Flow distribution in diverging compound channels using improved independent subsection method

Bhabani Shankar Das,Kamalini Devi,Sebastien Proust,Kishanjit Kumar Khatua

doi:10.1051/e3sconf/20184005068

Bhabani Shankar Das, Kamalini Devi + Show 2 more

Open Access

https://doi.org/10.1051/e3sconf/20184005068

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Abstract

Experiments have been conducted in three diverging compound channels for different flow conditions to study the flow distribution in floodplain, upper and lower main channel. In a compound channel, vertical apparent shear exists on the interface between the upper main channel and the floodplain, which generally accelerates the flow on the floodplain and resists the flow in the upper main channel. In addition, a horizontal apparent shear stress also occurs on the interface between the upper and lower main channels, which generally accelerates the flow in the lower one and resists the flow in the upper one. Therefore, it is essential to consider the exchanges of momentum at both vertical and horizontal shear layer regions. In this paper, an attempt is made to improve the classical independent subsection method (ISM) to determine the magnitudes of flow and velocities in both upper and lower main channels. Four subsections are created in improved ISM according to the vertical and horizontal division lines that correspond to the vertical interface between the main channel and floodplain and the horizontal interface between upper and lower main channels respectively. The improved ISM consists in a set of four coupled 1D momentum equations (instead three equations of classical ISM) for subsections and a mass conservation equation for the total cross-section. The computed results show that the method is well capable of predicting the discharge distributions in the floodplain and main channel (both at upper and lower main channel).

Highlights

Flow modelling in the compound channel is challenging task for the river engineer
Proust [1], is the first to worked on diverging compound channels and presented an independent subsection method to model the flow depth and velocity at the different subsections of prismatic and non-prismatic compound channels
It is observed that the Ud/Q value at the main channel for higher angle 14.57 is slightly more than other diverging angles for all relative flow depth cases but less in floodplains due to the shorter diverging reach of 2m (Fig. 1c)

Summary

Introduction

Flow modelling in the compound channel is challenging task for the river engineer. When the geometry of floodplains diverges or converges, that affect significantly to the conveyance estimation. Flooding rivers usually present flow-width variations that give rise to non-uniform flows in non-prismatic compound geometries. Flow distribution in the diverging compound channel is a very important topic in river hydraulics to be investigated from a practical point of view in relation to flood risk assessment, bank protection, navigation and sediment-transport depositional pattern. Proust [1], is the first to worked on diverging compound channels and presented an independent subsection method to model the flow depth and velocity at the different subsections of prismatic and non-prismatic compound channels. Later Yonesi et al [3] worked on diverging compound channels with differential bed roughness for diverging angles 3.81°,5.7° and 11.3°. Due to non-prismatic effect of the floodplain the existing traditional methods like single channel method (SCM), divided channel method (DCM) and numerical methods like lateral distribution method (LDM), Shiono and Knight method (SKM) are failed to provide accurate stage, discharge, and velocity at different sections of the non-prismatic portion [4, 5, 6]

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Conclusion