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in comparison to other two models -Tank and Tokushima 7708506 Japan). Effects of Sand Bar
NAM.
325 ISLAM, G.M.T. (Institute of Water and
Flood Management, BUET, Dhaka).
UNSTEADY FLOW FIELDS OVER
FLOODPLAINS IN A MEANDERING
COMPOUND CHANNEL. IWFM Res. Bull.,
2003, 4, 33-49.
Natural rivers are predominantly meandering. The
cross-section of a natural river is usually composed
of a deep main channel and adjacent floodplains.
Even in case of a single section river, it is a
common practice to build embankments on both
sides of the channel for the purpose of flood
control, navigation and environmental
conservation. This results in a meandering
compound channel. This study explores the
structures of unsteady flow over the floodplains. It
is found that the unsteadiness parameter in the
rivers region varies from 15 to 20 whereas that in
the Jamuna river 80. The transverse distribution of
the primary velocity shows that the lateral profile
changes as the depth of water over the floodplain
changes. Horizontal eddies are seen to occur
around a region in between the bend apex of the
outer bank of the main channel and the side wall of
the outer levee. The primary velocity contours
have been discussed only for the peak flow in
unsteady flow condition and compared with that of
steady flow and it has found that there is no
appreciable difference between the two cases as far
as the flow structures are concerned. The stream-
wise distribution of longitudinal velocity suggests
that the flow structures between rising and falling
stage are different at different sections. The
exchange of flow between main channel and
floodplain drives secondary flow cells in the main
channel as well as in the floodplain. The evolution
and decay process of the secondary currents in the
floodplain has been explored.
326 ISLAM, G.M.T.; RAHMAN, M.M.;
HUSSAIN, M.A.; HAQUE, M.A.; HOQUE,
M.M. (Institute of Water and Flood Management,
BUET, Dhaka); HINOKIDANI, O. (Dept. of
Civil Engineering, Tottori University, Tottori 680- addition, a constant quantity of sediments of 1000
8552, Japan) & TAKEBAYSHI, H.(Dept. of
Civil Engineeing, The University of Tokushima,
99
on Sediment Distribution in an Alluvial River.
IWFM Res. Bull., 2004, 5, 36-40.
In this paper the distribution of sediments to the
branch channels formed by the sand bar has been
studied. The water discharge has been measured
and sediment discharge has been estimated in the
main channel as well as in the branch channels.
The sediment transport ratio of the downstream
branches of a sand bar has been compared with the
nodal point relation developed in the laboratory
condition.
327 ISLAM, M.Z. (Institute of Water and
Flood Management (IWFM),Bangladesh
University of Engineering and Technology
(BUET) Dhaka). GRAIN SIZE DISTRIBUTION
OF SEDIMENT MATERIALS DEPOSITED
OVER THE FLOODPLAIN DUE TO
EMBANKMENT FAILURE. IWFM Res. Bull.,
2001-2002, 3, 91-107.
Experimental runs 1-18 were conducted in a
distorted model of the Institute of Water and Flood
Management (IWFM), Bangladesh University of
Engineering and Technology(BUET) during 1998-
2000 to observe the grain size distribution of
sediment materials deposited over the floodplain
due to: (i) embankment breach; (ii) embankment
piping; (iii) embankment overtopping; (iv)
overland flow (without any embankment in-
between the river channel and the floodplain; and
(v) variable (higher & lower) discharges/velocities
into the floodplain through the embankment
breach. The model was made of reinforced cement
concrete including a floodplain and a river channel
with the length of 300 cm and widths of 90 cm and
22.5 cm respectively and an embankment made of
wooden plate installed in-between the floodplain
and the river channel. The breach, piping,
overtopping etc, were made in the embankment as
per requirement. The river channel and the
floodplain were constructed on the basis of vertical
and horizontal scale ratios of 100 and 1000
respectively. Each model run was carried out for
30 minutes. Before starting each model run, a
constant quantity of sediments of approximately 20
kg was mixed with water in the u/s basin. In
gm was added manually at the upper end of the