Reporting a Case Study on Computational Fluid Dynamics (CFD) Modelling to Estimate Fluvial Bank Erosion

Models of river bank erosion are an important prerequisite for understanding the creation of river meanders and for estimating the possible loss of land and the potential risk to infrastructure in the floodplain. While bank erosion models considering large-scale mass collapse have been established, the contribution of fluvial erosion (the particle-by-particle erosion mechanism due to the shear action of the river flow) to bank retreat has not received as much attention. In theory, these rates of fluvial bank erosion can be quantified using formulations of excess shear stress, but it has proven difficult in practise to estimate the parameters involved. In this research, a series of three-dimensional Computational Fluid Dynamics ( CFD) simulations were performed at Bridport in southern England for a meander loop on the River Asker (200 m long) in order to elucidate the overall flow structures and in particular to provide estimates of the fluid shear stress applied to the riverbanks. The models for the CFD, Discharge flow varies. At maximum bank, the velocity levels and simulated shear stresses inside the separation zones of the inner bank are shown to be higher than those observed under low flow conditions, and these elevated shear stresses may be necessary to extract accumulated sediments into the main downstream flow. Spread and combine regions of higher bed / bank shear stress, while recirculation regions and areas of relatively small bed / bank shear stress decrease in magnitude. Compared to those simulated at low flow, the degree of velocity and shear stresses over the areas of inner bank separation was found to be greater at high flow, and may be sufficient to prevent sediment movement into the main downstream flow. These modelled flow patterns have implications for the dynamics of sediments, bank erosion and migration of meanders in the range studied.

Author (s) Details

Emmanouil Spyropoulos
Saudi Aramco, Dhahran, Kingdom of Saudi Arabia.

Professor Stephen E. Darby
School of Geography and Environmental Sciences, University of Southampton, Southampton, United Kingdom.

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