不同砾石覆盖度戈壁床面风蚀速率定量模拟

通过风洞实验,利用称重传感器自动记录风蚀观测样方重量变化过程,对供沙条件下不同砾石覆盖度戈壁床面风蚀速率进行了定量模拟研究。结果表明:砾石覆盖度是影响戈壁风蚀速率的关键因子,戈壁床面风蚀速率随砾石覆盖度增加按指数规律递减。各实验风速下,砾石覆盖度>50%时,戈壁床面风蚀速率随砾石覆盖度增加而减小量有限,甚至无风蚀发生;而盖度从10%到50%时,风蚀速率显著减小。因此,两种实验粒径砾石(3 cm与4 cm)至少在50%盖度时才能达到较好的风蚀防治效果。戈壁风蚀防护机理主要是砾石覆盖度的增加增大了砾石间沙粒的临界起动剪切风速,而且减少了作用在砾石间可蚀地表的剪切压。与沙质对照床面相比,10%~90%砾石盖度戈壁床面沙粒临界起动剪切风速增大了0.8~3.4倍,只有0.5％~28%的剪切压作用在砾石间可蚀地表。

Quantitative Simulation of Erosion Rates of Gobi with Different Gravel Coverages

Wind tunnel tests were conducted to quantitatively simulate the erosion rates of gobi beds with different gravel coverages under sand supply by using weighing sensor and measuring the weight change of the erosion quadrat. Results reveal that gravel coverage is an important factor influencing erosion rates of gobi, and erosion rates decrease exponentially with increasing gravel coverage. When gravel coverage is over 50%, erosion rates decrease slowly with increasing gravel coverage and even no erosion occurring, indicating that the improvement in the protective effect against wind erosion is limited as increasing gravel coverage from 50% to 90%. However, erosion rates decrease markedly as gravel coverage increases from 10% to 50%. Thus, gobi beds composed of 3 and 4 cm gravels have good protective effect against wind erosion as gravel coverage at least reaches 50%. The protective effect of gobi beds against wind erosion can be explained by their effect on the threshold friction velocity for sand movement and shear stress partitioned into the erodible surface between gravels. Experimental results reveal that the threshold friction velocity for sand movement increases with increasing gravel coverage, and compared with the same sandy surface without covering gravels, it increases by 0.8-3.4 times, and only 0.5%-28% of the total shear stress is partitioned into the erodible surface as gravel coverage changes from 10% to 90%. This study has important referential significance for the application of the sand drift control engineering of gravel mulch to wind erosion control.