---
title: "Define non-prismatic channel"
subject: "Hydraulics"
chapter: 5
key: "semester_4/hydraulics:define-non-prismatic-channel"
source: https://www.bctengineer.com/q/semester_4/hydraulics/define-non-prismatic-channel
site: BCT Engineering
---

# Define non-prismatic channel

Hydraulics · Chapter 5: Basics of Open channel flow

- Asked in: 2076 Baisakh, 1 marks; 2072 Asoj, 1 marks (asked 2 times)
- Video: [Types of Open Channel and Flow | Open Channel Flow | Hydraulics and Fluid Mechanics](https://www.youtube.com/watch?v=DxKJnR-Lnf4) — The Content Paradox
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_4/hydraulics/define-non-prismatic-channel
- Whole chapter: https://www.bctengineer.com/md/semester_4/hydraulics/chapter-5

## Question

Define non-prismatic channel.

## Short answer

A non-prismatic channel has changing cross-section shape, size, or slope along its length; area depends on both depth and distance. Examples: natural rivers, channel transitions.

## Answer

A **non-prismatic channel** is an open channel whose cross-sectional shape or size, or the bed slope, changes along its length. Its area depends on both depth and distance, $A=f(y,x)$.

Examples: all natural rivers and streams, a canal with transitions (contraction or expansion), a channel with a change of bed slope, or a channel with a change in width at a bridge.

```text
 Plan view of a transition
 ________
         \______   narrower section
 ________/ ______
```
Analysis (for example critical depth) of non-prismatic channels is done section by section, because properties such as $A$, $T$ and $R$ vary from one section to the next.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. A non-prismatic channel has
   A. Section or slope changing along the length
   B. Constant discharge only
   C. No flow
   D. Constant section
   Answer: A. Shape, size or slope varies. (Key point: Definition)

2. Its area is
   A. A = f(y)
   B. Zero
   C. A = constant
   D. A = f(y,x)
   Answer: D. It depends on distance also. (Key point: Area)

3. Which is non-prismatic?
   A. Long straight flume
   B. Constant circular culvert
   C. Natural river
   D. Uniform trapezoidal canal
   Answer: C. Natural rivers vary from section to section. (Key point: Example)

## Related in Hydraulics

- [Define prismatic channel](https://www.bctengineer.com/question.md?key=semester_4%2Fhydraulics%3Adefine-prismatic-channel) — Hydraulics, chapter 5, asked 2×
- [Define non-uniform open channel flow with examples](https://www.bctengineer.com/question.md?key=semester_4%2Fhydraulics%3Adefine-non-uniform-open-channel-flow) — Hydraulics, chapter 5
- [Design stable channel in 8 mm gravel](https://www.bctengineer.com/question.md?key=semester_4%2Fhydraulics%3Astable-channel-8mm-gravel-design) — Hydraulics, chapter 10

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