关键词: 敦煌莫高窟, 尼龙网栅栏, 防沙效应

Abstract: The results of field monitoring and wind tunnel experiment show that the blown sand control range of nylon net fence can be 23.5~29H width (H: the height of fence), and the sands accumulation concentrates in range of 2 H~3 H(2 H before to 3 H behind the net fence) when the porosity of the nylon grid is 20%~25%. The net fence in sandy gravel gobi can directly arrest the more than 80% sands transported by westly or southly winds, however, it has very wake side sand transportation. The sand transporting rate in outside the net fence can reach an average of 35%; that in inside the net fence are 57.5% and 15.89% under controlling eastly and westly wind, respectively, which shows the seasonal change characteristics of fencing effect. At site of 1 H behind the net fence, the velocities at 20 cm, 50 cm, 100 cm and 150 cm heights can decrease to the 48.6%, 38.6%, 40.7% and 66% respectively of the velocity at site of 3 H before net fence. The sand transport of 10 m and 2 m behind the net fence are 1/29 and 1/43, respectively, under the control of NW wind, and these ratio are also influenced by many other factors, such as the net fence layout. The fencing effect of the net fence in shifting sand area also shows difference among three wind directions. The sand-arrested effect has a close relationship with sand source supply. Sands will accumulate when with abundant of sand source; otherwise, strong erosion will occur. Comparison with no fence, the sand accumulation during March to May before the grottoes decrease 39.4%~83.3%, 75.4%~95.2% and 94.0%~98.7% respectively under no sand control in 1992, medium sand control in 2002, and well sand control in 2003. Net fence is a better material in comparison the others; it has more advantage in stopping dune migration and arresting blown sand, it is also cheap, easily constructed and capable of being re-built after being buried by sands. The local accumulated sands around the net fence could be transported by variation of seasonal winds. For controlling the sand source, measures should be adopted in the Mingsha megadune area, and then to create a passage for sand transport in the gobi area. Thus the sands should be arrested when the wind are from the west or south and returned to the Mingsha megadune by the easterly winds. For sustainable utilization, we suggest that the existing net fence system in sandy gravel gobi area should be protected and re-adjusted.

Key words: Mogao Grottoes, net fence, sand controlling effect