Modeling Flow Pattern and Evolution of Meandering Channels with a Nonlinear Model

Leilei Gu,Shiyan Zhang,Yun Zhang,Li He,Willem Ottevanger,Koen Blanckaert,Dong Chen

doi:10.3390/w8100418

Abstract

Meander dynamics has been the focus of river engineering for decades; however, it remains a challenge for researchers to precisely replicate natural evolution processes of meandering channels with numerical models due to the high nonlinearity of the governing equations. The present study puts forward a nonlinear model to simulate the flow pattern and evolution of meandering channels. The proposed meander model adopts the nonlinear hydrodynamic submodel developed by Blanckaert and de Vriend, which accounts for the nonlinear interactions between secondary flow and main flow and therefore has no curvature restriction. With the computational flow field, the evolution process of the channel centerline is simulated using the Bank Erosion and Retreat Model (BERM) developed by Chen and Duan. Verification against two laboratory flume experiments indicates the proposed meander model yields satisfactory agreement with the measured data. For comparison, the same experimental cases are also simulated with the linear version of the hydrodynamic submodel. Calculated results show that the flow pattern and meander evolution process predicted by the nonlinear and the linear models are similar for mildly curved channels, whereas they exhibit different characteristics when channel sinuosity becomes relatively high. It is indicated that the nonlinear interactions between main flow and secondary flow prevent the growth of the secondary flow and induce a more uniform transverse velocity profile in high-sinuosity channels, which slows down the evolution process of meandering channels.

Highlights

The evolution of meandering channels is a complex geomorphological process driven by the interactions between fluid flow and alluvial channel beds and banks
A nonlinear meander evolution model was developed by coupling the hydrodynamic model of Blanckaert and de Vriend [5] and Bank Erosion and Retreat Model (BERM) of Chen and Duan [6]
The proposed model was tested with the flume experiments of da Silva [29] and Friedkin [30]

Summary

Introduction

The evolution of meandering channels is a complex geomorphological process driven by the interactions between fluid flow and alluvial channel beds and banks. Observations in recent flume experiments [1,2,3] have revealed that the flow pattern in a meander bend is closely related to its bed topography including the shallow point bars and deep pools developed near the inner and outer banks, respectively. Due to the difficulty in concurrently monitoring the flow pattern and channel migration in the field and laboratories, it remains unclear how fluid flow responds to the deformation of channel beds and in turn affects the evolution process of meandering channels. As the computational power rapidly grows in recent decades, numerical models emerge as economical and useful tools in meander studies, exhibiting its unique advantage in unraveling the complex interactions between fluid flow and alluvial beds. It remains a challenge to numerically replicate the natural evolution processes of the meandering channels especially for high-sinuosity channels due to possible strong nonlinear interactions in their evolution processes

Objectives

Findings

Discussion

Conclusion