ANSWER KEY CIVIL ENGINEERING Hydraulics and Hydrology Reviewer for Sanitary Engineer

Principles of Fluid Mechanics and Hydraulics

1. Which property of fluid is responsible for resistance to shear stress?
A. Density
B. Viscosity
C. Surface tension
D. Compressibility
Answer: B
Explanation: Viscosity is the measure of a fluid's resistance to shear stress or flow.

2. What is the unit of dynamic viscosity in the SI system?
A. Pascal-second (Pa·s)
B. Newton per meter (N/m)
C. Joule per second (J/s)
D. Kilogram per cubic meter (kg/m³)
Answer: A
Explanation: Dynamic viscosity is measured in Pascal-seconds (Pa·s), equivalent to N·s/m².

3. Which equation is based on the principle of conservation of energy in fluid flow?
A. Bernoulli’s Equation
B. Manning’s Equation
C. Darcy-Weisbach Equation
D. Reynolds Equation
Answer: A
Explanation: Bernoulli’s Equation expresses the conservation of energy for an ideal fluid in motion.

4. What happens to the pressure of a fluid as its velocity increases, according to Bernoulli’s principle?
A. Increases
B. Decreases
C. Remains the same
D. First decreases, then increases
Answer: B
Explanation: Bernoulli’s Principle states that as velocity increases, pressure decreases in a flowing fluid.

5. Which type of fluid flow is characterized by irregular and chaotic motion?
A. Laminar flow
B. Turbulent flow
C. Uniform flow
D. Steady flow
Answer: B
Explanation: Turbulent flow involves random, fluctuating fluid motion, while laminar flow is smooth.

6. The Reynolds number is used to determine the type of flow in a pipe. What is the critical Reynolds number for transition from laminar to turbulent flow?
A. 2,000
B. 4,000
C. 10,000
D. 1,000
Answer: A
Explanation: Laminar flow occurs when Re < 2,000, and turbulent flow occurs when Re > 4,000.

7. Which of the following instruments is commonly used to measure fluid pressure?
A. Venturi meter
B. Pitot tube
C. Manometer
D. Rotameter
Answer: C
Explanation: A manometer measures fluid pressure using liquid columns.

8. Which type of energy is dominant in a fluid at rest?
A. Kinetic energy
B. Pressure energy
C. Potential energy
D. Thermal energy
Answer: C
Explanation: Potential energy is due to the elevation of fluid in a gravitational field.

9. What is the primary cause of minor losses in a pipe system?
A. Pipe friction
B. Sudden expansion or contraction
C. Pipe length
D. Fluid viscosity
Answer: B
Explanation: Minor losses occur due to valves, bends, contractions, or expansions in a pipe system.

10. Which equation is used to calculate head loss due to friction in a pipe?
A. Bernoulli’s equation
B. Darcy-Weisbach equation
C. Manning’s equation
D. Hazen-Williams equation
Answer: B
Explanation: The Darcy-Weisbach equation is commonly used for head loss due to friction in pipes.

Open Channel Flow and Pipe Systems

11. Which equation is commonly used to determine flow velocity in open channels?
A. Manning’s equation
B. Darcy-Weisbach equation
C. Bernoulli’s equation
D. Reynolds equation
Answer: A
Explanation: Manning’s equation is used for open channel flow analysis.

12. A hydraulic jump occurs when flow changes from:
A. Laminar to turbulent
B. Turbulent to laminar
C. Supercritical to subcritical
D. Subcritical to supercritical
Answer: C
Explanation: A hydraulic jump occurs when supercritical flow slows to subcritical flow, dissipating energy.

13. What is the critical depth in an open channel?
A. The depth at which flow is subcritical
B. The depth at which flow is supercritical
C. The depth at which the specific energy is minimum
D. The maximum possible flow depth in a channel
Answer: C
Explanation: Critical depth occurs when the specific energy is at its minimum for a given discharge.

14. The velocity of flow in a circular pipe flowing full is determined using:
A. Manning’s equation
B. Darcy-Weisbach equation
C. Bernoulli’s equation
D. Froude’s equation
Answer: B
Explanation: The Darcy-Weisbach equation is used for calculating velocity and head loss in pipe flow.

