Lacey’s regime condition: According to Lacey, regime flow is obtained under which foundational circumstance for an alluvial channel?

Introduction / Context:
Lacey’s regime theory provides relationships for stable alluvial channels. A core premise is the nature of the bed and bank material relative to the sediments being transported.

Given Data / Assumptions:

• Alluvial channel, sediment-laden flow.
• Interest in the foundational boundary condition that enables regime development.

Concept / Approach:
Lacey postulated that a channel attains regime when it is flowing through unlimited (unconfined) incoherent alluvium whose properties match those of the transported sediment. Under steady conditions, the channel gradually reshapes to achieve balance between sediment supply and carrying capacity.

Step-by-Step Solution:
Confirm alluvium is incoherent (loose), not cemented or rock.Assure the alluvium’s character is similar to the moving sediment.Allow the channel to evolve under steady conditions until equilibrium geometry emerges.

Verification / Alternative check:
When bed/bank material differs strongly from transported sediment (e.g., cohesive banks), regime equations become less reliable and bank processes dominate rather than mutual adjustment.

Why Other Options Are Wrong:
Variable silt grade/charge and discharge undermine steady regime; persistent variability prevents a stable geometry.

Common Pitfalls:

• Assuming regime depends only on discharge; sediment and boundary conditions are equally vital.
• Applying regime equations to rigid channels.

Final Answer:
The channel flows in unlimited, incoherent alluvium of the same character as the transported material