风沙流输沙通量垂向分布研究 ——以塔克拉玛干沙漠南缘流沙地表风沙流观测为例

 于2010年4—6月在塔克拉玛干沙漠南缘策勒绿洲外缘流沙地进行风速、风向和输沙量同步观测,利用观测到的28组数据对输沙通量的垂向分布进行研究。结果表明,在4.5～8 m·s-1的风速区间内,总输沙率随风速增长速率较慢,大于8  m·s-1时增长迅速。在较小风速时,4个高度层(1 cm、3 cm、9 cm和19 cm)的输沙比率变化不明显,当风速大于6.6 m·s-1时,1 cm和19 cm高度输沙比率的调整较为明显,前者减小而后者增加,中间两层(3 cm、9 cm)则维持一定波动。不同的蚀积条件对于输沙通量的垂向分布具有一定的影响,平均跃移高度则在一定程度上反映了地表沙粒的吹蚀和堆积过程。在4种常见的描述输沙通量垂向分布的模型中,Zingg的修正幂函数具有最好的拟合程度,但反映的风沙流信息最少,简单幂函数的参数包涵了最为丰富的风沙流信息但拟合程度最差,指数函数同时具有较好的拟合程度和参数意义,Fryrear的幂函数则与指数函数恰恰相反。在沙物质以极细沙为主的塔克拉玛干沙漠南缘,指数函数较之简单幂函数能更好地描述该区域输沙通量的垂向分布,验证并补充了风洞实验的结果。综合比较认为,指数函数能更好地描述塔克拉玛干沙漠南缘输沙通量的垂向分布。

Vertical Distribution of Aeolian Sand Mass Flux based on Field Observation at Southern Rim of the Taklimakan Desert

Sand transport flux,wind speed and wind direction were observed simultaneously on bare sand surface at the southern rim of the Taklimakan Desert from April to June in 2010.Vertical distribution of sand transport flux was studied with the 28 groups of observed data.Results showed that total transport rate increased slowly when wind velocity ranged from 4.5 m·s-1 to 8 m·s-1 and increased sharply when wind velocity was higher than 8.0 m·s-1.The percentage of transport rate varied unnoticeably at lower wind velocities at the four examined layers(1 cm,3 cm,9 cm and 19 cm),but when wind velocity was higher than 6.6 m·s-1,the percentage of transport rate decreased at the lowest layer(1 cm) while increased at the highest layer(19 cm),yet it still remained unnoticeable variety at the other two layers(3 cm and 9 cm).The processes of surface erosion and sediment deposition had effect on vertical distribution of sand flux,and average saltation height reflected characteristics of these aeolian processes to some extent.Of the four frequently used models that described vertical distribution of sand flux,Zingg’s modified power model produced the best fitness but the least message related to sand flow in its fitting parameters;the basic exponential model possessed the most message related to sand flow but the worst fitness;the exponential model took on a relatively good performance on both fitness and physical significance of parameters while Fryrear’s modified power model was reverse.At the fine sand dominated south margin of the Taklimakan Desert,the exponential model presented better fitness than the basic power model,and validated and enriched the conclusion that was drawn from wind tunnel experiment.Based on comprehensive comparison,the exponential model was considered to be the best one to describe vertical distribution of sand flux at the southern rim of the Taklimakan Desert.