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

# Define prismatic channel

Hydraulics · Chapter 5: Basics of Open channel flow

- Asked in: 2081 Chaitra, 1 marks; 2076 Baisakh, 1 marks (asked 2 times)
- Video: [Prismatic Channels](https://www.youtube.com/watch?v=USS5iSQhKrI) — Deen Fiaz
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_4/hydraulics/define-prismatic-channel
- Whole chapter: https://www.bctengineer.com/md/semester_4/hydraulics/chapter-5

## Question

Define prismatic channel.

## Short answer

A prismatic channel has constant cross-sectional shape, size, and bed slope along its length, so area depends only on depth. Example: long straight concrete canal.

## Answer

A **prismatic channel** is an open channel whose cross-sectional shape and size and bed slope do not change along its length. Its area is a function of depth only, $A=f(y)$.

Examples: a long straight rectangular or trapezoidal concrete canal, and a circular culvert of constant diameter and slope.

```text
 same section along the whole length
 ____________________________________
 |  []   |   []   |   []   |   []   |   (constant section, constant slope)
```
Most theoretical open channel formulas (uniform flow, GVF, critical depth computation) are derived for prismatic channels.

## Check yourself

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

1. A prismatic channel has
   A. Natural shape
   B. Constant cross-section and bed slope
   C. Varying discharge
   D. Varying section
   Answer: B. A depends only on y. (Key point: Definition)

2. For a prismatic channel, the area is
   A. A = f(y,x)
   B. Constant always
   C. A = f(y)
   D. Depends on time
   Answer: C. No dependence on distance. (Key point: Area)

3. Which is prismatic?
   A. A long straight rectangular concrete canal
   B. A bridge contraction
   C. A natural river
   D. A canal transition
   Answer: A. Constant section and slope. (Key point: Example)

## Related in Hydraulics

- [Define non-prismatic channel](https://www.bctengineer.com/question.md?key=semester_4%2Fhydraulics%3Adefine-non-prismatic-channel) — Hydraulics, chapter 5, asked 2×