Environmental Engineering Reference
In-Depth Information
100
80
60
40
WBP
BRO
ENG
RIJ
20
Figure 5.15. Accuracy of the
methods to predict the friction
factor for different error
factors
f
.
0
1.1
1.2
1.3
1.4
1.5
Error factor
the effect of the sidewalls is considered to be negligible. However, for
a non-wide canal the sidewalls will have a significant effect on the
friction factor. Especially the varying water depth above the sidewalls
and the roughness of the sidewalls without any bed form will require a
weighted friction factor;
•
the van Rijn method (1984c) to predict the friction factor appears to give
the best results when compared with the data from the Brownlie set.
Approximately 41%, 71%, 88%, 97% and 98% of
well-predicted
bed
forms for an error factor (
f
) of 1.1, 1.2, 1.3, 1.4 and 1.5 respectively are
obtained (Figure 5.15). The van Rijn method shows good results over
the whole range of measured friction factors.
5.3 GOVERNING EQUATIONS FOR SEDIMENT TRANSPORT
5.3.1
Introduction
Sediment transport predictors have often been applied on the basis of the
mean velocity as a variable without considering the variation in channel
geometry, distribution of the flow velocity and/or sediment transport in the
cross section (Simons and Senturk, 1992). Sediment transport predictors
have been developed for wide canals and they consider a channel with an
infinite width without taking into account the effect of the sidewalls on the
water flow and sediment transport. This ignorance of the effect of the side-
walls implies that the velocity and the sediment transport are considered
to be constant at any point of the cross section. Under these assumptions a
uniformly distributed shear stress on the bottom and an identical velocity
and sediment transport at any point over the canal width are assumed. In
this way, these variables can be easily expressed per unit width. For other,
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