Question

Lacey's theory is used for the design of

• A. Canal
• B. Regulator
• C. Fish ladder
• D. Apron

Hint:

Associate key theories with their applications in irrigation design:
- Kennedy's & Lacey's Regime Theories $\rightarrow$ Design of unlined canals in alluvial soil.
- Khosla's Theory $\rightarrow$ Design of foundations for weirs/barrages on permeable soil (to prevent piping failure).
- Bligh's Creep Theory $\rightarrow$ An older, simpler theory for the same purpose as Khosla's.

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
The question asks for the application of Lacey's regime theory.

Step 2: Detailed Explanation:
In irrigation engineering, the design of unlined canals that flow through alluvial (sandy/silty) soil is a major challenge. If the flow velocity is too high, the canal will scour its bed and banks. If the velocity is too low, silt will deposit and choke the canal.

Regime Theory, developed by engineers like Kennedy and later refined by

Lacey, addresses this problem. Lacey's theory provides a set of empirical equations that define the stable dimensions (width, depth, slope) of an alluvial

canal that is in "regime" - a state where there is neither silting nor scouring over time.
The theory allows engineers to design the cross-section and longitudinal slope of a canal based on the design discharge and a "silt factor," which characterizes the sediment being transported.
The other options are specific hydraulic structures, and their design is governed by different principles (structural engineering, hydraulics), not regime theory.

Step 3: Final Answer:
Lacey's theory is used for the design of stable, unlined alluvial canals.