Civil Engineering PE Hydraulics and Open-Channel Flow 4

Question 1

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:

Accepted Answer

2.4 m³/s

Answer

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.

Question 2

The momentum function (M) in open channel flow is most useful for analyzing:

Accepted Answer

Hydraulic jumps and rapidly varied flow

Answer

The momentum function M = Q²/(gA) + ȳA is conserved across a hydraulic jump, making it ideal for rapidly varied flow analysis.

Question 3

In the direct step method for GVF profile computation, the channel reach length Δx between two depth sections is computed as:

Accepted Answer

Δx = ΔE / (S₀ − S̄f)

Answer

The direct step method solves Δx = ΔE/(S₀ − S̄f), where ΔE is the specific energy change between two chosen depths.

Question 4

A 90° V-notch (triangular) weir with Cd = 0.60 measures a head H = 0.4 m. The discharge is most nearly:

Accepted Answer

0.071 m³/s

Answer

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.

Question 5

Normal depth in an open channel is the depth at which:

Accepted Answer

The gravitational driving force equals the friction resistance (uniform flow)

Answer

Normal depth occurs during uniform flow when the gravitational force exactly balances friction resistance, resulting in constant depth and velocity.

Civil Engineering PE Practice Test