Temporal and spatial variability in root reinforcement of streambanks: Accounting for soil shear strength and moisture
Temporal and spatial variability in root reinforcement of streambanks: Accounting for soil shear strength and moisture
复制标题
DOI：
10.1016/j.catena.2006.05.004
复制
发表时间：
2007-04-15
期刊：
影响因子：
6.2
通讯作者：
Pollen, Natasha
中科院分区：
文献类型：
--
作者：
Pollen, Natasha
河岸植被对河岸稳定性有多种力学和水文控制作用，这会影响泥沙向河道的输送。对土壤根系加固的估算通常是使用垂直根系模型来实现的，该模型只是将根系的抗拉强度相加，并将其视为土壤强度的一个附加因素。这种垂直模型的一个主要局限是，抗拉强度和阻力被错误地认为与土壤类型和湿度无关，因此传统模型中忽略了根据这些河岸特性的变化。实际上，在河岸发生大规模坍塌时，一些根系会断裂，一些根系会完整地从土壤中拔出；根系断裂或拔出的相对比例是由土壤湿度和抗剪强度共同决定的。在本文中，针对在密西西比州朗溪两种土壤湿度条件下收集的实地数据，对一个预测根 - 土粘结摩擦力的方程进行了测试。然后将根系拔出方程纳入根系加固模型（RipRoot），并对密西西比州古德温溪进行了河岸稳定性模型运算，以研究土壤抗剪强度和根系密度的时空变化对河岸安全系数的影响。模型结果显示，在较小的根系直径下，断裂力超过拔出力，但在较大的根系直径下，拔出力超过断裂力。根系拔出和根系断裂之间的临界直径随土壤抗剪强度而变化，土壤抗剪强度增加会导致更多的根系因断裂而非拔出而失效。研究表明，根系加固估算值反映了土壤抗剪强度的变化，例如由土壤基质吸力的变化所引起的变化。在模拟期间，有1000根草根系/平方米时河岸的安全系数（F - S）值在1.36到1.74之间，相比之下，无植被河岸的安全系数值在0.97到1.37之间。研究表明，在模拟的整个土壤湿度条件范围内，根系加固都能提高河岸稳定性。然而，由土壤抗剪强度和土壤湿度决定，根系加固的程度在空间和时间上都有所不同。由爱思唯尔出版公司出版。
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 (F-S) values for the bank during the period modeled ranged from 1.36 to 1.74 with 1000 grass roots/m(2), 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. Published by Elsevier B.V.