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flow lines for these large angles. Because of the limited number of experiments, this
critical angle cannot be determined accurately.
The figure shows clearly the sensitivity of the sediment ratio for the angle of
diversion. It is interesting to mention that Bulle (
1926
) found a similar relation in
model experiments with critical angles between 90
and 120
.
For suspended load, the correlation between the diverting angle and the sediment
transport ratio is ultimately weak, which again shows that the nodal-point relation is
practically proportional for highly suspended sediment, independent of geometrical
conditions.
5 Conclusions
In this study, fluid flow and sediment transport in a channel bifurcation have been
simulated by means of the 3D flow modeling software FLUENT, which proves to
be a useful computation fluid dynamics tool for optimization purposes in the design
of hydraulic structures.
For suspended load, a practically entire conformity of sediment transport with
fluid motion is found, independent of geometrical conditions as the angle of the
diverting branch. The distribution of bed load is dependent on the shape of the
bifurcation. The amount of attracted sediment into the diverting branch is smallest
for the channel with a diverting angle of 45
, and highest for the channel with an
angle of 90
.
The results of sediment distribution are considered to be satisfying because both
nodal-point relations, (
2
) and (
3
) are fit to the cases of this study. Nevertheless, for
engineering purposes, the nodal-point relation (
3
) is preferred for the following
reasons:
l
For strongly nonlinear relations, (
3
) will behave better than a linear approxima-
tion like (
2
).
l
The relation (
3
) crosses the origin by definition (which is a physically logical
point in the relation).
l
Relation (
3
) shows the influence of the width ratio
B
1
/
B
2
.
l
Stability analysis in bifurcation equation (
2
) is useless because of its uncondi-
tional instability.
Acknowledgments The authors thank A.C.H. Kruisbrink for technical assistance and valuable
suggestions.
References
Bulle H (1926) Investigations on the trapping of bed-load in branching rivers. VDI-Verlag,
Forschungsarbeit auf dem Gebiet des Ing.wesens, Berlin, Heft 283
den Dekker P, van Voorthuizen JM (1994) Research on the morphological behaviour of bifurca-
tions in rivers. Delft University of Technology, Delft, the Netherlands
