Water Resources and Environmental Engineering Flashcards

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?

Answer: 12 cfs

Q = CiA = 0.6 × 2 × 10 = 12 cfs, since 1 acre-in/hr is approximately 1 cfs.

A hydraulic jump forms in an open channel when flow changes from:

Answer: Supercritical to subcritical

A hydraulic jump is the abrupt shift from fast, shallow supercritical flow to slower, deeper subcritical flow.

In open channel flow, a Froude number exactly equal to 1.0 indicates:

Answer: Critical flow

Fr = 1 means flow velocity equals the shallow-water wave celerity, which is critical flow.

If the Hazen-Williams C coefficient of a pipe drops because of aging and tuberculation, what happens at the same flow rate?

Answer: Head loss increases

A lower C means a rougher pipe, so friction head loss goes up for the same discharge.

In the NRCS (SCS) Curve Number method, a higher curve number means:

Answer: Greater runoff potential

Higher CN values stand for less permeable surfaces and more direct runoff.

Time of concentration for a watershed is best defined as the time:

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.

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?

Answer: 10 m³/day

Q = KiA = 10 × 0.01 × 100 = 10 m³/day.