Abstract
Maintenance of agricultural drainage ditches can be difficult to optimize if farmers have no guidelines on where to target their maintenance efforts. A main concern is whether ditch banks will experience soil erosion or mass movement (failure). In order to help identify sites that are more likely to experience soil erosion and/or mass movement, soil susceptibility to detachment was assessed in this study using a cohesive strength meter (CSM) and measurements of shear strength in unsaturated direct shear tests. The results showed that soil roots play an important role in stabilizing ditch banks against mass movement and in reducing the rate of soil detachment. A positive stabilizing effect was detected by CSM and confirmed by shear strength measurements. The conclusion is that native vegetation should be maintained on ditch banks, instead of being removed during maintenance work as is currently the case.
Highlights
Humans clear away natural vegetation and cultivate crops, in the process creating periodically non-vegetated areas that are prone to soil erosion [1,2,3]
Cohesive strength meter tests showed that ditch bank soils from which the vegetation had not been removed, and which had a higher density of roots, had higher resistance to detachment
Simplified slope stability analysis showed that a combination of reducing the slope of the bank and promoting development of vegetation on the bank surface stabilized the ditch bank, in some cases transforming an unstable situation into a stable situation
Summary
Humans clear away natural vegetation and cultivate crops, in the process creating periodically non-vegetated areas that are prone to soil erosion [1,2,3]. It has been shown that vegetation roots increase the shear strength of soils with high moisture content [14] and, depending on the root configuration in a channel, increase bank stability to mass movement [17] This increased stability of agricultural drainage ditches has not been assessed to date. Vegetation on the banks increases the shear strength of the soil, but is likely to reduce the forces caused by water flow in the ditch [18], decreasing its erosive force This is important because different drainage maintenance procedures affect the dynamics of vegetation present in the drainage ditch [19]. To assess the combined effect of bank slope modification and vegetation configuration, the factor of safety (FoS) for ditch banks with and without vegetation, with three different slopes and three root depths, was estimated following slope stability analysis using the finite element method
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