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Lesson Note

Subject: BST

Topic: Environmental Harzards I

Subtopic: Soil Erosion

Class: JS3

Term: First

Objectives: By the end of the lesson, the learners should be able to:

  1. Define the term Environmental Harzards;
  2. Mention the types of Environmental Harzards;
  3. Define Soil Erosion;
  4. State the causes of soil erosion;
  5. State the effects of soil erosion;
  6. State ways by which soil erosion can be controlled or prevented.

Lesson Summary/Discussions

Period 1: Meaning And Types of Environmental Hazards
Environmental hazard is the state of events which has the potential to threaten the surrounding natural
environment and adversely affect people’s health.
A hazard is any biological, chemical, mechanical, environmental or physical agent that is reasonably likely to cause harm or damage to humans, other organisms or the environment in the absence of its control.

Types of Environmental Harzards

There are different types of environmental harzards, these include:
Bush burning

Period 2: Soil Erosion
Erosion is the wearing or washing away of the top soil and sub-soil from the land either by water or wind.

Types of Erosion
There are different types of erosion which include:

  1. Sheet Erosion
  2. Rill Erosion
  3. Gully Erosion
  4. Wind Erosion
  5. Sheet Erosion

These are discussed below:

Sheet Erosion

This is the washing away of topsoil layer. Soil particles are detached or displaced by falling raindrops
and carried from their original location.

Rill Erosion
This is very common in cultivated land where the surface is not even. Rainwater accumulates in the
depressions of these paths.
Gully Erosion
This occurs when the surface of water cuts so deeply that the soil cannot be smoothened by ordinary tillage tools.
Wind Erosion
This reaches the greatest proportion in semi-arid and arid regions and much damage is done to soil when soil is blown from one place to another leaving the former unproductive.

Causes of Erosion

  1. Building and Construction: Building of houses, industries, markets and road construction make the soil loose its fertility and prone to erosion.
  2. When there is low development, a lot of trees are felled due to the construction of new roads. This is usually done with very heavy machinery which will not only affect he soil but also expose the soil to some agents of erosion.
  3. Over grazing of grasses on a particular area.
  4. Deforestation.
  5. Desertification.
  6. Some other human activities which involves constant and rigorous work on a particular area.

Effects of Erosion

  1. It is destructive of all forms of soil types.
  2. It reduces soil fertility.
  3. It damages road and soil surfaces.
  4. It can lead to a collapse of building walls.
  5. The soil carried away may lead to leaching.
  6. Gully erosion renders the field irregular this lead to a great inconvenience and loss of efficiency in cultivation.

Ways of Controlling/Preventing Erosion

  1. Mulching, in which cut grasses or crop residues, are spread over the soil surface under a growing crop. It retains moisture, reduces
  2. weeds and prevents the exposure of the soil surface thereby reducing soil erosion.
  3. Avoid overgrazing.
  4. Avoid bush burning.
  5. Public education and awareness.
  6. Afforestation (planting of trees).
  7. Planting of cover crops, which help to cover the soil and prevent them from being exposed to agents of erosion.
  8. Sloping lands can be protected by the construction of terraces ploughing along the contours, planting on ridges and channeling water run-off along grassed water ways or ditches.

Done studying? See previous lessons in BST

Lesson Evaluation/ Test

  1. Define the term Environmental Harzards.
  2. Mention the types of Environmental Harzards.
  3. Define Soil Erosion.
  4. What are the causes of soil erosion?
  5. What are the effects of soil erosion?
  6. State ways by which soil erosion can be controlled or prevented.

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