# In a rectangular channel section, if the critical depth is 2.0 m, the specific energy at critical depth is

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In a rectangular channel section, if the critical depth is 2.0 m, the specific energy at critical depth is

1.

3.0 m

2. 1.33 m
3. 2.5 m
4. 1.5 m

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Correct Answer - Option 1 :

3.0 m

Concept:

Critical Specific Energy:

• The specific energy corresponds to the critical depth of the flow is known as critical specific energy.
• For rectangular channel, it is equal to -

$E_c = \frac{3}{2}y_c$

Here,

yc - critical depth of the flow = $\left [ \frac{q^2}{g} \right]^{\frac{1}{3}}$

Here, q - discharge per unit width (m3/s/m)

g - acceleration due to gravity (m/s2)

Calculation:

Given,

Critical depth, yc = 2.0 m

Hence,

Critical specific energy,

Ec = $\frac{3}{2}$ × yc = $\frac{3}{2}$ × 2 = 3.0 m

• The following table shows the relationship between different types of sections and critical specific energy -
 Type of section Critical specific energy (m) 1. Rectangular $\frac{3}{2}y_c$ 2. Triangular $\frac{5}{4}y_c$ 3. Parabolic $\frac{4}{3}y_c$

Here,

yc - critical depth (m)