Hydrologic and hydraulic effects of riparian root networks on streambank stability: is mechanical root-reinforcement the whole story?
Hydrologic and hydraulic effects of riparian root networks on streambank stability: is mechanical root-reinforcement the whole story?
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DOI：
10.1016/j.geomorph.2009.11.013
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发表时间：
2010-04
期刊：
影响因子：
3.9
通讯作者：
N. Pollen-Bankhead;A. Simon
中科院分区：
文献类型：
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作者：
N. Pollen-Bankhead;A. Simon
河岸植被对河岸破坏机制有许多影响，有些是积极的，有些是消极的。以往的研究表明，机械根系加固对土壤稳定性的影响是相当大的，可以成功地量化，并包括在河岸稳定性模型。然而，土壤基质中的根系网络对作用于河岸的水文和水力过程也有影响，尽管这些影响经常被讨论，但通常难以量化。本文总结了现场数据收集，实验室测试和计算机模拟的结果进行更好地量化河岸植被对水文和水力过程发生沿着河岸。首先，不同的河岸物种的蒸散潜力被隔离，通过建立一个实验，生长年轻的河岸树木和开关草在单独的土柱，每个仪器与张力计在30厘米和70厘米的深度，并与裸对照列进行比较。水文加固提供给土壤增加表观凝聚力的结果，增强基质吸力的范围估计为1.0至3.1kPa的春季时，银行的稳定性是最关键的，在夏季达到最大值5.0kPa。其次，采用垂直射流试验装置，测定了柳枝草根渗透土壤的冲刷速率和冲刷量。结果表明，土壤冲刷量随单位体积土壤根系体积、根长密度和根系生物量的增加呈非线性下降。相对土壤剥离率（RSD）的计算结果表明，最高的生根密度在现场喷射试验中测得的，侵蚀土壤体积的10%，在没有根的测试。第三，使用BSTEM 5.1模拟了蒸散引起的基质吸力增强以及植物根系的存在导致土壤可蚀性降低的影响，以量化对河岸安全系数（FS）的影响，并与机械根系加固的效果进行比较。敏感性分析表明，蒸发蒸腾的土壤基质吸力的变化提供了最大的潜在利益FS，但只有在夏季。在冬季和春季，根加固仍然是最重要的贡献者FS。这里进行的敏感性分析还表明，虽然根能够减少水力冲刷的体积，对河岸几何形状产生的影响并没有增加Fas多的土壤基质吸力和/或机械根加固的变化。
Riparian vegetation has a number of effects on the mechanisms by which streambanks fail, some positive and some negative. Previous research has shown that the effect of mechanical root-reinforcement on soil stability can be considerable, and can be successfully quantified and included in streambank stability models. Root networks contained within a soil-matrix, however, also have effects on the hydrologic and hydraulic processes acting on a streambank, and although these effects are often discussed they have generally been difficult to quantify. This paper summarizes the results of field data collection, laboratory testing and computer simulations carried out to better quantify the effects of riparian vegetation on hydrologic and hydraulic processes occurring along streambanks. First, the evapotranspiration potentials of different riparian species were isolated by setting up an experiment to grow young riparian trees and switch grass in separate soil columns, each instrumented with tensiometers at 30cm and 70cm depths, and compared against bare control columns. The hydrological reinforcement provided to the soil from increased apparent cohesion as a result of enhanced matric suction was estimated to range from 1.0 to 3.1kPa in spring when bank stability was most critical and up to a maximum of 5.0kPa in the summer. Second, a vertical jet-test device was used to measure rates and volumes of scour in soils permeated by switch grass roots. Results showed that the volume of soil scoured during a test declined non-linearly with increasing root volume, per unit volume of soil, and with increasing root length density (RLD) and increasing root biomass. Calculation of relative soil detachment rates (RSD) showed that with the highest rooting densities measured in the field jet-tests, eroded soil volume was 10% of that in the tests with no roots. Third, the effects of enhanced matric suction from evapotranspiration, and decreased soil erodibility because of the presence of plant roots were modeled using BSTEM 5.1 to quantify the effects on streambank factor of safety (Fs), and to compare with the effects of mechanical root-reinforcement. The sensitivity analysis showed that the change in soil matric suction from evapotranspiration provided the greatest potential benefit to Fsbut only during the summer months. During the winter and spring months, root-reinforcement remained the most important contributor to Fs. The sensitivity analysis conducted here also showed that whilst roots are capable of reducing the volume of hydraulic scour, the resulting effect on streambank geometry did not increase Fsas much as changes in soil matric suction and/or mechanical root-reinforcement.