Lesson Notes By Weeks and Term - Junior Secondary School 2

SUBJECT:� BASIC SCIENCE ��� ���

CLASS:� JSS2

DATE:

TERM: 3RD TERM

REFERENCE

• Precious Seed BASIC SCIENCE FOR JUNIOR SECONDARY SCHOOLS BOOK 2

�

WEEK SEVEN

ENVIRONMENTAL HAZARD 1 (Erosion and Flooding)

Introduction

Environmental hazard are the damages that occur when the natural resources such as land, forest etc., are denatured, that is, when they are affected by some external factors such as soil erosion, flooding, bush burning, deforestation, desertification, dpletion of ozone layer etc, they loose their natural properties.

�

Soil erosion

Soil erosion is the removal of soil by water, wind and other agents. There are two major factors which contribute to holding the particles of soil firmly together. They are:

1. The clay content of the soil: soil varies from place to place but all soils have certain properties in common.
2. Another important factor is the roots of `the vegetation covering the soil.

�

Human activities that causes soil erosion

1. Careless cultivation
2. Bush burning
3. Industrialization
4. Expansion of urban areas
5. Highway construction

�

Methods of controlling soil erosion

1. Planting cover crops

Cover crops are so known because they cover the soil evenly by not allowing rain to fall directly on the soil.

1. Strip cropping :This involves alternating row crops like maize or cassava with cover crops such as beans, cowpea or grass.
2. Mulching

This is a control measure employed by using dry grass to cover ridges ans mounds on the farm.

1. Planting of trees and grass

Trees and grass serve as wind breaks; the roots of the plants also help to hold soil particles together against the action of rain and wind.

1. Making ridges along slopes

Soil erosion can also be controlles by making ridges and planting crops along the slope of a hill

1. Terracing : On steep slopes, the most effective method is to construct terraces (a series of ridges or steps that resemble a staircase) to reduce the speed of water and thus prevent erosion.

�

EVALUATION

1. Define environmental hazard
2. State three methods of controlling erosion.

�

Flooding

Flooding occurs when excess amount of water covers a particular area that is not usually covered with water.

�

Causes of flood

1. Amount of rain: Excessive rainfall may cause flooding because water runs off the land in quantities that cannot be carried in stream channels
2. Establishment of settlements along river channels: Some areas are of rivers and other bodies of water such as the flood plains are sometimes filled with sand and used for development purposes.
3. Strong tidal waves

Tidal waves can be low or high depending on the time and season of the year.

1. Dumping of refuse which may block culverts or water channels.
2. Presence of steep slopes in an area.
3. Inadequate or poor urban planning.
4. Breakdown of dams and embankments.

�

Drainage pattern

1. Surface drainage
2. Sub-surface drainage

�

Prevention of flooding

1. Public enlightenment on effects of flooding
2. Construction of dams and levees to act as flood reservoirs.
3. Construction of wider gutters or culverts.
4. Disallowing indiscriminate dumping of refuse.
5. Regular clearance of drainage channels to prevents blockage
6. Prevention of the erection of buildings in swampy areas or along water paths.

�

EVALUATION

1. Define flooding.
2. State three causes of flooding.

�

GENERAL EVALUATION

1. Define environmental hazard
2. State three methods of controlling erosion.
3. Define flooding.
4. State three causes of flooding.

�

WEEKEND ASSIGNMENT

1. Soil ---------is the removal of soil by water, wind and other agents. A. erosion B. land C. water D. evacuation
2. Excessive rainfall may cause ---------because water runs off the land in quantities that cannot be carried in stream channels A. erosion B. flooding C. evacuation D. tanning
3. Construction of dams and levees to act as flood-----------. A. tank B. culvertt C. reservoirs D. nonagons
4. ----------occurs when excess amount of water covers a particular area that is not usually covered with water. A. Camping B. Storming C. Drilling D. Flooding
5. Excessive ----------may cause flooding because water runs off the land in quantities that cannot be carried in stream channels A. rainfall B. drainage C. flooding D. control

�

THEORY

1. Define flooding
2. State three ways by which flooding can be controlled

�

REFERRENCE

CLASSIC BASIC SCIENCE FOR JUNIOR SECONDARY SCHOOL 3 PAGES 20-29