sediment transport rate.For total sediment transport rate,when the wind speed is less than about 6 to 7m/s,total sediment transport rate showed increasing trend,but slowly.when the wind speed is more than 6 to 7m/s,increasing obviously;For each height level,the effect of wind speed on sediment transport rate at each height level is the range of 0 to 35 mm.(3) In typical weather,percentage at 0 to 5mm and 15 to 35 mm height level basically shows upward trend, percentage at 5 to 15 mm and 35 to 85 mm height level basically shows downward trend.Change of percentage at 15 to 35 mm and 35 to 85 mm height level is the most obvious,percentage at 0 to 5mm(creep layer) height level does not change significantly.When the wind speed reaches about 8.0 m/s,percentage at 15 to 35 mm height level reaches the maximum.In two weather,inflection point appears about at 9.0m/s,percentage changes obviously before,after it,percentage has a stable trend.(4) Best-fit relationship of wind speed and percentage at each height level is the power function and exponential function.The sediment discharge is more and more concentrated within 0 to 35 mm height level from the function parameters.(5) In typical weather, both of peak of particle size are at 125-250μm.Very fine sand has the highest content followed by fine sand,and the two account for more than 90% of sediment discharge.The maximum of content about fine sand appears at 35-85 mm height level, and the miximum is at 15-35 mm height level.Very fine sand is in contrast with the fine sand.Compared with the Jansa weather,content of very fine sand, fine sand and sand at each height level almost is equal,while content of the dust is increased in the sandstorm weather.(6) In typical weather,at first the average particle size in the vertical height increases,then decreases.In the Jansa weather,the minimum of the average particle size appeares at the 15 to 35 mm height level,about 226μm,and the maximum appeares at the 35 to 85 mm height level,about 242μm.for the Jansa weather,the minimum of the average particle size generally appeares at the 5 to 15 mm height level,about 210μm,and the maximum appeares at the 0 to 5mm height level,about 227 μm.(7) Best-fit relationship of wind speed and the ratio of Saltation sediment discharge and creep sediment discharge is the power function and the exponential function.With the increase of wind speed, the ratio gradually decreases and eventually has a stable trend.Inflection point of wind speed appears at about 8.5m/s,and after the ratio tends to be stable,it is about between 8 to 10.With the increase of wind speed,the ratio of total saltation sediment discharge and total creep sediment discharge gradually decreases and eventually has a stable trend.Inflection point of wind speed appears at about 8.0 m/s,and the ratio about between 9 to 24 at different wind speed in typical weather.