Field measurement of basal forces generated by erosive debris flows
Field measurement of basal forces generated by erosive debris flows
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DOI：
10.1002/jgrf.20041
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发表时间：
2013-06
期刊：
影响因子：
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通讯作者：
S. McCoy;G. Tucker;J. Kean;J. Coe
中科院分区：
文献类型：
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作者：
S. McCoy;G. Tucker;J. Kean;J. Coe
有人提出，泥石流切割了世界各地陡峭地区的基岩山谷，但由于难以对自然流进行测量，限制这一过程的机械模型所需的现场测量仍然很少。在这里，我们展示并分析了使用自动传感器网络、侵蚀螺栓和安装在陡峭流域基岩河道底部的 15.24 厘米 x 15.24 厘米测力板进行的测量。这些测量使我们能够量化切割基岩的自然泥石流事件的基础力的分布。在4年的监测期内，共发生11次泥石流冲刷基岩河道底面。没有观察到清澈的水流。在研究开始和结束时对侵蚀锚杆的测量表明，基岩河道底板降低了 36 至 64 毫米。这些侵蚀性泥石流事件期间的基础力具有大幅度（高达21 kN，大约是同时期平均平均力的50倍）、高频（大于1 Hz）波动分量。我们将这些波动解释为冲击床的流动粒子。由此产生的力大小的变化随着时间平均平均基础力线性增加。基本法向力的概率密度函数符合广义帕累托分布，而不是实验和模拟单分散颗粒流中常见的指数分布，且指数分布具有较低的大力概率。当覆盖测力板的床层沉积物厚度大于床层沉积物中值粒径的 20 倍时，测量到时间平均平均力没有显着波动，这表明薄层沉积物（在监测情况下为 5 cm）可以有效地保护下面的床层免受侵蚀影响。尽管外观和体积流密度存在差异，但粗粒颗粒浪涌和富含水的中间浪涌流具有非常相似的基础力分布。这些结果表明，泥石流可以强有力地控制陡峭地的演化速率，并为泥石流切口随机建模奠定基础。
It has been proposed that debris flows cut bedrock valleys in steeplands worldwide, but field measurements needed to constrain mechanistic models of this process remain sparse due to the difficulty of instrumenting natural flows. Here we present and analyze measurements made using an automated sensor network, erosion bolts, and a 15.24 cm by 15.24 cm force plate installed in the bedrock channel floor of a steep catchment. These measurements allow us to quantify the distribution of basal forces from natural debris‐flow events that incised bedrock. Over the 4 year monitoring period, 11 debris‐flow events scoured the bedrock channel floor. No clear water flows were observed. Measurements of erosion bolts at the beginning and end of the study indicated that the bedrock channel floor was lowered by 36 to 64 mm. The basal force during these erosive debris‐flow events had a large‐magnitude (up to 21 kN, which was approximately 50 times larger than the concurrent time‐averaged mean force), high‐frequency (greater than 1 Hz) fluctuating component. We interpret these fluctuations as flow particles impacting the bed. The resulting variability in force magnitude increased linearly with the time‐averaged mean basal force. Probability density functions of basal normal forces were consistent with a generalized Pareto distribution, rather than the exponential distribution that is commonly found in experimental and simulated monodispersed granular flows and which has a lower probability of large forces. When the bed sediment thickness covering the force plate was greater than ∼ 20 times the median bed sediment grain size, no significant fluctuations about the time‐averaged mean force were measured, indicating that a thin layer of sediment (∼ 5 cm in the monitored cases) can effectively shield the subjacent bed from erosive impacts. Coarse‐grained granular surges and water‐rich, intersurge flow had very similar basal force distributions despite differences in appearance and bulk‐flow density. These results demonstrate that debris flows can have strong control on rates of steepland evolution and contribute to a foundation needed for modeling debris‐flow incision stochastically.