Definition of uniform flow in open channels Uniform flow in an open channel is said to occur when which of the following is true along the reach considered?

Introduction / Context:
Uniform flow is a basic idealization in open-channel hydraulics used in Manning and Chezy formulations. Correctly identifying uniform conditions is crucial for reliable design of channels, canals, and sewers.

Given Data / Assumptions:

• Steady flow consideration.
• One-dimensional gradually varied assumptions.
• No lateral inflow/outflow for strict uniformity.

Concept / Approach:
Uniform flow means that hydraulic properties do not change spatially: depth y, area A, velocity V, and discharge Q are all constant along the reach. Consequently, the bed slope S, water surface slope, and energy grade line slope Sf are equal, and specific energy and total head per unit weight remain constant except for loss balanced by bed drop.

Step-by-Step Solution:

Verification / Alternative check:
Energy balance for uniform flow gives Sf = S0 (bed slope) and water surface slope equal to these; profiles are parallel.

Why Other Options Are Wrong:

• Lateral inflow/outflow makes discharge vary → non-uniform.
• Sf < S or Sf > S indicates accelerating or decelerating gradually varied flow.
• Uniform flow can occur in non-prismatic channels over short reaches if properties remain effectively constant; prismatic geometry is typical but not a strict logical requirement of the definition.

Common Pitfalls:
Confusing steady with uniform; equating “prismatic” with “uniform”; ignoring that uniform flow requires absence of spatial changes.

Final Answer:
Depth and mean velocity remain constant with distance along the channel.