Water and Hydraulics Structures Branch / 3rd Class [Hydraulic Structures]

Lect.No.4-First Semester [Critical Flow Computations]

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Water and Hydraulics Structures Branch / 3rd Class [Hydraulic Structures]

Lect.No.4-First Semester [Critical Flow Computations]

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Water and Hydraulics Structures Branch / 3rd Class [Hydraulic Structures]

Lect.No.4-First Semester [Critical Flow Computations]

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**** For a rectangular channel section of bottom width b, the Froude number is

expressed as;

where, q=Q/b=discharge per unit width and is defined for rectangular channels

only. Then the expression for the critical depth becomes;

…………………… (6)

**** For a triangular channel with side slopes of “m” (that is 1 vertical over m

horizontal), the critical depth calculated as;

…………………… (7)

**** For a trapezoidal channel with side slopes of m (that is 1 vertical over m

horizontal), Fr = Fr2 = 1, will lead to;

……………… (8)

Eq.8 cannot be solved for (yc) explicitly. Therefore, a trial-and-error procedure is

needed to determine the critical depth for trapezoidal channels. Alternatively, can

Figure (T), can be used, which presents a graphical solution for Eq.8 in

dimensionless form.

Water and Hydraulics Structures Branch / 3rd Class [Hydraulic Structures]

Lect.No.4-First Semester [Critical Flow Computations]

Asst. Prof. Dr. Jaafar S. Maatooq 4 of 11

Figure (T)

**** Likewise, for a circular channel of diameter d0, we can show that

(Henderson,1966)

……………… (9)

Where;

An explicit solution to Eq.9 for yc is not available; so it solved by trial and error.

However, a graphical solution is provided in Figure (C) to facilitate the calculation

of the critical depth in circular channels.

Water and Hydraulics Structures Branch / 3rd Class [Hydraulic Structures]

Lect.No.4-First Semester [Critical Flow Computations]

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Figure (C)

Water and Hydraulics Structures Branch / 3rd Class [Hydraulic Structures]

Lect.No.4-First Semester [Critical Flow Computations]

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Lect.No.4-First Semester [Critical Flow Computations]

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Lect.No.4-First Semester [Critical Flow Computations]

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Lect.No.4-First Semester [Critical Flow Computations]

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Lect.No.4-First Semester [Critical Flow Computations]

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Lect.No.4-First Semester [Critical Flow Computations]

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