首页> 外文期刊>Catena: An Interdisciplinary Journal of Soil Science Hydrology-Geomorphology Focusing on Geoecology and Landscape Evolution >Temporal and spatial variability in root reinforcement of streambanks: Accounting for soil shear strength and moisture
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Temporal and spatial variability in root reinforcement of streambanks: Accounting for soil shear strength and moisture

机译:防洪堤根部加固的时空变化:考虑土壤抗剪强度和湿度

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摘要

Riparian vegetation exerts a number of mechanical and hydrologic controls on bank stability, which can affect the delivery of sediment to channels. Estimates of root reinforcement of soils have commonly been attained using perpendicular root models that simply sum root tensile strengths and consider these as an add-on factor to soil strength. A major limitation of such perpendicular models is that tensile strength and resistance is wrongly considered to be independent of soil type and moisture, and therefore variations according to these bank properties are omitted in conventional models. In reality, during mass failure of a streambank, some roots break, and some roots are pulled out of the soil intact; the relative proportions of roots that break or pull out are determined by a combination of soil moisture and shear strength. In this paper an equation to predict the frictional resistance of root-soil bonds was tested against field data collected at Long Creek, MS, under two soil moisture conditions. The root pullout equations were then included in the root-reinforcement model, RipRoot, and bank stability model runs for Goodwin Creek, MS, were carried out in order to examine the effects of spatial and temporal variations in soil shear strength and rooting density, on streambank factor of safety. Model results showed that at smaller root diameters breaking forces exceeded pullout forces, but at larger root diameters pullout forces exceed breaking forces. The threshold diameter between root pullout and root breaking varied with soil shear strength, with increasing soil shear strength leading to a greater proportion of roots failing by breaking instead of pullout. Root-reinforcement estimates were shown to reflect changes in soil shear strength, for example, brought about by variations in soil matric suction. Resulting Factor of safety (FS) values for the bank during the period modeled ranged from 1.36 to 1.74 with 1000 grass roots/m2, compared to a range of 0.97 to 1.37 for the non-vegetated bank. Root reinforcement was shown to increase bank stability under the entire range of soil moisture conditions modeled. However, the magnitude of root reinforcement varied in both space and time as determined by soil shear strength and soil moisture.
机译:河岸植被对河岸的稳定性施加了许多机械和水文控制,可能会影响沉积物向河道的输送。通常使用垂直的根模型对土壤的根系增强进行估算,该模型简单地将根的抗张强度求和,并将其视为土壤强度的附加因子。这种垂直模型的主要局限性是错误地认为抗张强度和抗力与土壤类型和水分无关,​​因此在常规模型中忽略了根据这些堤岸特性的变化。实际上,在河堤的大面积破坏期间,一些根系断裂,一些根系原封不动地从土壤中拔出。根部折断或拔出的相对比例取决于土壤水分和抗剪强度。本文针对在两种土壤水分条件下在密西根州长溪市收集的田间数据测试了预测根-土键的摩擦阻力的方程式。然后,将根拔出方程包括在根加固模型RipRoot中,并针对MS的Goodwin Creek进行了堤岸稳定性模型运行,以检验时空变化对土壤抗剪强度和生根密度的影响。河岸安全系数。模型结果表明,在较小的根部直径下,拉拔力超过拉拔力,但在较大的根部直径下,拉拔力超过拉拔力。根部拔出和断根之间的阈值直径随土壤抗剪强度而变化,随着土壤抗剪强度的增加,更大比例的根部因断裂而不是拔出而断裂。根加固估计值显示出土壤抗剪强度的变化,例如,土壤基质吸力的变化所引起的变化。在建模期间,堤岸的安全系数(FS)值范围为1.36至1.74,基层为1000个/ m2,而无植被堤岸的安全系数为0.97至1.37。在整个模拟的土壤水分条件下,根部加固显示可以增加河岸的稳定性。但是,根系增强的大小在空间和时间上都变化,这取决于土壤的抗剪强度和土壤湿度。

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