Geoscience Reference
In-Depth Information
Changes of Sediment Distribution in a Channel
Bifurcation - 3D Modeling
Leszek Ksi˛˙ek and Douwe G. Meijer
1
Introduction
There are many factors involved in how suspended sediment and bed-load sediment
are distributed over the branches of a bifurcation. Some of these factors are:
l
Discharge
Q
0
and its distributions
Q
1
and
Q
2
over the branches.
l
Geometry of the bifurcation: cross sections
A
0
,
A
1,
and
A
2
(area and shape);
depths
h
0
,
h
1
, and
h
2
; widths
B
0
,
B
1
, and
B
2
; and angles
a
1
and
a
2
, slope angles
of the embankments.
l
Streamlining of bifurcation.
l
Conditions in the approaching channel: straight channel/bend flow, turbulence
intensity (caused by bed roughness/structures) sediment characteristics, particle
size and fall velocity, bed load/suspended transport.
l
Sediment management measures: sills, guide vanes, sediment extracting measures.
Physical model studies were performed by Bulle (
1926
), Riad (
1961
), Den
Dekker and Voorthuizen (
1994
), Islam (
2000
), and others. In general, it was
found that sediment distribution is generally more than linearly related to the
discharge distribution, a bigger diverting angle attracts more (bed load) sediment,
and highly suspended sediment (wash load) is distributed more or less proportion-
ally to the discharge distribution. Richardson and Thorne (
2001
), on the basis of
field measurements point out that the circumstances leading to the bifurcation of a
single channel are a topic of fundamental importance for understanding the physical
processes responsible for braiding. The main channel downstream the bifurcation
can carry less sediment load which may cause a degradation (Garde and Raju
2000
).
