Meaning, Causes, Effects and Control of Erosion for JSS 1

Environmental Degradation: Erosion

Performance Objectives

By the end of the lesson, students should be able to:

1. state the meaning, types of erosion;
2. identify natural and human causes of erosion;
3. describe different methods of erosion control;
4. apply different methods of preventing erosion in the environment;
5. embark on a visit to erosion site.

Meaning of Erosion

Erosion is the wearing away and washing or blowing away of the topsoil by agents such as water and wind.

The topsoil is the uppermost layer of the earth. It is the most fertile part of the soil because it contains organic matter and essential nutrients that plants need to grow. When erosion occurs, this valuable layer is lost, leaving the land bare, rocky, and unproductive. This process is a major form of environmental degradation that affects agricultural land, roads, and buildings.

Types of Erosion

Erosion is classified based on the agent responsible for the movement of the soil. The two main types of erosion are water erosion and wind erosion.

1. Water Erosion

Water erosion occurs when rainfall, surface runoff, or flowing rivers wash away the soil. It is the most common type of erosion in tropical regions like Nigeria, especially in areas with heavy rainfall. Water erosion occurs in several stages, which include:

1. Splash Erosion: This is the first stage of water erosion. It occurs when raindrops fall directly onto bare, unprotected soil. The impact of the raindrops breaks down soil aggregates and splashes small soil particles into the air.
2. Sheet Erosion: This occurs when a thin, uniform layer of topsoil is washed away across a large area of land by surface runoff. It is often difficult to notice immediately because the soil is removed gradually and evenly.
3. Rill Erosion: As surface runoff concentrates, it begins to carve small, narrow channels into the soil. These small channels are called rills. Rills can easily be smoothed out during normal farming activities like ploughing.
4. Gully Erosion: This is an advanced and highly destructive stage of water erosion. It occurs when rills are left unchecked and grow wider and deeper. Gullies are large, deep channels that cannot be removed by ordinary farming equipment. Gully erosion is very common in the southeastern part of Nigeria, where it destroys roads, houses, and farmlands.

2. Wind Erosion

Wind erosion occurs when strong winds lift and blow away dry, loose, and fine soil particles. This type of erosion is most common in arid and semi-arid regions where there is very little rainfall and sparse vegetation cover. In Nigeria, wind erosion is highly prevalent in the northern states, such as Sokoto, Kano, Katsina, and Borno, especially during the dry season when the dry Harmattan winds blow across the region.

Causes of Erosion

Erosion is caused by both natural factors and human activities. Understanding these causes helps in planning effective control measures.

Natural Causes of Erosion

Natural causes are environmental factors that occur without human intervention. The main natural causes of erosion include:

1. Heavy Rainfall: High-intensity rainfall produces large volumes of surface runoff, which easily washes away loose soil particles.
2. Steep Slopes: Water flows much faster down steep hills and mountains. The high speed of the water increases its power to erode and carry away soil.
3. Strong Winds: In dry areas, strong winds easily lift and transport dry, loose topsoil that lacks vegetation cover.
4. Soil Type: Some soils, such as sandy soils, have loose particles that are easily washed or blown away compared to clay soils, which stick together more firmly.

Human Causes of Erosion

Human causes are activities carried out by people that expose the soil to erosion. The main human causes of erosion include:

1. Deforestation: This is the clearing or cutting down of forest trees without replanting them. Trees act as windbreaks, and their roots bind soil particles together. Removing trees leaves the soil bare and vulnerable to water and wind.
2. Overgrazing: This occurs when too many farm animals, such as cattle, sheep, or goats, feed on a particular piece of land for a long period. The animals eat up the grass and compact the soil with their hooves, making it easier for water to wash the soil away.
3. Bush Burning: Burning vegetation destroys the organic matter that binds soil particles together. It also removes the protective cover of the soil, exposing it directly to heavy rain and strong wind.
4. Poor Farming Practices: Farming methods such as ploughing up and down a slope instead of across the slope create paths for rainwater to flow quickly, leading to rill and gully formation.
5. Construction Activities: Building roads, houses, and factories involves clearing large areas of land and removing vegetation. If proper drainage systems are not constructed, runoff from roofs and paved surfaces can cause severe erosion.

