Open Channel Flow
JKSSB Junior Engineer (Civil) · Fluid Mechanics and Hydraulics · 22 practice questions with answers and explanations: 12 Easy, 8 Medium, 2 Hard.
Sample questions
Sample Easy question 1
In an open channel, the maximum velocity of flow occurs:
- At the free surface exactly
- A little below the free surface
- At the banks
- At the bed
Show answer
Answer: B. It is usually at 0.2 to 0.4 of the depth below the surface.
Sample Easy question 2
The normal depth in an open channel is the depth at which:
- The specific energy is minimum
- A hydraulic jump forms
- The flow is uniform
- The flow is critical
Show answer
Answer: C. At normal depth, the bed slope equals the energy slope.
Sample Easy question 3
In a very wide rectangular channel, the hydraulic radius is approximately equal to the:
- Twice the depth
- Width of the channel
- Depth of flow
- Half the width
Show answer
Answer: C. R = b y ÷ (b + 2y), which tends to y when b is much larger than y.
Sample Medium question 4
A channel carries water at 1.2 m depth and 2.5 m/s. The specific energy is about:
- 1.52 m
- 3.04 m
- 3.7 m
- 0.32 m
Show answer
Answer: A. E = y + v² ÷ 2g = 1.2 + 6.25 ÷ 19.62 = 1.519 m.
Sample Medium question 5
The Froude number before a hydraulic jump in a rectangular channel is 3. The ratio of the conjugate depths y₂ ÷ y₁ is about:
- 9
- 7.5
- 3.77
- 3
Show answer
Answer: C. y₂ ÷ y₁ = ½ (√(1 + 8 Fr²) − 1) = ½ (√73 − 1) = 3.77.
Sample Medium question 6
A hydraulic jump with an upstream Froude number between 1 and 1.7 is called:
- An oscillating jump
- A strong jump
- An undular jump
- A steady jump
Show answer
Answer: C. The surface is wavy and the energy loss is small.
Sample Hard question 7
With Manning's n = 0.02 and a hydraulic radius of 1.0 m, the Chezy coefficient C = R^(1/6) ÷ n is:
- 0.02
- 100
- 50
- 25
Show answer
Answer: C. C = 1^(1/6) ÷ 0.02 = 50.
Sample Hard question 8
A trapezoidal channel with a bed width of 3 m, side slopes 1 : 1 and a depth of 1.5 m has a hydraulic radius of about:
- 1.86 m
- 1.5 m
- 1.12 m
- 0.93 m
Show answer
Answer: D. A = (b + y) y = 6.75 m², P = b + 2y√2 = 7.24 m, so R = 0.93 m.