Research paperField observations of sand transport over the crest of a transverse dune in northwestern China Tengger Desert

•The modified Charnock model provides the best relationship between u* and z0.•Sand transport is negatively correlated to the wind direction.•There is a critical wind direction over the dune crest for sand transport.

Dune movement processes are affected by various sand transport processes, especially at the dune crest; however, there are relatively few field measurements on this issue. In this paper, 76 field measurements were collected over a dune crest at the Shapotou Aeolian Experiment Site, northeastern Tengger Desert, China to measure the rate of sand transportation under filed conditions. The measured sand transport rate ranged from 0.2 to 121.2 kg m−1 h−1, and most (95%) were less than 67 kg m−1 h−1. The roughness length calculated from the wind profiles was much larger than the results of previous studies. A linear regression analysis indicated that the modified Charnock model gives the best relationship fit between the shear velocity and roughness length (Cm = 0.432, n = 76, p < 0.0001, R2 = 0.997). The sand transport flux over the dune crest can be expressed as an exponential function and a Gaussian function. A correlation coefficient analysis of the complex relationship between the sand transport and wind conditions (mean velocity, maximum wind velocity, shear velocity, potential sand transport, and wind direction) and the surface properties (roughness length, fetch length) indicated that the sand transport rate over the dune crest is positively correlated with the mean velocity (n = 76, p < 0.0001, R2 = 0.58) and shear velocity (n = 76, p <  0.0001, R2 = 0.57) and is negatively correlated with the wind direction (n = 76, p < 0.0001, R2 = −0.37). The wind direction affects sand transport over the dune crest and the coefficients of the sand transport flux. The critical wind direction is 272°, which is approximately perpendicular to the line of the crest (37°).