2.3 Ridge microtopography model and drifting sand flux structure measurement
The ridge models are constructed by two wood boards joined together, creating a triangular cross-section. The angle between the boards at the peak of the ridge was 90°, and the slope angle was 45°, so the cross-section formed an isosceles triangle. The heights (H) of the ridge models were 5, 7.5, 10, 12.5 and 15 cm respectively, and the ridge spacing (L) was 5H, 10H, 15H, 20H, and 25H respectively, totally 25 ridge structures. At the central axis of the wind tunnel floor, there is a sample trough, 1 m wide, 10 m long, and 3 cm deep . We collected a sandy soil from the Zhenglan Banner of Inner Mongolia, in northern China. The grain-size composition of the soil was provided by (Jia et al., 2019). In wind erosion experiments, soil samples were spread in the whole sample trough. Soil surface was smoothed and then the ridge models were laid on it. A sand sampler was arranged at the end of the sample trough to collect sand at different heights. The sand sampler is a special sand sampler for wind tunnel developed and produced by the MOE Engineering Research Center of Desertification and Blown-sand Control of Beijing Normal University, which is composed by a bracket and seven sand collecting boxes, with a height of 70 cm, and the cross-sectional area of each sand inlet is 10 cm × 10 cm. The sand flow within the height range of 70 cm above the bed surface can be collected. The sand collecting box is rectangular, sealed at the bottom, wedge-shaped at the opening end, stainless steel on three sides and mesh one side, which serves as an exhaust port to discharge the air flow in the sand collecting box. The inlet end of the sand collection box is designed to be wedge-shaped, which can effectively relieve the blocking airflow at the inlet and effectively improve the sand collection efficiency (Fig.1). After each blowing experiment, the sand collecting box was taken out one by one, and the sand mass was measured by an electronic balance to calculate the structure of drifting sand flux and sand transport rate.
RESULTS AND ANALYSIS