Open-Channel Regime at Critical Depth – True or False? At the critical depth, the flow is termed critical (Froude number exactly 1). Torrential or supercritical flow corresponds to depths less than critical (Froude number greater than 1).

Introduction:
Terminology in open-channel hydraulics distinguishes critical, subcritical (tranquil), and supercritical (torrential) regimes by the Froude number Fr = V / sqrt(g * y_h). Mislabeling regimes leads to wrong control assumptions in channel design.

Given Data / Assumptions:

• Prismatic channel; hydraulic depth y_h applicable.
• Uniform gravitational field; negligible compressibility.
• Standard regime thresholds.

Concept / Approach:

Critical flow occurs at Fr = 1 and defines the critical depth for a given discharge and section. Supercritical (torrential) flow occurs when Fr > 1 (shallower, faster), while subcritical (tranquil) occurs when Fr < 1 (deeper, slower). Therefore the statement “flow at critical depth is torrential” is false.

Step-by-Step Solution:

Verification / Alternative check:

Specific-energy curves show minimum specific energy at critical depth; slopes of gradually varied profiles change character at this point, reinforcing that it is a distinct regime.

Why Other Options Are Wrong:

Yes: Contradicts the definition. Conditions on slope or Reynolds number do not redefine regime names. Depth and discharge jointly set Fr; regime names depend on Fr, not discharge alone.

Common Pitfalls:

Confusing “torrential” with any high-energy state; mixing Reynolds-number criteria (internal laminar/turbulent) with Froude-number criteria (open-channel regime).

Final Answer:

No