关键词: 莫高窟顶戈壁, 风蚀危害, 砾石形状和高度, 粒径配置

Abstract: For resolving the wind erosion problem that has menaced the Dunhuang Mogao Grottos for a very long time, this paper studies the inhibiting effects of gravel mulch on wind erosion. Wind tunnel experiments and field surveys have been used to support these findings. At first, we divided the Gobi bed of Mogao Grottos districts into three zones according to the gravel cover and wind states, then took photos and some samples for examination and testing in different zones. According to analytic results of the size distribution and gravel cover density, we defined three kinds of beds as stable, semi stable and unstable. The experimental work for this paper was conducted in a straight line puff field wind tunnel in Shapotou. The tunnel was 37 m long and a 21 m long working section had a cross sectional area of 1 44 m 2 （width 1 2 m, height 1 2 m）. The test beds were located 16～20 m downwind of tunnel inlet of the working section. The Pitot tube measuring profiles of wind velocity was installed in the middle of the test bed area at the 19 8 m mark. The Pitot tube was moved along a slide to the following positions of 4, 10, 30, 50, 100, 200, 250, 300, 450 and 500 mm above the bed surface. The wind tunnel experiment consisted of two parts: （1） the relation of gravel shape, height and roughness length; （2） the characters of the particle size distribution of the stable bed surface. In the experiment, there were two kinds of wind states （with and without sand） and five kinds of wind velocity （6, 8, 10, 12 and 15 m/s）. We came to these conclusions: （1） In the same gravel cover states with low wind velocity, gravel shape affects roughness length more than gravel size, and vice versa. （2） The two basic characters of stable bed surface: >65% gravel cover and specific particle size distribution. In addition, a strong stable bed surface can inhibit erosion by the low velocity wind containing sand to some extent, but when high velocity wind containing sand goes across a bed surface, the bed surface will change from stable state to unstable state quickly. Finally, according to the findings in the Mogao Grottos Gobi and wind tunnel experiment, we suggest that: （1） for keeping the bed surface stable, it is important to cut off the source of sand and form wind without sand; （2） in the district Ⅱ, crushed gravel （>10 mm） should be paved in order to prevent strong wind erosion; due to the low wind velocity in district Ⅲ, 5～10 mm small gravel should be in higher ratio than >10 mm gravel; （3） to prevent gravel from being driven by sand salutation it is also imperative to control the particle distribution according to the appro priate standards; and （4） human activity must be control in order to keep the bed stable for a long time.

Key words: Mogao Grottos Gobi, wind erosion, shape and height of gravel, particle size distribution