---
title: "Short note: Sub-surface irrigation"
subject: "Irrigation and Drainage Engineering"
chapter: 1
key: "semester_6/irrigation_and_drainage_engineering:subsurface-irrigation-note"
source: https://www.bctengineer.com/q/semester_6/irrigation_and_drainage_engineering/subsurface-irrigation-note
site: BCT Engineering
---

# Short note: Sub-surface irrigation

Irrigation and Drainage Engineering · Chapter 1: Introduction

- Asked in: 2065 Kartik (old course), 4 marks
- Video: [SUB-SURFACE IRRIGATION](https://www.youtube.com/watch?v=-bug9zJgRvA) — Easy to Live
- 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/subsurface-irrigation-note
- Whole chapter: https://www.bctengineer.com/md/semester_6/irrigation_and_drainage_engineering/chapter-1

## Question

Write a short note on sub-surface irrigation.

## Short answer

Sub-surface irrigation supplies water to the root zone from below via a raised water table (natural) or buried perforated pipes (artificial). It suits permeable surface soil over an impervious layer 2-3 m down, flat land and low-salinity water. Advantages: low evaporation, no farm disruption; disadvantages: high cost, salt build-up and waterlogging risk.

## Answer

**Sub-surface irrigation** supplies water to the root zone from below the ground surface. The water table is raised or water is released below the surface so that it reaches the roots by capillary action.

#### Types
1. **Natural sub-irrigation:** the water table is naturally high, or seepage from canals or rivers keeps the root zone moist (e.g. low-lying river-bank lands).
2. **Artificial sub-irrigation:** water is fed through open ditches or buried perforated/porous pipes below the root zone; the water table is controlled by a gate or pump.

```text
  ground ----------------------------
  root zone
  ~~~~~~~ raised water table ~~~~~~~~
  o=o=o perforated pipe
  ===== impervious layer ===========
```

#### Conditions for success
- Permeable surface soil with an impervious layer 2-3 m below.
- Flat land and a good drainage outlet.
- Low-salinity water.

#### Merits
Little evaporation loss, no interruption of farm operations, no erosion, very efficient use of water.

#### Demerits
Costly installation, risk of salt build-up in the root zone, waterlogging if drainage is poor, and difficulty in maintenance.

## Check yourself

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

1. How does water reach roots in sub-surface irrigation?
   A. Spraying from above
   B. Surface flooding
   C. Capillary action from a raised water table
   D. Dripping onto leaves
   Answer: C. The water table is raised or water is released below the surface. (Key point: Mechanism)

2. Success requires:
   A. Steep slopes
   B. Highly saline water
   C. No impervious layer
   D. Permeable soil with impervious layer 2-3 m below, flat land, drainage outlet
   Answer: D. These conditions let the water table be controlled. (Key point: Conditions)

3. A merit of sub-surface irrigation:
   A. Little evaporation and no interruption of farm operations
   B. Low installation cost
   C. Easy maintenance
   D. Suits all soils
   Answer: A. It is efficient but costly. (Key point: Merit)

4. A demerit is:
   A. High evaporation
   B. Salt build-up in the root zone and waterlogging if drainage is poor
   C. Erosion
   D. Weeds on the surface
   Answer: B. Poor drainage causes salinity. (Key point: Demerit)

## Related in Irrigation and Drainage Engineering

- [Surface and sub-surface irrigation methods](https://www.bctengineer.com/question.md?key=semester_6%2Firrigation_and_drainage_engineering%3Asurface-subsurface-methods-suitability) — Irrigation and Drainage Engineering, chapter 1, asked 11×
- [Advantages of surface and sub-surface irrigation](https://www.bctengineer.com/question.md?key=semester_6%2Firrigation_and_drainage_engineering%3Asurface-subsurface-pros-cons) — Irrigation and Drainage Engineering, chapter 1
- [Surface methods and furrow irrigation](https://www.bctengineer.com/question.md?key=semester_6%2Firrigation_and_drainage_engineering%3Afurrow-irrigation-methods) — Irrigation and Drainage Engineering, chapter 1, asked 11×

## Related in other subjects

- [Control of sub-surface water and seepage](https://www.bctengineer.com/question.md?key=semester_6%2Ftransportation_engineering_i%3Asubsurface-drainage-measures) — Transportation Engineering I, chapter 4, asked 15×
- [Direct methods of sub-surface investigation](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Adirect-subsurface-methods) — Engineering Geology II, chapter 4, asked 3×
- [Surface versus sub-surface investigation](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Asurface-vs-subsurface-investigation) — Engineering Geology II, chapter 4, asked 3×
- [Surface versus sub-surface drainage](https://www.bctengineer.com/question.md?key=semester_6%2Ftransportation_engineering_i%3Asurface-vs-subsurface) — Transportation Engineering I, chapter 4, asked 2×