Effect of hydraulic shear stress on the banks of the Red River

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Goharrokhi, Masoud
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This study focuses on flow-induced bank erosion on the Red River. The study includes field measurements, experimental testing, and numerical simulation. Soil samples from the riverbank were collected at seven sites and their erodibility parameters were estimated through laboratory testing. The hydraulic shear stresses applied to the river reach were obtained by developing a 2D numerical model. Erosion rates for these sites were modeled using a linear excess shear stress equation. A bank monitoring and total suspended sediment investigation were also conducted to assess the erosion and deposition rates and patterns. The locations susceptible to erosion were determined and the periods during which these processes are likely to occur were estimated. The numerical modeling and soil testing results show that most of the time, the magnitude of flow shear stresses exerted on the bank are less than the soil sample critical shear stresses. Therefore, without considering other bank widening mechanisms as well as their interactions, the fluvial bank erosion (in isolation) should not be a significant process. However, bank monitoring shows significant bank erosion. It is recommended that the effect of subaerial processes (especially freeze-thaw) be investigated further to determine their effects on flow-induced erosion. The monitoring results convincingly show that climate-related phenomena influences cohesive soil structures and consequently, a soil’s cohesive resistance forces are significantly reduced. Therefore it can be concluded that subaerial mechanisms play a significant role in widening the banks of the Red River.
Cohesive Soil