Uniform flow in open canals: which statements correctly describe the geometric and energy characteristics?

Introduction / Context:
In open-channel hydraulics, “uniform flow” is a fundamental idealization used for canal design and analysis. When flow is uniform, depth and velocity remain constant along the channel, making energy and geometry relationships especially clear and testable in practice.

Given Data / Assumptions:

• Steady, prismatic channel (constant cross-section and roughness).
• Uniform flow conditions: depth, velocity, and discharge remain constant with distance.
• No external work input (e.g., pumps) or withdrawals along the reach.

Concept / Approach:

Uniform flow implies a constant specific energy at each section apart from frictional dissipation balanced by the bed slope. The water surface slope, energy grade line slope, and bed slope are all equal and parallel. The hydraulic gradient coincides with the channel bed for uniform conditions, which is why the drop in water surface equals the head loss due to friction over a reach.

Step-by-Step Solution:

Verification / Alternative check:

Using Manning or Chezy for a reach with constant roughness and geometry, a constant normal depth y_n exists when S_f equals S_0, confirming the parallelism of bed and free surface and the energy balance.

Why Other Options Are Wrong:

Each of (a), (b), and (c) is individually true; selecting any single one omits the complete picture. Therefore “All the above” is the only fully correct choice.

Common Pitfalls:

Confusing gradually varied flow (non-uniform) with uniform flow; assuming parallel slopes in transitions or controls; ignoring that minor losses disturb exact equality over very short reaches.

Final Answer:

All the above.