ASCE Water Resources and Environmental Engineering 2 — Questions and Answers
Question 1: Using the Rational Method, what is the peak runoff from a 10-acre site with C = 0.6 and rainfall intensity i = 2 in/hr?
- 120 cfs
- 1.2 cfs
- 3.3 cfs
- 12 cfs (Correct answer)
Correct answer: 12 cfs
Q = CiA = 0.6 × 2 × 10 = 12 cfs, since 1 acre-in/hr is approximately 1 cfs.
Question 2: A hydraulic jump forms in an open channel when flow changes from:
- Uniform to gradually varied
- Laminar to turbulent
- Supercritical to subcritical (Correct answer)
- Subcritical to supercritical
Correct answer: Supercritical to subcritical
A hydraulic jump is the abrupt shift from fast, shallow supercritical flow to slower, deeper subcritical flow.
Question 3: In open channel flow, a Froude number exactly equal to 1.0 indicates:
- Subcritical flow
- Laminar flow
- Supercritical flow
- Critical flow (Correct answer)
Correct answer: Critical flow
Fr = 1 means flow velocity equals the shallow-water wave celerity, which is critical flow.
Question 4: If the Hazen-Williams C coefficient of a pipe drops because of aging and tuberculation, what happens at the same flow rate?
- Head loss decreases
- Head loss is unchanged
- Head loss increases (Correct answer)
- Flow becomes laminar
Correct answer: Head loss increases
A lower C means a rougher pipe, so friction head loss goes up for the same discharge.
Question 5: In the NRCS (SCS) Curve Number method, a higher curve number means:
- Greater infiltration capacity
- Longer time of concentration
- Lower rainfall intensity
- Greater runoff potential (Correct answer)
Correct answer: Greater runoff potential
Higher CN values stand for less permeable surfaces and more direct runoff.
Question 6: Time of concentration for a watershed is best defined as the time:
- From the start of rainfall to the peak of rainfall intensity
- From the hydrograph peak to the end of baseflow
- For the full volume of runoff to leave the watershed
- For runoff to travel from the hydraulically most remote point to the outlet (Correct answer)
Correct answer: For runoff to travel from the hydraulically most remote point to the outlet
Tc is the travel time from the hydraulically most distant point, the point at which the whole watershed is contributing flow.
Question 7: An aquifer has hydraulic conductivity K = 10 m/day, hydraulic gradient 0.01, and cross-sectional area 100 m². What is the flow rate by Darcy's law?
- 100 m³/day
- 1 m³/day
- 10 m³/day (Correct answer)
- 0.1 m³/day
Correct answer: 10 m³/day
Q = KiA = 10 × 0.01 × 100 = 10 m³/day.
ASCE Water Resources and Environmental Engineering 2
Using the Rational Method, what is the peak runoff from a 10-acre site with C = 0.6 and rainfall intensity i = 2 in/hr?