Contrastive Study on Sand Drift Movement over Sandl and and Gravel Gobi Desert in Extremely Arid Regions——A Case Study on Sand Drift Movement over Mogao Grottoes in Dunhuang

After analyzing the field-observed data,in this paper it is revealed that sand drift structures over sandy lands are different under different wind directions when wind speed is similar,that is sediment concentration affects sand drift structure.Generally,the absolute sand transport at all heights of windstream is increased with the increase of sediment concentration,whereas the relative sand transport is increased at lower height but decreased at upper height. However,there is also an inconsistent situation,in this field observation,for example,the sand transport was decreased at lower height but increased at upper height.Sand drift structure over Gobi desert is significantly different from that over mobile sandland.The roughness of Gobi surface increases with the increase of wind speed.With the increase of windstream height,the sand transport rate over Gobi desert has a unique elephant nose effect,that is the sand transport comes to a maximum value at certain height,and this height is increased with the increase of wind speed.Field observation reveals that sand transport is gradually decreased from Mingsha Mountain to Mogao Grottoes under northwest wind.Gobi desert with rough surface can block sand to a certain extent,and the sand blocking rate per hundred meters can be as high as 10% when wind speed is 7.7 m·s-1.Sand transport under northwest wind can be reduced by 95% after taking some measures for controlling sand drift.Northeast wind plays an important role in sand transport,sand transport under south wind is obviously less than that under northwest wind due to insufficient sand sources,and sand transport is gradually decreased from the sand-resource areas to Mogao Grottoes.