15. Which of the following represents the most efficient cross-section for an open channel flow?
A. Rectangular channel
B. Circular channel
C. Triangular channel
D. Trapezoidal channel
Answer: D
Explanation: The trapezoidal channel is most efficient as it minimizes wetted perimeter, reducing friction losses.

16. In pipe network analysis, which method is commonly used to balance flows and pressures?
A. Bernoulli’s Method
B. Manning’s Method
C. Hardy Cross Method
D. Rational Method
Answer: C
Explanation: The Hardy Cross Method is an iterative approach for solving pipe network flow distributions.

17. Which factor affects the friction loss in a pipe?
A. Pipe length
B. Pipe roughness
C. Flow velocity
D. All of the above
Answer: D
Explanation: Friction loss in pipes depends on length, roughness, velocity, and fluid properties.

18. What is the primary cause of water hammer in pipelines?
A. Pipe corrosion
B. Rapid valve closure
C. Pipe expansion
D. Water temperature changes
Answer: B
Explanation: Water hammer occurs due to sudden changes in velocity, such as rapid valve closures.

19. Which of the following statements about minor losses in pipe flow is true?
A. They are only significant in very long pipelines
B. They are caused by changes in flow direction or obstruction
C. They are independent of velocity
D. They are neglected in most practical designs
Answer: B
Explanation: Minor losses occur due to bends, fittings, expansions, and contractions in the pipeline.

20. For an open channel, what does the Froude number (Fr) determine?
A. Whether flow is laminar or turbulent
B. Whether flow is subcritical, critical, or supercritical
C. The energy loss due to friction
D. The volume of flow per unit time
Answer: B
Explanation: The Froude number (Fr) classifies flow as subcritical (Fr < 1), critical (Fr = 1), or supercritical (Fr > 1).

Hydrology

21. Which process in the hydrological cycle describes water movement from plants to the atmosphere?
A. Evaporation
B. Transpiration
C. Infiltration
D. Runoff
Answer: B
Explanation: Transpiration is the release of water from plants to the atmosphere.

22. Which of the following best defines the runoff coefficient?
A. The fraction of rainfall that becomes surface runoff
B. The ratio of infiltration to rainfall
C. The percentage of rainfall lost to evaporation
D. The amount of rainfall that percolates into groundwater
Answer: A
Explanation: The runoff coefficient represents how much rainfall turns into runoff.

23. Which instrument is used to measure rainfall intensity?
A. Evaporimeter
B. Barometer
C. Hygrometer
D. Rain gauge
Answer: D
Explanation: A rain gauge measures rainfall depth and intensity over time.

24. What is the primary driving force of the hydrologic cycle?
A. Gravity
B. Solar radiation
C. Wind movement
D. Atmospheric pressure
Answer: B
Explanation: Solar radiation drives evaporation, transpiration, and the entire hydrological cycle.

25. Which factor does NOT significantly affect infiltration capacity?
A. Soil type
B. Vegetation cover
C. Wind speed
D. Rainfall intensity
Answer: C
Explanation: Wind speed has little impact on infiltration, while soil, vegetation, and rainfall intensity are crucial.

26. A hydrograph is a plot of:
A. Rainfall intensity versus time
B. River discharge versus time
C. Evaporation rate versus time
D. Groundwater level versus time
Answer: B
Explanation: A hydrograph shows discharge variations over time, useful for flood analysis.

27. Which of the following is an example of a non-point source of water pollution?
A. Industrial discharge from a factory
B. Oil spill from a ship
C. Urban runoff
D. Sewage treatment plant discharge
Answer: C
Explanation: Non-point sources are diffuse, such as urban runoff, agricultural drainage, and sedimentation.

28. What is the Rational Method primarily used for?
A. Estimating peak runoff from a watershed
B. Calculating infiltration rates
C. Measuring evaporation losses
D. Determining groundwater recharge
Answer: A
Explanation: The Rational Method estimates peak discharge (Q = C × I × A) for small urban watersheds.

29. Flood forecasting relies on which of the following data sources?
A. Rainfall intensity measurements
B. River stage readings
C. Watershed characteristics
D. All of the above
Answer: D
Explanation: Flood forecasting combines rainfall data, river levels, watershed conditions, and past records.

30. Which process describes the movement of water through soil into groundwater reservoirs?
A. Infiltration
B. Percolation
C. Evaporation
D. Transpiration
Answer: B
Explanation: Percolation is the downward movement of water through soil layers to recharge groundwater.

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