Lacey's Regime Theory MCQ with answer and solution

Concept

Laceys regime channel bed slope determination

Formula

S = f^5/3 / (3340 × Q^1/6)

Step-by-step solution

1. Kennedy’s theory does not give a direct formula for bed slope, necessitating trial and error using Kutter's equation. 2. Gerald Lacey developed a comprehensive regime theory for alluvial channels. 3. Lacey derived a direct regime slope equation: S = f^5/3 / (3340 × Q^1/6), eliminating trial and error. 4. Lacey also accounted for eddies originating from the entire wetted perimeter (bed and sides). Answer: A

Explanation

Lacey improved upon Kennedy’s canal design theory by eliminating trial-and-error procedures. Lacey provided a direct formula to compute the regime channel bed slope based on silt factor and design discharge: S = f^5/3 / (3340 × Q^1/6). Lacey also recognized that eddies are generated from the entire wetted perimeter, not just the bed.

Why the other options are wrong

B) Lacey emphasized the role of eddies across the entire wetted perimeter. C) Kennedy only considered bed eddies, whereas Lacey considered the entire perimeter. D) CVR (m) was introduced and used by Kennedy, not Lacey.

Shortcut

Lacey eliminated trial-and-error by providing a direct bed slope formula based on f and Q.

Common mistake

Thinking Lacey ignored side eddies or used Critical Velocity Ratio (CVR was Kennedy's parameter).