NCEES Civil Engineering PE Exam 2 — Questions and Answers
Question 1: In the Rational Method (Q = CiA) for estimating peak stormwater runoff, the variable 'i' represents:
- Infiltration rate in inches per hour
- Rainfall intensity in inches per hour for a storm duration equal to the time of concentration (Correct answer)
- Initial abstraction in inches
- Imperviousness factor of the watershed
Correct answer: Rainfall intensity in inches per hour for a storm duration equal to the time of concentration
In the Rational Method, 'i' is the rainfall intensity (in./hr) obtained from an IDF curve for a storm duration equal to the watershed's time of concentration.
Question 2: For a wide rectangular open channel (width much greater than depth), the hydraulic radius R is approximately equal to:
- The flow depth y (Correct answer)
- Half the flow depth, y/2
- The channel width B
- The product of width and depth, B×y
Correct answer: The flow depth y
For a wide rectangular channel: R = A/P = (B×y)/(B + 2y) ≈ B×y/B = y when B >> y, so R ≈ y.
Question 3: A 100-year flood event has an annual exceedance probability of:
- 100%
- 10%
- 1% (Correct answer)
- 0.1%
Correct answer: 1%
Annual exceedance probability P = 1/T = 1/100 = 0.01 = 1%, meaning any given year has a 1% chance of experiencing a flood of this magnitude or greater.
Question 4: Water hammer in a pressurized pipe system is primarily caused by:
- Long-term pipe corrosion gradually reducing the pipe cross-section
- Rapid changes in flow velocity such as sudden valve closure (Correct answer)
- Sustained high static pressure exceeding the pipe design rating
- Dissolved air slowly coming out of solution over time
Correct answer: Rapid changes in flow velocity such as sudden valve closure
Water hammer is a pressure transient caused by rapid deceleration of flow (e.g., sudden valve closure), converting kinetic energy to pressure energy and generating pressure waves that propagate through the system.
Question 5: The SCS Curve Number (CN) method is used to estimate:
- Peak runoff discharge directly in cubic feet per second
- Direct runoff depth in inches from a given rainfall depth (Correct answer)
- Time of concentration for a watershed
- Channel routing of a flood hydrograph
Correct answer: Direct runoff depth in inches from a given rainfall depth
The CN method calculates direct runoff depth Q (in inches) from rainfall depth P (in inches) using Q = (P − 0.2S)² / (P + 0.8S), where S = (1000/CN) − 10.
Question 6: Bernoulli's equation (z + P/γ + V²/2g = constant) applies strictly under which conditions?
- Compressible, viscous, and unsteady flow
- Incompressible, inviscid, steady flow along a streamline (Correct answer)
- Turbulent flow accounting for friction head losses
- Variable-density flow with heat exchange
Correct answer: Incompressible, inviscid, steady flow along a streamline
Bernoulli's equation is derived from Euler's equation under assumptions of steady, inviscid (frictionless), incompressible flow along a streamline, with no energy addition or removal.
Question 7: Specific energy E in an open channel is defined as energy per unit weight measured relative to:
- The channel bottom (bed) as the local datum (Correct answer)
- Mean sea level as a fixed external datum
- The local water surface elevation
- The centerline elevation of the flow cross-section
Correct answer: The channel bottom (bed) as the local datum
Specific energy E = y + V²/2g uses the channel bottom as its datum, combining flow depth and velocity head without including the external elevation head z.
NCEES Civil Engineering PE Exam 2
In the Rational Method (Q = CiA) for estimating peak stormwater runoff, the variable 'i' represents: