Soil Erosion and Mass Movement in Agricultural Drainage DitchesAvilés, Daniel
Agricultural drainage ditches degrade over time. This degradation is often due to soil erosion, which can cause mass movement (bank failure) when the toe of the bank is eroded or the slope of the bank is too steep. Soil eroded or displaced by mass movement is either transported by the flowing water or deposited in the drainage ditch. This reduces the hydraulic capacity of the ditch creating, the need for maintenance. The efficiency of remediation measures to reduce soil erosion in agricultural drainage ditches is limited by inadequate methods to identify soils susceptible to erosion by water-induced forces and mass movement.
This thesis evaluated procedures for assessing soil susceptibility to erosion and/or mass movement. A cohesive strength meter (CSM) was used to derive an index that provides an indication of how strong a soil is to detachment compared with other soils. In addition, an approach to relate the pressures involved in a CSM test to the pressures applied on the soil surface was developed. This information could be useful for relating soil resistance to possible hydraulic pressures in the ditch. Unsaturated direct shear tests were used to determine the shear strength of soils under conditions resembling those in. the field. This information is useful for characterising the stability of ditch banks to mass movement.
The results showed that the CSM is suitable for distinguishing soils that are prone to detach easily from those that exhibit more resistance to detachment. The pressures involved in the CSM tests were found to be lower (by up to 78%) than values reported. in other studies. The shear strength of the soil, measured by unsaturated direct shear test, and the resistance to detachment, measured with the CSM, were both increased by the presence of vegetation roots. This positive stabilising effect of plant roots indicates that vegetation on agricultural ditch banks should be maintained or promoted, rather than remove it as is frequently done during maintenance work.
Keywordserodibility, cohesive strength meter, roots reinforcement, bank erosion, soil shear strength, slope stability.
Published inActa Universitatis Agriculturae Sueciae
2020, number: 2020:19
ISBN: 978-91-7760-556-0, eISBN: 978-91-7760-557-7
Publisher: Department of Soil and Environment, Swedish University of Agricultural Sciences
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