Hydraulics and Open-Channel Flow Flashcards
7 cards from real Civil Engineering PE practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Hydraulics and Open-Channel Flow flashcards as text
A spillway has discharge coefficient Cd = 0.85, head H = 1.5 m, and length L = 10 m. The discharge over the spillway is most nearly:
Answer: 66 m³/s
Q = Cd(2/3)√(2g)·L·H^(3/2) = 0.85×(2/3)×4.429×10×1.837 ≈ 66 m³/s.
In gradually varied flow (GVF), an M2 profile occurs when:
Answer: Flow is subcritical and depth decreases toward critical depth downstream
M2 is a mild-slope profile where subcritical flow depth decreases downstream toward critical depth, occurring upstream of a free overfall.
The energy loss in a hydraulic jump in a rectangular channel is given by:
Answer: ΔE = (y₂ − y₁)³ / (4y₁y₂)
Energy loss in a hydraulic jump: ΔE = (y₂ − y₁)³ / (4y₁y₂), derived from energy and momentum equations.
A pipe transitions from 300 mm diameter to 600 mm diameter. If velocity in the smaller pipe is 3 m/s, the velocity in the larger pipe is:
Answer: 0.75 m/s
By continuity A₁V₁ = A₂V₂; V₂ = (D₁/D₂)²×V₁ = (0.3/0.6)²×3 = 0.25×3 = 0.75 m/s.
For a trapezoidal channel, the most hydraulically efficient section has which property?
Answer: Hydraulic radius equals half the water depth
The most efficient trapezoidal section (half-hexagon) has hydraulic radius R = y/2, minimizing wetted perimeter for a given area.
A suppressed rectangular weir (no end contractions) has L = 3 m, H = 0.5 m, and Cd = 0.61. Discharge is most nearly:
Answer: 1.91 m³/s
Q = (2/3)(0.61)(√19.62)(3)(0.5^1.5) = (2/3)(0.61)(4.429)(3)(0.354) ≈ 1.91 m³/s.
Specific energy in an open channel is measured relative to the:
Answer: Channel invert (bottom)
Specific energy E = y + V²/(2g) is measured relative to the channel bottom (invert), combining depth and velocity head.