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Lesson Note

Subject: BST

Topic: Environmental Harzards II

Subtopic: Flooding and Deforestation

Class: JS3

Term: first

Period 3: Flooding

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

  1. Define the term flooding;
  2. State three causes of flooding;
  3. Mention five effects of flooding;
  4. Suggest ways by which flooding can be prevented or controlled.

Flooding can be defined as incident which occurs when a part of the soil or land is submerged under water. Some of lands are prone to flooding. This is due to the soil structure.

Causes of Flooding

The following reasons have long been identified as why we have flooding:

  1. People build houses or some other structures across the drainage systems thereby blocking the normal flow of water and causing flood.
  2. The overflowing of water from dams (built by the government to supply electricity) when there is a heavy down pour.
  3. Land filling which tends to displace water from its level.

Effects of Flooding
The effects of flooding include:

  1. It damages houses and other properties.
  2. It can destroy lives.
  3. It softens a house foundation.
  4. It can increase the spread of diseases.
  5. It makes soil infertile by reducing soil nutrients.
  6. It reduces the available land for cultivation of crops.

Ways of Preventing Flooding
Some of the ways of preventing flooding include:

  1. Building or construction of canals or adequate drainages by the government or individuals
  2. especially in areas with impervious rock layers close to the surface.
  3. Proper drainage ( dredging) ol rivers especially where dams are built.
  4. Preventing the building or construction of roads, houses, etc. across canals or drainages.
  5. In extreme cases, building or erecting walls along the banks of rivers.
  6. Mulching
  7. Sand filling low lands.


  1. Define the term flooding.
  2. What are the causes of flooding?
  3. Mention five effects of flooding.
  4. In what ways can flooding be prevented or controlled?

Done studying? See previous lessons in BST or proceed to next lesson.

Period 4: Environment Harzards III

Subtopic: Deforestation

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

  1. Define the term deforestation;
  2. State the causes of deforestation;
  3. State the negative effects of deforestation;
  4. State the positive effects of deforestation;
  5. Suggest ways of preventing or controlling deforestation;
  6. Identify the need for forest conservation.

Lesson Content

Deforestation can be defined as the process of cutting down trees in a large area and the destruction of forests by people.
It is also the clearance of naturally occurring forests by the processes of logging and/or burning of trees in a forested area.

  1. Corruption of government institutions.
  2. The inadequate distribution of wealth and power.
  3. Population growth and over population.
  4. Urbanization, infrastructural development.
  5. Economic gains (greed), since forest conversion has been viewed by some as more profitable than forest conservation.
  6. Cattle ranching and overgrazing
  7. Over heavy logging and commercial agriculture.
  8. Acid rain and building of dams.
  9. The race to produce some scarce fruits such as spices, sugar, tobacco and clothes.
  10. Globalization (in some cases) since it has promoted localized forest recovery.

Effects of Deforestation

People’s removal of trees without sufficient reforestation has always resulted to negative effects such as: damage to habitat, biodiversity (loss of Living things – plants and animals) and aridity. Deforested regions typically incur significant adverse soil erosion, flooding, land slide, famine and frequently degrade into wasteland.

Research has shown that deforestation is a contributor to global climatic change leading to global warming and is often cited as one of the major causes of the enhanced green house effects. Tropical deforestation is also
responsible for approximately 20% of the world green house gas emission. Deforestation mainly in tropical areas
account for up to one-third of the total carbon (iv)OXide (CO) emission.
Trees and other plants remove carbon in the form of CO, from the atmosphere during the process of
photosynthesis and release Oxygen back into the atmosphere during normal respiration. The decay and
burning of wood on the other hand releases much of this stored carbon back to the atmosphere, therefore, for the forests to take up carbon, the wood must be harvested and turned into long-lived products and trees must be replanted.
Forests are stores of carbon and can be either sinks or sources depending upon environmental circumstances.
Deforestation may cause carbon stores held in soil to be released. Mature forests alternate between being net sinks and net sources of CO. The incineration and burning of forest plants in order to clear land releases tonnes of CO, which contributes to global warming.

Deforestation can also affect water cycle by reducing the forest whose roots are supposed to absorb water
(ground waler) and eventually release them to the atmosphere (evaporation). So, this makes the climate drier. This also reduces the content of water in the soil (ground waler) as wcll as atmospheric moisture.
Some other negative effects of deforestation include:

  • Reduction of soil moisture via transpiration.
  • Creation of large pores in the soil.
  • Affects precipitation.
  • Slows down surface runoff.
  • Decline or loss in forest and its products.
  • Destruction of genetic variations (crop resistance).
  • Illegal logging which causes loss of billions of naira to national economics.

Some posifive effects of deforestation nclude:

  • Developed countries continue to utilise timber for building houses and wood pulp for paper.
  • Over three billion people rely on wood for cooking, heating, furnilure.
  • Wood is also used in building.

Regulation/Prevention and Control of Deforestation
Some ways of controlling deforestation include:

  1. Farming: New methods are being developed to farm more intensively, such as high yield hybrid crops. green house, autonomous building gardens and hydroponics. These methods are often dependent on chemical inputs to maintain necessary yield. Cattle are now grazed on farmland that is resting and rejuvenaing, this is experienced in cyclic agriculture. This cyclic agriculture actually increases the fertility of the soil.
  2. Forest plantation: Certificate of sustainable forest management practice.
  3. Reforestation: Replacing trees where they were originally placed.
    Afforestation: Planting trees where they have not existed before.
  4. Forest management: Efforts have been attempted on conserving the forest for many centuries because it has long been known that delorestation can cause environmental damage Sulficiently.
  5. Using alternative source of heat instead of wood.
  6. Checking desert encroachment by irrigation

Need for conserving Our Forest
Trees matter because about 50 million creatures, 50%- 90% of all organisms, 90% of our relatives, the primates
can live no place but the rich rainforests. Not only are other specics at risk when trees are destroycd, but the human race also benefits from what the trees give.
From something as minor as the spices that is used in cooking to life giving medicines; the rainforests amplify and save lives. 25% of medicinces come from the forests.
The forests give life not only to other species, but they help to prolong the human race. The trees help to purify the air that we breathe in; they also determine rainfall and replenish the atmosphere.
It is important to note that Irees help to cool or regulate the earth s climate. Such valuable services help to prevent erosion, landslicles and making the most food production.
Once the soil temperature exceeds 25°C, volatile nutrients, ingredients like nitrogen can be lost, further
reducing the fertility of the remaining soil.
Tree roots bind soil together, and if the soil is sufficiently shallowed, they act to keep the soil in place by binding with underlying bedrock. Free removal on steep slopes with shallow soil increases the risk of landslides which can threaten people living nearby.
In some cases however, deforestation only affects the trunks of trees, allowing the roots to stay rooted.
Moreover, forests are able to extract carbon (iv) oxide (CO) and pollutant from the air, thus contributing to
stability of biosphere.
Done studying? See previous lessons in BST


  1. Define the term deforestation.
  2. State the causes of deforestation.
  3. What are the negative effectls of deforestation?
  4. State the positive effects of deforestation.
  5. Suggest ways of preventing or controlling deforestation.
  6. There is the need for forest conservation: Discuss.

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