Abstract
Physically based numerical models can predict scour depth at embankments located in bend reaches. However, methodologies for utilizing these numerical models to assess the risk of reinforced concrete embankment failure are rarely investigated. Therefore, a new assessment methodology is proposed to predict the riverbank failure caused by bend scour. The methodology is primarily based on a bend scour simulation model that integrates a one-dimensional (1D) hydraulic model, a two-dimensional (2D) hydrodynamic finite-volume model, and an empirical equation of bend scour prediction. The model was first applied to the Shuiwei Embankment located in a river bend reach of Da-An River in Taiwan and verified against results from the 1D hydraulic model and field data. The model was then used to simulate 2D flow field and the temporal evolution of bend scour depth under different return period flood events to examine the relationships between river discharge, water level, shear stress, and bend scour depth. The influence of shear stress on the stability of toe protections was also investigated. The field data (from two events) and numerical solutions (four scenarios) were assessed to conceive two empirical equations for predicting shear stress and bend scour depth. A new assessment methodology was proposed using these two equations to predict the risk of river embankment failure during flood periods. The proposed methodology can be easily applied in other disaster-prone regions to mitigate the effects of disasters caused by bend scouring.
Highlights
The principal purpose of river embankments is to reduce flood risk and protect properties.Taiwan is located in the Pacific Ocean and is struck by three to four typhoons per year on average.Typhoon-induced floods frequently cause disasters
The linking procedure is conducted in the following steps: (a) The WASH1D model for unsteady river flow is employed at the stream section scale to simulate the flow parameters as input data for 2D bend scour modeling at the river structure far-field scale, (b) the SFM2D model is employed to predict the flow velocity and water depth near the river structure, and (c) the collected results values are input into the empirical equation to predict the temporal evolution of the localized scour depth
The results reveal that the simulated value of shear stress at the Shuiwei Embankment under peak-flood condition is 345.91 N/m2, which is smaller than the critical value of 588.6 N/m2 [47]
Summary
The principal purpose of river embankments is to reduce flood risk and protect properties. Huang et al [9,10] employed a limit equilibrium method to assess river embankment stability in southern Taiwan for various flood return periods In their adopted method, three failure mechanisms can be studied: overtopping, levee foundation scouring, and slope sliding. The simulation method by Guo et al [19] will be extended to link with 1D model for predicting river embankment failure caused by toe scour. The contributions of this study include (a) the application of the bend scour simulation model to the practical river flow simulation in the natural-irregular riverbed, (b) two proposed empirical equations for practical use in predicting shear stress and bend scour depth, and (c) the new proposed assessment methodology for rapidly predicting the risk of river embankment failure prior to field site investigation
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