土壤含水率及物理性砂粒含量对风蚀模数影响的风洞模拟

为了探究土壤含水率及物理性砂粒含量对土壤风蚀模数的影响,在室内风洞中在5、6、9、12、15和18m/s风速下对不同含水率(0,1%,2%,3%,4%,5%,6%,7%,8%,9%和10%)的7种土壤(物理性砂粒质量分数的分别为20%、30%、40%、50%、60%、70%和80%)进行了10min吹蚀,在风洞轴线距出口1.2m处放置旋风式集沙仪分别测定垂直方向上10个不同高度的风蚀物收集量(高度分别为20、60、120、180、240、300、400、500、600和700mm),并利用MATLAB7.4.0(R2007)软件采用3次样条插值拟合法对旋风式集沙仪不同高度的风蚀物收集量进行积分,通过换算计算土壤风蚀模数E。结果表明,物理性砂粒质量分数低于40%的土壤在各种水分条件下集沙仪不同高度风蚀物收集量均很小。物理性砂粒质量分数≤20%时,风蚀物收集量在空间上符合指数函数变化规律;20%<物理性砂粒质量分数<40%风蚀物收集量在空间上利用指数函数和幂函数拟合相关性均很好,物理性砂粒质量分数高于40%后,风蚀物收集量在空间上呈现幂函数曲线变化规律。9m/s风速基本上是风蚀物空间动态发生变化的临界点;低于临界风速,风蚀物收集量与高度符合指数曲线变化规律;高于临界风速,二者符合幂函数曲线变化规律。集沙仪不同高度的总输沙量随风速的增加而增大,二者符合指数曲线变化关系。物理性砂粒质量分数低于40%的土壤,不会有风蚀现象发生;当物理性砂粒质量分数大于40%后,土壤容易发生风蚀,而且风蚀程度随物理性砂粒含量的增加而增大,尤其当土壤含水率低于3%时,极易发生风蚀。风速越大土壤风蚀模数越大,风蚀模数与风速按照指数曲线规律进行变化。阴山北麓旱作区冬春季节土壤地表含水率一般维持在3%～4%,土壤的物理性砂粒质量分数基本在50%～80%;单纯从土壤水分和土壤物理性砂粒含量考虑,阴山北麓旱作区大部分地区是沙尘暴的发生源。

Effects of soil moisture and physical sand content on wind erosion modulus in wind tunnel testing

In order to explore the effects of soil moisture and physical sand contents on wind erosion modulus, seven artificial soil type treatments with physical sand contents of 20 %, 30 %, 40 %, 50 %, 60 % and 70 %, eleven treatments with soil moisture contents from 0 to 10 % at 1 % a step, and six wind speed treatments with 5, 6, 9, 12, 15 and 18 m/s, were tested in a instrument of wind erosion tunnel. The wind erosion amount was measured after 10 min wind blowing at 10 different heights of 20, 60, 120, 180, 240, 300, 400, 500, 600 and 700 mm with a cyclone sand collector, which set at placements of 1.2 m away from the wind tunnel. The results were integrated by using cubic spline interpolation method in MATLAB 7.4.0 (R2007) and were computed to wind erosion modulus E. The results showed that the wind erosion amount was very small when the sand content was less than 40%, showed no significant effects for water contents and collecting heights. The amount of wind erosion collected fitted a exponential function at spatial scale when physical sand quality fraction was smaller than 20%, it well fitted both exponential or power functions when physical sand quality fraction was ranged between 20% to 40%, and it fitted a power function when the sand content was higher than 40%. The wind erosion showed an exponential increase against the heights when the wind speed was slower than 9 m/s, and changed to a power function when it was faster than 9 m/s. The total amount of wind erosion in collectors at different heights was exponentially increased with the wind speeds. There were no significant difference in wind erosion accured when the sand content less than 40%. When sand content increased to more than 40%, the wind erosion increased along with increasing sand contents, especially when the soil moisture content was lower than 3%. The E showed an exponential increase against wind speeds. We concluded that the north side region of Yinshan Mountain, Inner Mongolia, China would be an important source of sandstorm with considering the soil moisture contents and physical sand contents, because the soil moisture content, in this region, was often less than 3% to 4 % in spring and winter seasons, the sand contents were more than 50% to 80%.