Field determination for roughness length above the different non-erodible surfaces

摘要

Non-erodible elements,for its disturbance to the near-surface airflow,have been widely used in arid and semi-arid regions to protect the surface from wind erosion.Roughness length was usually used to evaluate the protection effect of non-erodible elements from wind erosion.In this study,the wind profiles above five types of non-erodible surfaces including gravel,wheat straw checkerboard barriers,cotton stem checkerboard barriers,shrubs,and herbs were measured and analyzed.The wind velocities above these surfaces increased with height approximately in logarithmic functions.The roughness length of different non-erodible surfaces was calculated by the functions of wind profiles.The results reveal that:(1) Roughness length increased with wind velocity in given wind velocity ranges.(2) On vegetative surfaces,wind did not effectively bend the stems.The threshold wind velocity for bending the stems ofAchnatherum splendens was 4 m/s,10 rr/s forAgropyron cristatum,and forArtemisia ordosica,no obvious bending of stems even for wind velocity reaching 12 m/s.(3) Correlation analysis results show that the vegetation's coverage and frontal area affect the roughness length more significantly than the other parameters.(4) The protective results of these non-erodible elements were evaluated.The checkerboard sand barriers made of cotton stem could provide more effective protection than that made of wheat straw.In the same coverage conditions,vegetation could provide more effective protection from wind erosion than gravel,and the blending of different non-erodible elements especially the combination of blending of vegeation and checkerboard sand barriers could provide more effective protection to the surface.