Zhishan An

Quantitative analysis on the dynamic characteristics of megadunes around the Crescent Moon Spring, China

The Crescent Moon Spring is a precious natural heritage. However, the dynamic characteristics of megadunes around the Crescent Moon Spring are not well known. This paper quantitatively studied the characteristics and changes of megadunes around the Crescent Moon Spring by interpreting aerial photographs taken in 1985 and 2004 and analysing the dune crestlines and the wind data collected from 2011 to 2012. Results revealed that pyramid dunes were formed by a complex wind regime. The Crescent Moon Spring was not buried by shifting sands because of the stable wind regime and relative stability of pyramid dunes. The crestlines of the dunes around the spring moved northward between 1985 and 2004. The south-facing slip faces were also exposed to wind erosion, whereas the other faces were under deposition, thus indicating that the southerly wind was relatively enhanced. Limiting the scale of tall windbreaks and architectures in the Dunhuang oasis at the north of the spring was necessary to maintain the dynamic equilibrium of the wind regime and sand transport.

Effects of gravel mulch on aeolian transport: a field wind tunnel simulation

The shape, size and coverage of gravels have significant impacts on aeolian sand transport. This study provided an understanding of aeolian transport over the gravel mulching surfaces at different wind velocities by means of a mobile wind tunnel simulation. The tested gravel coverage increased from 5% to 80%, with a progressive increment of 5%. The gravels used in the experiments have three sizes in diameter. Wind velocities were measured using 10 sand-proof pitot-static probes, and mean velocity fields were obtained and discussed. The results showed that mean velocity fields obtained over different gravel mulches were similar. The analysis of wind speed patterns revealed an inherent link between gravel mulches and mean airflow characteristics on the gravel surfaces. The optimal gravel coverage is considered to be the critical level above or below which aeolian transport characteristics differ strongly. According to the present study, the optimal gravel coverage was found to be around 30% or 40%. Threshold velocity linearly increased with gravel coverage. Sand transport rate first increased with height above the wind tunnel floor (Hf), reaching a peak at some midpoint, and then decreased.

Dune dynamics in the southern edge of Dunhuang Oasis and implications for the oasis protection

The survival of Dunhuang Oasis is largely determined by the evolution of sand dunes in the southern edge of the oasis, mainly composed of shield dunes and mega pyramid dunes, which occupy two-thirds and one-third of the area, respectively. However, few studies have focused on dynamics of these dunes, especially in terms of quantification. So the theoretical basis of sand-control engineering is relatively limited. Here we present the characteristics of dune dynamics of a shield dune and mega pyramid dune in the southern edge of Dunhuang Oasis during April 2014–April 2016 based on measurement data of a 3-D laser scanner. Results indicate that the volume of the shield dune decreased during the monitoring period of two years, and the gravity centers of the monitored shield dune moved windward, indicating that sand was transported toward the oasis. Conversely, the dune volume of the mega pyramid dune increased and the gravity center presented no prominent movement, indicating that the mega pyramid dune was relatively stable and its migration toward the oasis was not notable. Thus, compared with mega pyramid dunes, shield dunes in the southern edge of Dunhuang Oasis are identified as a more significant sand source endangering the protection of the oasis, and sand-control engineering should mainly focus on these shield dunes.

Local Circulation Maintains the Coexistence of Lake-dune Pattern in the Badain Jaran Desert

Previous studies proposed various hypotheses to the formation of the mega-dunes and water recharge of the lakes in the Badain Jaran Desert but left the coexistence of lake-dune pattern unsolved. This research found that the local circulation, generated from the differences of thermodynamic properties and the unique landscape settings between lakes and mega-dunes, can be applied to interpret the pattern.