Lacey's Regime Theory MCQ with answer and solution

Concept

Lacey's theory relates silt factor, velocity, hydraulic radius, and wetted perimeter for designing unlined channels in alluvium.

Formula

V = (1.08 × R² × S)^1/3, f = 1.76 × √d_mm

Step-by-step solution

1. Understand the purpose of Lacey's regime theory: It is formulated for designing stable alluvial channels. 2. Match the options with the application: Canal design involves determining cross-sectional dimensions (width, depth, slope) for stable flow. 3. Conclude that it is used for canal design.

Explanation

Lacey’s regime theory is a well-known empirical method developed by Gerald Lacey for the design of stable irrigation canals in alluvial soils where the silt is carried in suspension.

Why the other options are wrong

A: Pipe networks use Darcy-Weisbach or Hazen-Williams equations. B: Reservoir routing uses continuity equations and storage-discharge relationships. D: Groundwater movement follows Darcy's law.

Shortcut

Lacey's theory = Alluvial canal design.

Common mistake

Confusing it with pipe flow or surface hydrology routing techniques.