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.
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A circular culvert D = 900 mm flows full with L = 30 m, n = 0.013, and S = 0.005. Normal discharge using Manning's equation is most nearly:
Answer: 2.4 m³/s
A = π(0.9)²/4 = 0.636 m², R = 0.225 m; Q = (1/0.013)(0.636)(0.225^0.667)(0.005^0.5) ≈ 2.4 m³/s.
The momentum function (M) in open channel flow is most useful for analyzing:
Answer: Hydraulic jumps and rapidly varied flow
The momentum function M = Q²/(gA) + ȳA is conserved across a hydraulic jump, making it ideal for rapidly varied flow analysis.
In the direct step method for GVF profile computation, the channel reach length Δx between two depth sections is computed as:
Answer: Δx = ΔE / (S₀ − S̄f)
The direct step method solves Δx = ΔE/(S₀ − S̄f), where ΔE is the specific energy change between two chosen depths.
A 90° V-notch (triangular) weir with Cd = 0.60 measures a head H = 0.4 m. The discharge is most nearly:
Answer: 0.071 m³/s
Q = (8/15)Cd√(2g)·tan(45°)·H^(5/2) = (8/15)(0.60)(4.429)(1)(0.4^2.5) = 1.416×0.1012 ≈ 0.071 m³/s.
Normal depth in an open channel is the depth at which:
Answer: The gravitational driving force equals the friction resistance (uniform flow)
Normal depth occurs during uniform flow when the gravitational force exactly balances friction resistance, resulting in constant depth and velocity.
A broad-crested weir has crest elevation 100 m, upstream water surface at 101.8 m, width L = 5 m, and Cd = 0.848. Discharge is most nearly:
Answer: 14.6 m³/s
H = 1.8 m; Q = 1.705·Cd·L·H^(3/2) = 1.705×0.848×5×(1.8)^1.5 ≈ 14.6 m³/s.
When a subcritical flow channel width narrows sufficiently, 'choking' occurs at the constriction. This means:
Answer: Critical depth is forced at the throat, limiting the discharge
Choking forces critical depth at the throat when the available specific energy equals the minimum required; the upstream depth must rise to supply additional energy.