乌兰布和沙区风沙运移特征分析

Sand flow characteristics in Ulan Buh Desert

在国家林业局磴口荒漠生态站长期监测基础上,通过野外实时输沙观测,对乌兰布和沙区地表风沙活动特征进行了分析,结果表明：（1）乌兰布和沙区主害风向为NW-WNW,占全年起沙风频率的53.56%,起沙风以7~9 m·s^-1为主,占全年起沙风频率的67.64%;3~4月、11~12月风沙活动最为强烈,分别占全年起沙风持续时间的33.78%和25.36%;（2）风沙流主要由0.25~0.05 mm细沙和极细沙构成,100 cm高度范围内,输沙总量的70.7%分布在10 cm高度内,90.0%分布在30 cm高度内,随高度增加,输沙率呈负幂函数规律衰减,由此可见,该地区的风沙活动主要集中在近地面30 cm高度范围内;（3）理论上,跃移输沙的空间分布与起沙风风向频率分布应基本一致,差异主要由各方位风的强度及持续时间等因素导致。研究结果可为该区域防沙工程设计提供理论参考。

The damage of sand flow is multi-aspect, not only its destruction to soil surface texture and weakening to anti-erodibility of soil, but also its impacts on air quality and human activities. Ulan Buh Desert is one of the eight largest deserts in China, located at the desert steppe to stepped desert transition zone. It is not only one of the main source areas and the main paths of dust storms in northern China, but also the most seriously desertificated area in China. Sand flow section which Ulan Buh Desert directly harms the Yellow River is more than 20 km, and the sand transport to Yellow River is about 7.72 × 10^7 kg every year, which accounted for 37% of the Yellow River sand con- centration. Situation of desertification in the region and the occurrence of dust storms has brought great harm to local economy and social development. So, it is of great significance to study moving laws of surface layer sand flow. On the basis of long-term monitoring of the Dengkou Desert Ecosystem Station of State Forestry Administration, the sand flow was studied in the Ulan Buh Desert. The results show as follows ： （ 1 ）In Ulan Buh Desert, the main wind di- rection is NW-WNW, and it takes about 53.56% of sand wind frequency all year, sand wind takes about 67.64% of sand wind frequency and the sand driving wind is mainly concentrated on 7-9 m· s^-1 ; aeolian sand activities were more stronger in March-April and November- December, which take about 33.78% and 25.36% of annual sand driving wind duration. （2） Sand flow is constituted by the 0.25-0.05 mm sand and very fine sand. Over 70.7% of the total sand-transporting volume near land surface is distributed within the height of 10 cm, and 90.0% is distributed within the height of 30 cm, which means that the aeolian sand activities in Ulan Buh area is mainly in height of 30 cm above ground surface. The sand discharge rate decreases with height increase according to negative power func- tion. The absolute sand discharge rate increases with the strengthening of wind speed, and the surface wind erosion get worse; the relative sand discharge rate tends to decrease at surface layer（0-4 cm）, slightly change at middle layer （4-30 cm）, increase at upper layer（30-100 cm）. The average particle size of sand has obvious decreasing trend with increase of height, the smaller the particle size the higher of the sand particle jumps. （3） In theory, the spatial distribution of sand saltation is basically consistent with the distribution of wind direction frequency, the difference primarily result from the factors like the intensity of orientated wind and the wind duration. The results can provide theoretical reference for the regional sand flow control engineering design.