Methods of Controlling and Preventing Erosion

Controlling erosion involves reducing the force of water and wind, protecting the soil surface, and binding soil particles together. The main methods of controlling and preventing erosion include:

1. Afforestation and Reforestation: Afforestation is the planting of trees in areas where there were no trees before, while reforestation is the replanting of trees in forests that have been cut down. Tree roots hold the soil firmly, and the leaves reduce the impact of raindrops on the soil.
2. Cover Cropping: This involves planting low-growing crops, such as melon, sweet potatoes, cowpea, or carpet grass, to cover bare soil. These crops act as a blanket that protects the soil from direct rainfall and wind.
3. Contour Ploughing: This is the practice of ploughing and planting crops across a slope rather than up and down the slope. The ridges created across the slope act as mini-dams that slow down surface runoff.
4. Terracing: This involves cutting step-like platforms into very steep hillsides. Terraces reduce the speed of water flowing down the slope, allowing the water to soak into the soil rather than washing it away.
5. Building Drainage Channels: Constructing concrete gutters and drainage channels helps to collect and direct rainwater safely away from buildings, roads, and farmlands into nearby streams or rivers.
6. Windbreaks (Shelterbelts): Planting rows of tall trees or shrubs around farmlands helps to block and reduce the speed of strong winds, thereby preventing wind erosion.
7. Avoiding Bush Burning: Preserving dry vegetation cover helps to maintain soil structure and organic matter, keeping the soil resistant to erosion.

Practical Application: Preventing Erosion in the School and Home Environment

Preventing erosion is a practical task that can be carried out around school buildings, playgrounds, and home compounds. One of the most effective ways to prevent erosion on bare ground is by planting carpet grass or cover crops.

How to Plant Carpet Grass to Prevent Soil Erosion

The required materials are:

1. Carpet grass sods or sprigs
2. Hand trowels or small hoes
3. Watering cans filled with water
4. Organic manure or compost

The procedure involves the following steps:

1. Identify a bare patch of land in the school or home compound that is prone to water erosion.
2. Clear any weeds, stones, or debris from the selected area.
3. Use a hand trowel or small hoe to loosen the topsoil to a depth of about 5 to 10 centimetres.
4. Mix organic manure or compost into the loosened soil to improve soil fertility and structure.
5. Place the carpet grass sprigs or sods onto the prepared soil, pressing them down firmly so that the roots make good contact with the soil.
6. Water the planted grass immediately using a watering can.
7. Water the grass regularly, especially during the first two weeks, until the roots are well established and the grass covers the bare ground.

Field Activity: Visit to an Erosion Site

A visit to a local erosion site helps learners observe the real-world effects of environmental degradation and identify the causes and possible control measures.

Guidelines for the Field Visit

Important safety tips and instructions include:

1. Safety First: Students must wear sturdy shoes and protective clothing. Do not stand too close to the edges of deep gullies, as the soil can collapse suddenly. Always stay with the teacher or guide.
2. Observation: Look closely at the eroded area. Identify the type of erosion (sheet, rill, or gully). Observe the depth and width of any channels.
3. Identifying Causes: Look around the site to determine what might have caused the erosion. Is the land bare? Are there drainage channels? Is the slope steep? Are there signs of human activities like construction or deforestation?
4. Recording: Take notes, draw sketches, or take photographs of the erosion site. Record the location, date, and key observations.
5. Reporting: Write a brief report describing the site, the observed damage, the likely causes, and recommendations for controlling the erosion.

Summary and Evaluation

Review Questions

The following questions can be used to assess understanding of the topic:

1. Explain the meaning of soil erosion.
2. State two main types of erosion and describe three stages of water erosion.
3. List three natural causes and three human causes of soil erosion.
4. Outline four methods that can be used to control or prevent erosion in a farming community.
5. Describe the steps involved in planting cover crops or grass to protect bare soil in a school compound.