Dams, Spillways and River Training
JKSSB Junior Engineer (Civil) · Irrigation Engineering · 19 practice questions with answers and explanations: 13 Easy, 4 Medium, 2 Hard.
Sample questions
Sample Easy question 1
Compared with an earth dam, a masonry or concrete gravity dam needs:
- A weaker foundation
- A clay core
- A strong foundation, usually rock
- No foundation
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Answer: C. The high concentrated loads of a gravity dam need a sound rock foundation.
Sample Easy question 2
Uplift pressure under a gravity dam:
- Reduces the effective weight of the dam
- Increases the stability
- Has no effect on stability
- Acts only on earth dams
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Answer: A. Drainage galleries are provided to reduce it.
Sample Easy question 3
The phreatic line in an earth dam is the:
- Line of the spillway crest
- Top line of seepage within the embankment
- Line of maximum pressure
- Bottom of the foundation
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Answer: B. The downstream slope should stay above the point where it emerges.
Sample Medium question 4
A gravity dam has a total vertical force of 6,000 kN, a horizontal thrust of 3,000 kN and a coefficient of friction of 0.7. The factor of safety against sliding is:
- 1.4
- 0.71
- 2
- 0.35
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Answer: A. FS = μ ΣV ÷ ΣH = 0.7 × 6,000 ÷ 3,000 = 1.4.
Sample Medium question 5
The resisting moment of a dam about its toe is 12,000 kN·m and the overturning moment is 6,000 kN·m. The factor of safety against overturning is:
- 6,000
- 0.5
- 3
- 2
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Answer: D. FS = resisting moment ÷ overturning moment.
Sample Medium question 6
A pan evaporimeter shows an evaporation of 8 mm in a day, and the pan coefficient is 0.7. The lake evaporation is:
- 2.8 mm
- 5.6 mm
- 11.4 mm
- 8 mm
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Answer: B. Lake evaporation = pan coefficient × pan evaporation.
Sample Hard question 7
By the rational formula Q = C I A ÷ 360, with C = 0.4, I = 60 mm/h and A = 50 hectares, the peak runoff is:
- 1,200 m³/s
- 3.33 m³/s
- 0.33 m³/s
- 6.67 m³/s
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Answer: B. Q = 0.4 × 60 × 50 ÷ 360 = 3.33 m³/s.
Sample Hard question 8
The discharge over an ogee spillway is Q = C L H^(3/2). With C = 2.2, L = 20 m and H = 1.5 m, Q is about:
- 161.7 m³/s
- 121.2 m³/s
- 66 m³/s
- 80.8 m³/s
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Answer: D. Q = 2.2 × 20 × 1.5^1.5 = 80.8 m³/s.