崩岗崩积体坡面产沙与坡面形态的耦合影响

Coupling Effects of Sediment Yield with the Erosion Slope Morphology of the Colluvial Deposits of Benggang

为了探究崩岗崩积体长时间序列的侵蚀变化,在崩积体典型坡度(30°)及研究区强降雨(3.33mm/min)条件下,进行了持续20场次降雨的崩积体侵蚀过程模拟试验。结果表明,在本试验条件下降雨溅蚀和径流冲刷对崩积体产沙的平均贡献率分别为47.6%和52.4%,在崩积体侵蚀过程中,其产沙量呈幂函数减小;弗劳德数、径流功率、达西-韦斯巴赫阻力系数与崩积体产沙量具有较好的相关关系,在沙源充足时,其参数可用于定量描述坡面径流产沙效能;崩积体侵蚀过程可分为4个阶段:(1)含沙量为0.099kg/L,以片蚀为主,坡面未见粗化;(2)含沙量为0.052~0.101kg/L,以细沟侵蚀为主,坡面粗化不明显;(3)含沙量为0.011~0.064kg/L,以细沟侵蚀为主,坡面粗化显现;(4)含沙量为0.008~0.036kg/L,无明显的主导侵蚀方式,坡面持续粗化。降雨及其径流对崩积体的分选性搬运,致使崩积体坡面粗化,而崩积体坡面粗化,反过来又使得降雨及其径流产沙效能降低。

In order to explore long term evolution of soil erosion from Benggang-derived sediment deposits,indoor simulated rainfall experiment was conducted with a 30°slope of the Benggang deposit and rainfall erosion intensity of 3.33 mm/min,which represented a typically higher rain intensity in the study region.The experiment was repeated with 20 times and the erosion processes of the deposit was carefully recorded.Under the experimental conditions,the average contribution rate of rainfall splash and runoff flush to sediment yield was 47.6% and 52.4%,respectively.The sediment yield of colluvial deposits decreased exponentially in the process of erosion.The sediment yield was correlated with Froude number,runoff power and Darcy-weisbach resistance coefficient,and these parameters could be used to quantitatively describe the efficiency of runoff sediment yield when the source of sediment was sufficient.Four stages of the erosion process from the colluvial deposits were founded,including（1）sheet erosion stage on the whole slope,the sediment concentration was 0.099 kg/L,and the sheet erosion was dominant,but the slope surface was not coarsening;（2）Initial formation stage of rill erosion,the sediment concentration was from 0.052 to 0.101 kg/L,mainly with rill erosion,but the slope coarsening was not obvious;（3）Stage of frequent expansion of rills with coarse slope,the sediment concentration was from 0.011 to 0.064 kg/L,mainly with rill erosion,and the coarsening of slope surface appeared;（4）The stage with frequent collapsed rills even forming ephemeral gully,the sediment concentration was from 0.008 to 0.036 kg/L,and there was no obvious dominant erosion mode,and the slope surface continued to coarsening.The separation and transportation of colluvial deposits by rainfall and its runoff results in the coarsening of the slope,and the coarsening of the slope,which in turn reduced the rainfall and runoff sediment yield.