SS 2 First Term Agricultural Science Lesson Note – Drainage

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SUBJECT: AGRIC SCIENCE

TOPIC: DRAINAGE

CONTENT:

1. Meaning of Drainage
2. Types of Drainage
3. Importance of Drainage

SUB TOPIC 1: MEANING OF DRAINAGE

Drainage is the removal of excess water artificially from a farmland to prevent water logging and promote good farming activities. Excess water may be removed through channels, pipes or funnels either from the surface of land or beneath the soil.

 Types of Drainage (Drainage systems)

There are two major types of drainage. These are:

• Surface drainage
• Sub-surface / underground drainage.

Surface drainage: -This is the removal of excess water from the surface of the farmland using constructed open ditches, field drain, land grading and lateral ditches. This is divided into;

• Random field surface drainage
• parallel field drainage

Random field surface is suitable for areas with pot holes or depressions (rough topography).

Parallel field drain is ideal where fields are flat or less than 1 – 2% slope.

Advantages of Surface Drainage

1. It is easier to construct
2. It is cheaper than sub-surface drainage system

Disadvantage of surface Drainage

1. It disturbs the movement of machines like tractors.
2. It occupies large area of land that would have been used for cultivation.

 Sub-surface / underground Drainage.

This is an orderly removal of excess water beneath the soil from the land artificially using drainage tiles, pipes, moles and plastic tubing.

In this system, special drainage tiles made of porcelain or burnt clay are laid side by side with small openings between the adjacent tiles.

When the soil is saturated with water, the water is discharged through the openings between the adjacent tiles. Often, perforated tubings are used in place of ceramics because they are less expensive.

Types of Sub-surface drainage

There are different types of sub-surface drainage; they include:

• Random system
• Herringbone system
• Gridiron system
• The interception drains

(i)The random (natural) system is an undulating topography

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