chapter 3 hydraulics of open channel flow

3.8 Chapter Three
3.2.4 Compound Section Channels
In channels of compound section (Fig. 3.2), the specific energy correction factor α is not
equal to 1 and can be estimated by
A2
i
�
α � (3.20)
� K3
�
where K i and A i as follows the conveyance and area of the ith channel subsection, respectively,
K and A are conveyance are as follows:
and
N
K �� Ki i � 1
N
A �� Ai i � 1
N � number of subsections, and conveyance (K) is defined by Eq. (3.48) in Sec. 3.4.
Equation (3.20) is based on two assumptions: (1) the channel can be divided into subsections
by appropriately placed vertical lines (Fig. 3.2) that are lines of zero shear and do
not contribute to the wetted perimeter of the subsection, and (2) the contribution of the
nonuniformity of the velocity within each subsection is negligible in comparison with the
variation in the average velocity among the subsections.
3.3 MOMENTUM
HYDRAULICS OF OPEN CHANNEL FLOW
FIGURE 3.2 Channel with a compound section.
N
�
i � 1��K 3
i ��
3.3.1 Definition of Specific Momentum
The one-dimensional momentum equation in an open channel of arbitrary shape and a
control volume located between Sections 1 and 2 is
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A 2