Flow and Velocity Distribution in Meandering Compound
Channels
Kanhu Charan Patra
1
; Srijib K. Kar
2
; and Amartya K. Bhattacharya, A.M.ASCE
3
Abstract: An investigation of flow and velocity distribution in meandering compound channels with over bank flow is described.
Equations concerning the three-dimensional variation of longitudinal, transverse, and vertical velocity in the main channel and floodplain
of compound section in terms of channel parameters are presented. The flow and velocity distributions in meandering compound channels
are strongly governed by interaction between flow in the main channel and that in the floodplain. The proposed equations take adequate
care of the interaction affect. Results from the formulations, simulating the three-dimensional velocity field in the main channel and in the
floodplain of meandering compound channels are compared with their respective experimental channel data obtained from a series of
symmetrical and unsymmetrical test channels with smooth and rough sections. The aspect ratio of the test channels varies from two to
five. The equations are found to be in good agreement with the experimental data. The formulations are verified against the natural river
and other meandering compound channel data. The power laws used for simulating the three-dimensional velocity structure are found to
be quite adequate.
DOI: 10.1061/ASCE0733-94292004130:5398
CE Database subject headings: Meanders; Flood plains; Velocity distribution; Flow distribution; Channels, waterways.
Introduction
A river is the author of its own geometry. It is an established fact
that meandering represents a degree of adjustment of water and
sediment laden river with its size, shape, and slope such that a
flatter channel can exist in a steeper valley. By nature or by de-
sign, rivers have compound sections consisting of a main channel,
which always carry low flows and one or more side floodplains,
which carry flow above the bank full stages. Once a river stage
overtops the banks, the cross sectional geometry of flow under-
goes a steep change, a situation common to most of the natural or
man-made channels. The flow structure in a compound channel is
characterized by large shear layers generated by the difference of
velocity between the main channel and the floodplain flow. There
is also a wide variation in the distribution of longitudinal velocity
from the inner to the outer bank of a meandering compound chan-
nel section. Due to the continuous streamwise variation of radius
of curvature, the flow parameters are considerably more complex
in a meandering channel than in a straight channel. The flow
geometry in a meandering channel is in the state of either devel-
opment or decay or both.
Distribution of flow and velocity in a meandering river are
important topics in river hydraulics to be investigated from a
practical point of view in relation to the bank protection, naviga-
tion, water intakes, and sediment transport-depositional patterns.
Knowledge on velocity distribution in a channel also helps to
determine the energy expenditure, bed shear stress distribution,
and the associated heat and mass transport problems. An attempt
is made here for an analytical solution of a three-dimensional
flow structure in meandering compound channel to get a complete
picture of velocity distribution at any section of a meandering
path. More efforts have been made to model the distribution of
flow between the main channel and floodplain of a meandering
compound channel.
The usual practice in one-dimensional 1D analysis of com-
pound channel is to calculate separately the flow that can be con-
veyed by the various discrete subareas of a compound section as
if the subareas are independent. For each subarea, either a Man-
ning or Darcy-Weisbach equation is used to calculate the convey-
ance capacity using appropriate values for the area, wetted perim-
eter, and roughness coefficients of the subareas. The individual
discharges are then added to give the total discharge carried by
the compound section. The roughness coefficient n or f is a some-
what crude measure of the net effect of the influences of the shear
and the secondary flow, wherein all the hydraulic effects are
lumped into a simple bulk resistance parameter. Using ‘‘divided
channel’’ method of Lotter 1933 and following the work of
Wormleaton, Allen, and Hadjipanos 1982, Knight and Dem-
etriou 1983, and Knight and Hamed 1984 for straight chan-
nels, Patra and Kar 2000 proposed a variable interface plane of
separation of compound channel for a better estimate of discharge
in meandering and straight compound river sections. The percent-
ages of total flow carried by the main channel and floodplain of a
compound section in terms of four dimensionless channel param-
eters were suitably modeled. The effect of flow interaction be-
tween the floodplain and main channel for various depths of flow
over floodplain was adequately taken care of.
1
Associate Professor, Civil Engineering Dept., College of Engineering
and Technology, Orissa Univ. of Agricultural and Technology,
Bhubaneswar, Orissa, India—751 003.
2
Professor, Civil Engineering Dept., Indian Institute of Technology,
Kharagpur, India—721302. E-mail: skkar@civiliitkgp.ernet.in
3
Lecturer, Applied Mechanics Dept., B.E. Coll. Deemed Univ.,
Howrah, W.B. India.
Note. Discussion open until October 1, 2004. Separate discussions
must be submitted for individual papers. To extend the closing date by
one month, a written request must be filed with the ASCE Managing
Editor. The manuscript for this paper was submitted for review and pos-
sible publication on May 23, 2000; approved on February 25, 2003 . This
paper is part of the Journal of Hydraulic Engineering, Vol. 130, No. 5,
May 1, 2004. ©ASCE, ISSN 0733-9429/2004/5-398 – 411/$18.00.
398 / JOURNAL OF HYDRAULIC ENGINEERING © ASCE / MAY 2004