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

# Define non-uniform open channel flow with examples

Hydraulics · Chapter 5: Basics of Open channel flow

- Asked in: 2076 Bhadra, 2 marks
- Video: [Non-Uniform Flow](https://www.youtube.com/watch?v=kf5i4IIxzRs) — Kenneth Lamb
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_4/hydraulics/define-non-uniform-open-channel-flow
- Whole chapter: https://www.bctengineer.com/md/semester_4/hydraulics/chapter-5

## Question

Define non-uniform open channel flow with examples.

## Answer

**Non-uniform (varied) flow** is open channel flow in which the depth, and hence the velocity, changes from section to section along the channel: $\dfrac{\partial y}{\partial x}\neq0$. In steady non-uniform flow the discharge at a given section does not change with time, but the water surface is not parallel to the bed ($S_w\neq S_0$). It is divided into:

1. **Gradually varied flow (GVF)** where depth changes slowly. Example: backwater curve upstream of a weir or dam; flow in a canal with a change of bed slope.
2. **Rapidly varied flow (RVF)** where depth changes abruptly. Example: hydraulic jump, flow over a spillway crest or below a sluice gate.
3. **Spatially varied flow (SVF)** where discharge also changes along the length. Example: side weir, roadside gutter.

Natural rivers are non-uniform because their section and slope change from place to place. A uniform flow is only an idealised case of constant depth in a long prismatic channel.

## Check yourself

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

1. What defines non-uniform open channel flow?
   A. Depth and velocity change from section to section along the channel
   B. Discharge changes with time
   C. The channel has no slope
   D. Depth is constant but velocity changes
   Answer: A. In non-uniform flow dy/dx is not zero, so depth and velocity vary along the channel. (Key point: Definition)

2. In steady non-uniform flow, how is the water surface related to the bed?
   A. Parallel to the bed
   B. Not parallel to the bed (Sw is not equal to S0)
   C. Horizontal always
   D. Coincides with the EGL
   Answer: B. Depth changes, so the surface is not parallel to the bed. (Key point: Water surface)

3. Which is a correct classification of non-uniform flow?
   A. Laminar, turbulent, transitional
   B. Subcritical, critical, supercritical only
   C. Gradually varied, rapidly varied and spatially varied
   D. Steady, unsteady and uniform
   Answer: C. Non-uniform flow is divided into GVF, RVF and SVF. (Key point: Types)

4. Which is an example of rapidly varied flow?
   A. Backwater upstream of a weir
   B. Hydraulic jump
   C. Roadside gutter
   D. Long canal at normal depth
   Answer: B. A hydraulic jump has an abrupt depth change. Backwater is GVF and a gutter is SVF. (Key point: Examples)

## Related in Hydraulics

- [Conditions for uniform flow in open channel](https://www.bctengineer.com/question.md?key=semester_4%2Fhydraulics%3Aconditions-of-uniform-flow) — Hydraulics, chapter 6, asked 2×
- [Steady uniform, non-uniform and spatially varied flow](https://www.bctengineer.com/question.md?key=semester_4%2Fhydraulics%3Aflow-types-uniform-nonuniform-svf-examples) — Hydraulics, chapter 5, asked 4×
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- [Conditions for critical flow in open channel](https://www.bctengineer.com/question.md?key=semester_4%2Fhydraulics%3Acritical-flow-conditions-open-channel) — Hydraulics, chapter 7
- [Program for uniform depth in rectangular channel](https://www.bctengineer.com/question.md?key=semester_4%2Fhydraulics%3Aalgorithm-uniform-depth-rectangular) — Hydraulics, chapter 6
- [Define conveyance of an open channel](https://www.bctengineer.com/question.md?key=semester_4%2Fhydraulics%3Adefine-conveyance-open-channel) — Hydraulics, chapter 5, asked 2×

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