Civil Engineering PE Exam Flashcards

In the Rational Method (Q = CiA) for estimating peak stormwater runoff, the variable 'i' represents:

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.

For a wide rectangular open channel (width much greater than depth), the hydraulic radius R is approximately equal to:

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.

A 100-year flood event has an annual exceedance probability of:

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.

Water hammer in a pressurized pipe system is primarily caused by:

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.

The SCS Curve Number (CN) method is used to estimate:

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.

Bernoulli's equation (z + P/γ + V²/2g = constant) applies strictly under which conditions?

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.

Specific energy E in an open channel is defined as energy per unit weight measured relative to:

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.