## 2 Field Experiment
### Sand Transport Environment and Analysis  
Drift Potential (_DP_) is widely used in the study of aeolian geomorphology or sand control engineering design and is the scale of surface wind energy of wind-sand activity [24; 25]. According to the formula proposed by [PERSON] [26], Drift Potential (_DP_), Resultant Drift Potential (_RDP_), and Resultant Drift Direction (_RDD_) can be calculated by the following equation:  
\[DP=V^{2}(V-V_{t})t \tag{1}\]  
where _DP_ represents drift potential of which the unit is VU; _Vt_ represents the critical starting wind speed of sand particles at a height of 10 m, and \(V\) represents the wind speed not less than the critical starting speed of sand particles; both units are n mile-h\({}^{-1}\). \(t\) represents the duration of sand-driving wind expressed by frequency in this paper. _RDP_ (VU) and _RDD_ (\({}^{\circ}\)) are _DP_ calculations based on vector synthesis laws; _RDP_ is a vector synthesis of sand transport potential in 16 directions, reflecting net sand transport capacity. _RDD_ represents the net trend of sand transport or the overall direction of aeolian sand transport under the influence of sand-raising wind in different directions. The directional wind variability index is the ratio of _RDP_ to _DP_ (_RDP_/_DP_), used to reflect the combination of regional wind direction and the complexity of wind signals [27].  
It is of great importance to grasp the variation law of sand-drifting wind direction to explore the causes and control of sand damage [28]. The _DP_ in different seasons in the study area is shown in Figure 4 and, under the influence of seasonal winds, the highway is easily buried from different directions by sand materials with the largest _DP_ in spring (124.39 VU), followed by summer (108.97 VU) and winter (65.14 VU), and the smallest DP in autumn (64.89 VU). In the whole year, the largest Resultant Drift Potential (_RDP_) is 53.04 VU, which occurred in spring; the directional wind variability index is moderate (_RDP_/_DP_ = 0.43); and  
Figure 3: Distribution of non-directional wind speed variation (**a**) Distribution of non-directional wind speed variation (**b**) wind speed probability distribution (_Ut_ represents the starting wind speed of sand particles at 2 m height in Tengger Desert; \(U_{2}\) represents the 2 min annual observed variable wind speed in the region; \(U_{2}\) represents the 2 min average annual wind speed in the region).  
the sand drift direction is 125.92\({}^{\circ}\) so that sand materials are most easily transported from west to southeast. Following with spring, Resultant Drift Direction (_RDP_) is 53.04 VU in winter; the seasonal wind direction is single (_RDP_/_DP_ = 0.75) and the sand drift direction is 64.41\({}^{\circ}\) so that sand materials are easily transported from west to northeast. Although the sand-driving wind has a long duration and strong dust concentration in summer, the seasonal wind direction is variable (_RDP_/_DP_ = 0.38) and gale weather is frequent, accounting for the low _RDP_ (41.65 VU), final sand transport direction 162.33\({}^{\circ}\), and the fact that sand materials are easily transported from north to southeast. In autumn, with little wind and variable wind direction, _DP_ and _RDP_ are the smallest (41.65 VU) and sand drift direction is 5.73\({}^{\circ}\) so that sand materials are easily transport to the northeast. The sand transport environment in each season is in the direction of west to east. In spring, the sand drift direction and the road direction intersect almost vertically (89.08\({}^{\circ}\)), and the _DP_ and the _RDP_ are also the largest, indicating that the sand transport environment in spring is strong. As a consequence, timely attention should be paid to highway protection and sand cleaning.