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,
y_{c}  critical depth of the flow = \(\left [ \frac{q^2}{g} \right]^{\frac{1}{3}}\)
Here, q  discharge per unit width (m^{3}/s/m)
g  acceleration due to gravity (m/s^{2})
Calculation:
Given,
Critical depth, y_{c} = 2.0 m
Hence,
Critical specific energy,
E_{c} = \(\frac{3}{2}\) × y_{c} = \(\frac{3}{2}\) × 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,
y_{c}  critical depth (m)