Hydraulics and Open-Channel Flow Flashcards

The Chezy coefficient C is related to Manning's n by which expression (SI units)?

Answer: C = R^(1/6) / n

Equating Manning's V = (1/n)R^(2/3)S^(1/2) and Chezy's V = C√(RS) gives C = R^(1/6)/n.

Flow in a steep channel (S₀ > Sc) with depth greater than critical depth carries which GVF profile classification?

Answer: S1

An S1 profile occurs on steep slopes when y > yc; depth decreases downstream toward normal depth, with flow remaining supercritical.

A rectangular channel 3 m wide carries Q = 15 m³/s at normal depth with n = 0.014 and S₀ = 0.001. Normal depth is most nearly:

Answer: 1.75 m

Using Manning's iteratively: Q = (1/0.014)(3y)[(3y/(3+2y))^(2/3)](0.001^0.5) = 15 m³/s yields yn ≈ 1.75 m.

For a sluice gate in a wide rectangular channel with upstream depth y₁ = 2.0 m, gate opening a = 0.3 m, and Cc = 0.62, discharge per unit width assuming negligible velocity of approach is most nearly:

Answer: 1.17 m²/s

q = Cc·a·√(2g·y₁) = 0.62×0.3×√(2×9.81×2.0) = 0.186×6.264 ≈ 1.17 m²/s.

The primary purpose of a stilling basin downstream of a spillway is to:

Answer: Dissipate kinetic energy via a controlled hydraulic jump to prevent scour

A stilling basin forces a hydraulic jump, converting high-velocity supercritical flow to subcritical and dissipating kinetic energy to protect the downstream channel.

The standard step method for GVF computation differs from the direct step method primarily because the standard step:

Answer: Specifies distance increments and iterates to find the corresponding depth

The standard step method fixes the distance increment and iterates to find depth at each section; it applies to non-prismatic channels where cross-section geometry varies.

A circular conduit flowing at approximately 0.94D depth (not full) carries what fraction of its full-flow discharge?

Answer: About 108% of full-flow discharge

Due to circular pipe geometry, maximum discharge occurs near 0.94D depth and is approximately 108% of the full-pipe discharge.