---
title: "Factors in deciding canal alignment"
subject: "Irrigation and Drainage Engineering"
chapter: 3
key: "semester_6/irrigation_and_drainage_engineering:canal-alignment-factors"
source: https://www.bctengineer.com/q/semester_6/irrigation_and_drainage_engineering/canal-alignment-factors
site: BCT Engineering
---

# Factors in deciding canal alignment

Irrigation and Drainage Engineering · Chapter 3: Canal Irrigation System

- Asked in: 2079 Chaitra, 5 marks
- Video: [Canal Alignment Irrigation Engg By Smita mishra panigrahi (Ex-IES)](https://www.youtube.com/watch?v=rPtLwzUx4JY) — CGPSC CGVYAPAM PANIGRAHI'S CIVIL ENGG FOUNDATION 
- 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-alignment-factors
- Whole chapter: https://www.bctengineer.com/md/semester_6/irrigation_and_drainage_engineering/chapter-3

## Question

What factors do you consider while deciding a canal alignment?

## Short answer

Canal alignment follows the highest ground (ridge) for maximum command area by gravity. It minimizes earthwork by staying near balancing depth, avoids costly cross-drainage works, and selects stable geology. Alignment uses gentle curves, avoids villages and fertile land, reduces land acquisition costs, and provides required head with few drops.

## Answer

The alignment should give the maximum command at minimum cost and be safe. The factors are:

1. **Command:** keep the canal on the highest ground (watershed/ridge) so that gravity irrigation covers the largest area, with the full supply level above the field levels.
2. **Topography and contours:** avoid unnecessary deep cuttings and high fillings; follow the ground slope as far as possible; keep near the balancing depth for economy of earthwork.
3. **Cross-drainage works:** keep the number of drainage crossings (aqueducts, culverts) to a minimum, as each is costly.
4. **Geology and soil:** avoid rocky, sandy, porous or landslide-prone areas, and saline or swampy ground.
5. **Straight and smooth alignment:** avoid sharp bends (use curves of radius at least 5 times the bed width), and avoid cutting through villages and fertile land.
6. **Land acquisition and existing structures:** avoid roads, houses and religious places, to keep compensation low.
7. **Head and drops:** the length and bed slope should provide the needed head with the fewest falls.
8. **Command and field boundaries:** align along property boundaries; avoid splitting farms.
9. **Future extension and drainage:** allow for extension and avoid waterlogging.
10. **Accessibility** for construction and O&M, and nearness of construction material (borrow area).

## Check yourself

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

1. Why is the canal placed on the highest ground?
   A. So gravity irrigation covers the maximum area with FSL above field levels
   B. To reduce lining cost
   C. To avoid bridges
   D. To increase silt
   Answer: A. Ridge alignment gives maximum command. (Key point: Command)

2. Why minimise drainage crossings?
   A. They increase command
   B. Each aqueduct, siphon or culvert is costly
   C. They reduce seepage
   D. They raise water level
   Answer: B. Fewer crossings reduce cost. (Key point: Cross-drainage)

3. What is advised for bends?
   A. Use sharp bends to save length
   B. Radius equal to bed width
   C. Avoid sharp bends; radius at least 5 times bed width
   D. Radius of 1 m
   Answer: C. Gentle curves keep the flow smooth and banks safe. (Key point: Curves)

4. Which areas should be avoided?
   A. Fertile alluvial plains only
   B. Ridge lines
   C. Clay soils only
   D. Rocky, sandy, porous, landslide-prone, saline or swampy ground
   Answer: D. Such ground causes seepage, failure or damage. (Key point: Soil and geology)

## Related in Irrigation and Drainage Engineering

- [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
- [Why a canal fall; site selection factors](https://www.bctengineer.com/question.md?key=semester_6%2Firrigation_and_drainage_engineering%3Acanal-fall-purpose-site-selection) — Irrigation and Drainage Engineering, chapter 7
- [Canal in alluvium, Q 64, d 0.5 mm](https://www.bctengineer.com/question.md?key=semester_6%2Firrigation_and_drainage_engineering%3Aalluvial-canal-q64-d05mm) — Irrigation and Drainage Engineering, chapter 4
- [Possible alignments of an irrigation canal](https://www.bctengineer.com/question.md?key=semester_6%2Firrigation_and_drainage_engineering%3Acanal-alignment-types-sketch) — Irrigation and Drainage Engineering, chapter 3, asked 5×

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