Velocity Distribution in Open Channels — Is It Uniform? State whether the following is true or false: “The velocity of flow is the same at all points across the cross-section of an open channel.”

Introduction:Understanding velocity distribution across a cross-section is crucial for accurate discharge measurement and sediment transport analysis. Real flows exhibit shear near boundaries, creating non-uniform profiles.

Given Data / Assumptions:

• Steady, fully developed open-channel flow.
• No slip at the boundaries (bed and banks) and free surface exposed to atmosphere.
• Prismatic channel for conceptual clarity.

Concept / Approach:Viscous and turbulent shear cause velocity to vary from near zero at the bed and banks to a maximum just below the free surface. Hence, only an average (mean) velocity is uniform in the sense of a single representative value; point velocities differ across the section.

Step-by-Step Solution:Recall boundary condition: velocity approaches zero at solid boundaries.Recognize free-surface shear is small; thus peak velocity occurs slightly below the surface.Therefore the statement of uniform velocity across the section is false.

Verification / Alternative check:Velocity-area method uses a velocity distribution (via current meters or ADCP) precisely because velocities vary spatially; this confirms non-uniformity.

Why Other Options Are Wrong:Choosing “True” would neglect shear and turbulence—contrary to basic fluid mechanics.

Common Pitfalls:Assuming plug flow because textbooks draw simplified diagrams; confusing time-steady flow with spatially uniform profiles.

Final Answer:False