| Populus euphratica nebkha is a kind of aeolian landform caused by either the sand material accumulation or disturbed action of the wind.In the filed of aeolian landforms,there were been few studies done on P.euphratica nebkhas.To the west side of the Hotan River and to the south of Hemp-tager mountain,there are a large number of P.euphratica nebkhas in Beilikum Desert in the west of Taklimakan Desert.Information of P.euphratica nebkhas landforms were extracted and calculated based on the field data achieved by geomagnetic RTK measuring method,with the support of ArcGIS and SPSS software.By the interpretation of Lsandsat8 OLI images,the spatial pattern of duens will be analysed.Based on the elevation of phreatic aquifer,the phreatic aquifer will be construct ed by spatial interpolation.The high precision DEM is constructed by the Insar.The DTM of groundwater will be produced by the phreatic aquifer and DEM.Using ArcGIS to analyse the response of P.euphratica nebkhas to the groundwater.Populus euphratica and P.euphratica nebkhas in the Beilikum Desert were measured and was taken as sampling and the 1:1 modeling of Populus euphratica and P.euphratica nebkhas are established according the sampling data.In the Geometry module of ANSYS software,we numerically simulated the single Populus euphratica and P.euphratica nebkhas in Fluid flow(Fluent)with the wind velocity divided into three groups for 6 m/s,10 m/s and 14 m/s,the characteristics of air flow structure around single Populus euphratica and P.euphratica nebkhas are derived.The result shows that there is big difference of shape of dunes in spots and there are good relationships among the morphological parameters.The horizontal shape of dunes are irregular and the three-dimensional shape is like a tapered.The surface slope of dunes is from 0° to 50°.There are totally 1171353 pixel of dues and the total area are 263554425m2.The water conditions have a big influence in the density,shape complexity of spatial distributions,and distributed continuity of dunes.The dunes develop to the south in general.The phreatic aquifer leans southwest to northeast and the largest elevation is 1229.73m and the smallest is 1117.67m.The range of the depth of groundwater is from-18.45m to 61.45m and-18.45m?0m is "lowland of lake",which is steaming.The best depth of groundwater for the growing of dunes is 5.87m.Numerical simulation shows that airflow velocity decreases in the area where it is as long as 1/3 H and as high as 1/2 H before Populus euphratica(H stands for the height of Populus euphratica).Airflow would be accelerated in the area where it is as high as about 2/3 H above the Populus euphratica and the both sides of Populus euphratica.There is a weak vortex range in the distance from 1 H to 2 H after Populus euphratica.It is a low pressure area in the windward slope of P.euphratica nebkhas,the air flow is reduced.It lays in the flow acceleration area above the top P.euphratica nebkhas as high as 2-3 H,air velocity is increased significantly.It is a negative pressure area at the leeward slope of P.euphratica nebkhas.The airflow around flow velocity decreases significantly and would be formed a vortex range in the leeward slope within a certain distance.Through measuring the Populus euphratica grain size distribution of top aeolian soil,it can be indirectly validated the flow field characteristics of P.euphratica nebkhas.Populus euphratica can increase the roughness of land surface,the running of the air flow is interfered,and the energy of airflow is significantly reduced,so that the structure of the airflow can be changed.Eventually,sand materials in the air can be deposited in different parts of P.euphratica nebkhas,which has important significance for promoting the development of P.euphratica nebkhas and maintaining the topography of P.euphratica nebkhas and sand-fixation effects.Populus euphratica in different geomorphological positions of surface soil particles show regular changes,the average particle size from the windward slope toe to leeward slope gradually tapering from the leeward slope to the leeward slope slope becomes thick... |
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