Headcut erosive regimes influenced by groundwater on disturbed agricultural soils.
Headcut erosive regimes influenced by groundwater on disturbed agricultural soils.
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DOI：
10.1016/j.jenvman.2009.08.021
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发表时间：
2011-02
影响因子：
8.7
通讯作者：
D. Rockwell
中科院分区：
文献类型：
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作者：
D. Rockwell
一系列模拟降雨实验，在 10m×0.8m 实验室水槽中测试了多种土壤和坡度，显示出 10cm 深度地下水位的初始发育与高度侵蚀性切头形成之间的密切相关性。在某些土壤和坡度上，在最初地下水位上升的几分钟或几秒钟内，高度侵蚀性的断面会持续且可预测地形成。然而，仅靠砍头并不是侵蚀加剧的良好指标。在大多数实验中，一些头切口很早就形成，通常是在地表水力参数值达到既定的细沟萌生阈值时形成，但导致侵蚀增加很少或没有。后来，在最初的地下水位上升时，其他断头的形成与主要侵蚀增加同时发生，通常地表水力值小于细沟萌生阈值。在所测试的四种土壤中，除了 9° 的陡坡外，如果不开发地下水，就不会形成高度侵蚀的断头。诸如断头形态和断头推进率等常见视觉指标并不是确定侵蚀或地下水存在的有效手段。只有使用微型立管和 TDR 对地下湿度条件进行局部监测才能帮助确定顶头切割过程和侵蚀状况。受地下水影响的头切形成可能是由土壤孔隙水压力增加和地表雨流中土壤剪切强度降低引起的，而不是由土壤基质的侵蚀或渗漏引起的。因此，在常见的农业条件下，在地表附近存在渗透性降低的情况（例如犁盘）时，可能会形成高度侵蚀性的头切口，而无需饱和土壤。切头侵蚀状况也受到土壤类型和坡度的显着影响，其中地下水对中等坡度和相当渗透性土壤的影响最大。
A series of simulated rainfall experiments, testing several soils and slope gradients in a 10m×0.8m laboratory flume, displayed close correlations between initial development of a water table at a 10cm depth and highly erosive headcut formation. On some soils and gradients, highly erosive headcuts formed consistently and predictably within minutes or seconds of initial water table rise. However, headcuts alone were not good indicators of increased erosion. In most experiments some headcuts formed early, often when surface hydraulic parameter values reached established rill initiation thresholds, but resulted in little or no erosion increase. Later, at initial water table rise, other headcuts formed coincident with major erosion increase, often with surface hydraulic values then less than rill initiation thresholds. On the four soils tested, highly erosive headcuts never formed without groundwater development, except on steep 9° slopes. Common visual indicators such as headcut morphology and headcut advance rates were not effective means of determining either erosion or the existence of groundwater. Only local monitoring of subsurface moisture conditions with micro-standpipes and TDR aided in determining headcut processes and erosive regimes. Groundwater-influenced headcut formation was likely caused by increased soil pore-water pressures and decreased soil shear strengths in surface rainflow, not by sapping or seepage from the soil matrix. Highly erosive headcuts can thus form under common agricultural conditions where reductions in permeability, such as plow pans, exist near the surface – without the need for saturated soils. Headcut erosive regimes were also significantly influenced by soil type and slope gradient, with the greatest effects of groundwater on moderate slopes and fairly permeable soils.