2D Numerical Modeling on the Transformation Mechanism of the Braided Channel

Shengfa Yang,Yi Xiao

doi:10.3390/w11102030

Abstract

This paper investigates the transformation mechanism between different channel patterns. A developed 2D depth-averaged numerical model is improved to take into account a bank vegetation stress term in the momentum conservation equation of flow. Then, the extended 2D model is applied to duplicate the evolution of channel pattern with variations in flow discharge, sediment supply and bank vegetation. Complex interaction among the flow discharge, sediment supply and bank vegetation leads to a transition from the braided pattern to the meandering one. Analysis of the simulation process indicates that (1) a decrease in the flow discharge and sediment supply can lead to the transition and (2) the riparian vegetation helps stabilize the cut bank and bar surface, but is not a key in the transition. The results are in agreement with the criterion proposed in the previous research, confirming the 2D numerical model’s potential in predicting the transition between different channel patterns and improving understanding of the fluvial process.

Highlights

Channel pattern refers to the limited reaches of the river that can be defined as straight, meandering or braided
As decreasing the discharge and sediment load respectively in run No.1 and 2, the main channel shifted to the right bank as the sand bars growing at the left bank; the shape of the cross section transit from “W” to “U”; the width ratio was lower and the depth of the channel in run No 3 was deeper than that of run No 1–2, it illustrated that the vegetation could increase tensile and shear strength, gave adequate time and conditions for development, such stabilization allows the existence of relatively steep cut banks, and might hinder the lateral migration of channels [41]
This paper presented research on the transformation mechanisms from a braided to meandering pattern by a numerical approach

Summary

Introduction

Channel pattern refers to the limited reaches of the river that can be defined as straight, meandering or braided. Straight rivers seldom occur in nature; meandering and braided rivers are common [1]. A sound understanding of the relationship between the control variables and channel pattern is fundamental to the development of improved management strategies in braided rivers [3]. The laboratory flume experiments have shed much light on the dynamic behavior of a wide braided river to a single-thread channel [4,5,6,7,8,9,10]. Various criteria have been proposed on the response of channel morphology to control variables [11,12,13,14]

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Discussion

Conclusion