Sediment storage by vegetation in steep bedrock landscapes: Theory, experiments, and implications for postfire sediment yield
Sediment storage by vegetation in steep bedrock landscapes: Theory, experiments, and implications for postfire sediment yield
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陡峭基岩景观中植被的沉积物储存：理论、实验以及对火后沉积物产量的影响
DOI：
10.1002/jgrf.20058
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发表时间：
2013
期刊：
影响因子：
--
通讯作者：
B. Fuller
中科院分区：
文献类型：
--
作者：
M. Lamb;M. Levina;R. DiBiase;B. Fuller
从景观演化到泥石流灾害等各种应用都需要山坡沉积物输送的机制模型。土壤覆盖景观已取得进展；然而，人们对基岩景观中沉积物的产生和运输知之甚少，即使斜坡超过休止角，基岩景观通常仍保持不规则的土幔。在此，我们研究了这样的假设：由于局部粗糙度（例如捕获斜坡上沉积物的植被坝），陡坡上的斑块土壤覆盖是稳定的。为了量化当地沉积物储存量，我们开发了一种新理论，并通过倾斜台实验对其进行了测试。结果表明，截留的沉积物体积与大坝宽度的三次方成正比。在坝宽小于约 50 个颗粒直径的情况下，颗粒力链似乎增强了稳定性，导致更大的截留体积和超过休止角的沉积物堆坡度。对于刚刚超过摩擦坡度的山坡，截留体积最大，并且对于大于摩擦坡度约两倍的坡度，截留体积与山坡坡度无关。对于间隔小于约五个颗粒直径的相邻水坝，颗粒桥接会导致单个沉积物堆比单个沉积物堆的总和还要大。这项工作为量化基岩景观中的沉积物储存和非局域运输提供了一个质量守恒框架。结果可以解释在没有降雨的情况下，在陡峭地形上发生野火后沉积物产量迅速增加的原因；当沉积物坝被焚烧时，颗粒在重力作用下变得不稳定，并以干燥散布的形式迅速下坡。
Mechanistic models for sediment transport on hillslopes are needed for applications ranging from landscape evolution to debris‐flow hazards. Progress has been made for soil‐mantled landscapes; however, little is known about sediment production and transport in bedrock landscapes that often maintain a patchy soil mantle, even though slopes exceed the angle of repose. Herein we investigate the hypothesis that patchy soil cover is stable on steep slopes due to local roughness such as vegetation dams that trap sediment upslope. To quantify local sediment storage, we developed a new theory and tested it against tilt‐table experiments. Results show that trapped sediment volume scales with the cube of dam width. Where the dam width is less than about fifty grain diameters, particle force chains appear to enhance stability, resulting in greater trapped volumes and sediment‐pile slopes that exceed the angle of repose. Trapped volumes are greatest for hillslopes that just exceed the friction slope and are independent of hillslope gradient for gradients greater than about twice the friction slope. For neighboring dams spaced less than about five grain diameters apart, grain bridging results in a single sediment pile that is larger than the sum of individual piles. This work provides a mass‐conserving framework for quantifying sediment storage and nonlocal transport in bedrock landscapes. Results may explain the rapid increase in sediment yield following wildfire in steep terrain in the absence of rainfall; as sediment dams are incinerated, particles become gravitationally unstable and move rapidly downslope as dry ravel.