Uniform (prismatic) river section:\r A river reach is said to have a uniform section when its cross-section maintains a consistent geometrical shape along the reach. Which of the following standard shapes could represent such a uniform section?

Introduction / Context:
In open-channel hydraulics, a prismatic (uniform) section means the cross-sectional shape and size remain constant along the flow direction. Natural rivers approximate a range of shapes; artificial channels are often designed as rectangular or trapezoidal. Recognizing that multiple shapes can be uniform clarifies the concept.

Given Data / Assumptions:

• Uniform section = constant shape and dimensions along the reach.
• Possible shapes include circular segment, parabolic, rectangular, and trapezoidal geometries.

Concept / Approach:
Uniformity is independent of the specific shape; it relates to invariance along the reach. Any idealized shape can be considered uniform if repeated without change. Designers choose shapes for constructability, stability, and hydraulic efficiency (e.g., trapezoidal earth channels; rectangular lined channels).

Step-by-Step Reasoning:
Define uniform section: cross-section does not change with longitudinal distance.Evaluate options: each shape listed could be maintained consistently along a reach.Therefore, a, b, c, and d can all represent uniform sections.

Verification / Alternative check:
Textbook definitions of prismatic channels emphasize constant cross-section and slope; they do not restrict the geometry to one specific shape.

Why Other Options Are Wrong:

• Options a–d are all valid instances of uniform sections; the only fully correct response is the inclusive choice (e).

Common Pitfalls:

• Assuming only man-made shapes (rectangular/trapezoidal) can be uniform.
• Confusing uniform section with uniform flow (the latter refers to constant depth and velocity along the reach under equilibrium conditions).

Final Answer:
All of the above