---
title: "Canal distribution system with sketch"
subject: "Irrigation and Drainage Engineering"
chapter: 3
key: "semester_6/irrigation_and_drainage_engineering:canal-distribution-system-sketch"
source: https://www.bctengineer.com/q/semester_6/irrigation_and_drainage_engineering/canal-distribution-system-sketch
site: BCT Engineering
---

# Canal distribution system with sketch

Irrigation and Drainage Engineering · Chapter 3: Canal Irrigation System

- Asked in: 2079 Asoj, 3 marks; 2074 Bhadra, 2 marks (asked 2 times)
- Video: [Canal distribution system](https://www.youtube.com/watch?v=1lw3qfSo7NM) — MUKUND MURARI DAS
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/irrigation_and_drainage_engineering/canal-distribution-system-sketch
- Whole chapter: https://www.bctengineer.com/md/semester_6/irrigation_and_drainage_engineering/chapter-3

## Question

Describe with sketch the canal distribution system (suitable in the Terai region of Nepal).

## Short answer

In the Terai, a gravity canal network diverts river water via a barrage into a main canal aligned along ridges. Branch canals, distributaries, and minors carry water to outlets, which supply field channels. Cross-drainage works and drains prevent flooding and waterlogging.

## Answer

In the Terai, the rivers bring water from the hills and the land has a gentle slope, so a **gravity canal network** is used. Water is diverted by a barrage or weir and carried in stages.

```text
 River --[Barrage/Headworks]
             |
        MAIN CANAL
        /          \
   BRANCH CANAL    BRANCH CANAL
      |    \
 DISTRIBUTARY  DISTRIBUTARY
      |
    MINOR
      |
    OUTLET
      |
 WATERCOURSE / FIELD CHANNELS --> FIELDS
```

- **Main canal:** takes off at the head regulator; aligned along the ridge (watershed) as far as possible.
- **Branch canals:** take off from the main canal through branch head regulators (with a cross-regulator in the main canal just downstream to head up the water); they irrigate large blocks.
- **Distributaries and minors:** carry about 0.25-3 cumec (minors less than about 0.25 cumec) and run along the minor ridges of the area.
- **Outlets:** control the discharge into the watercourses; modules or pipe outlets are used.
- **Field channels:** farmers' channels, supplied in turn by rotation (warabandi).
- Drains and cross-drainage works (aqueducts, culverts) keep the system safe from floods and waterlogging.

Canals run along ridge lines (watershed alignment) so that the command is as large as possible.

## Check yourself

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

1. Why is a gravity canal network used in the Terai?
   A. Gentle land slope and river water diverted by barrage allow gravity flow
   B. The land is steep
   C. Pumping is cheaper
   D. Rainfall is absent
   Answer: A. Gentle slope plus a diversion barrage supports gravity flow. (Key point: Terai system type)

2. How is the main canal aligned?
   A. Along the lowest valley
   B. Along the ridge (watershed) as far as possible
   C. Along a contour only
   D. Perpendicular to the river
   Answer: B. Ridge alignment gives maximum command. (Key point: Main canal alignment)

3. What is the order of water flow?
   A. Branch, main, outlet, minor
   B. Outlet, minor, branch, main
   C. Main canal, branch, distributary/minor, outlet, watercourse, field
   D. Distributary, main, field, branch
   Answer: C. Water is carried in stages from large to small channels. (Key point: Flow sequence)

## Related in Irrigation and Drainage Engineering

- [Water logging remedies and surface drainage in Terai](https://www.bctengineer.com/question.md?key=semester_6%2Firrigation_and_drainage_engineering%3Awater-logging-causes-surface-drainage-terai) — Irrigation and Drainage Engineering, chapter 9
- [Internal/external drainage; water logging; Terai surface drainage](https://www.bctengineer.com/question.md?key=semester_6%2Firrigation_and_drainage_engineering%3Ainternal-external-drainage-water-logging-terai) — Irrigation and Drainage Engineering, chapter 9
- [Components of canal irrigation system](https://www.bctengineer.com/question.md?key=semester_6%2Firrigation_and_drainage_engineering%3Acanal-components-sketch) — Irrigation and Drainage Engineering, chapter 3, asked 7×
- [Alignment factors and canal types](https://www.bctengineer.com/question.md?key=semester_6%2Firrigation_and_drainage_engineering%3Aalignment-factors-and-canal-types) — Irrigation and Drainage Engineering, chapter 3

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- [American vs European distribution layout in Nepal](https://www.bctengineer.com/question.md?key=semester_8%2Ftransmission_and_distribution_system_design%3Aamerican-vs-european-distribution-nepal) — Transmission and Distribution System Design, chapter 5, asked 2×
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