Lesson Notes By Weeks and Term v3 - Junior Secondary 3
Environmental Hazards I
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Environmental Hazards I
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Subject: Basic Science
Class: Junior Secondary 3
Term: 1st Term
Week: 5
Theme: Learning About Our Environment
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explain soil erosion; identify human activities that cause erosion; describe methods of controlling erosion; describe practical methods of preventing erosion on a given farm-land; describe different types of drainage patterns in the ir community, state the causes of flooding; describe how flooding can be prevented; discuss effects of flooding.
rainfall.
How Flooding Can Be Prevented: Prevention strategies aim to manage water flow and protect vulnerable areas.
1. Efficient Drainage Systems: Constructing and regularly maintaining (clearing of debris, dredging) effective networks of gutters, canals, and culverts to channel rainwater away quickly.
Example: Developing robust storm drain infrastructure in urban centres.
2. Construction of Dams and Levees (Embankments): Dams: Built across rivers to create reservoirs that store excess water during heavy rainfall, releasing it gradually.
Levees/Dykes: Earthen or concrete barriers built along riverbanks to prevent water from overflowing onto adjacent land.
3. Afforestation/Reforestation: Planting trees, especially in upper catchment areas, helps increase water infiltration into the soil, reduces surface runoff, and stabilises soil.
4. Proper Waste Management: Implementing effective waste collection and disposal systems to prevent refuse from blocking drainage channels. Community involvement in keeping gutters clean is vital.
5. Urban Planning and Zoning: Restricting construction in flood-prone areas (floodplains), designating such areas for parks or agriculture, and ensuring new developments incorporate sustainable drainage solutions.
6. River Dredging: Removing silt and sediment from riverbeds to increase their capacity to carry water, reducing the likelihood of overflow.
7. Early Warning Systems: Establishing systems to monitor weather patterns and river levels, providing timely alerts to communities in flood-prone areas, allowing for evacuation and preparedness.
Effects of Flooding: The impacts of flooding are usually devastating and wide-ranging:
1. Loss of Lives and Property: Flooding can directly cause drownings and collapse buildings, leading to fatalities and destruction of homes, businesses, and personal belongings.
2. Displacement of People: Communities are forced to evacuate their homes, leading to large numbers of internally displaced persons (IDPs) and strain on temporary shelters.
3. Damage to Infrastructure: Roads, bridges, electricity poles, communication networks, and water supply systems are often destroyed or damaged, disrupting essential services and connectivity.
4. Destruction of Crops and Livestock: Farmlands are submerged, crops are washed away or rot, and livestock may drown, leading to food shortages and economic losses for farmers.
5. Spread of Diseases: Stagnant floodwaters create breeding grounds for mosquitoes (malaria) and can contaminate water sources, leading to outbreaks of waterborne diseases like cholera, typhoid, and dysentery.
6. Environmental Pollution: Floodwaters can carry pollutants from waste dumps, sewage systems, and industrial sites, spreading contamination across wider areas.
7. Economic Disruption: Businesses shut down, transport is halted, and agricultural production is affected, leading to significant economic losses and increased poverty.
8. Psychological Trauma: Survivors often experience stress, anxiety, and trauma due to loss, displacement, and the frightening experience of flooding. --- This section provides a detailed explanation of the core concepts related to soil erosion, drainage patterns, and flooding.
A. Soil Erosion Definition: Soil erosion is the process by which the top layer of soil, which is often the most fertile, is detached and transported from one place to another by natural agents like water and wind, or through human activities. This process leads to land degradation, reduced agricultural productivity, and various environmental problems.
Human Activities That Cause Erosion: Human actions often accelerate natural erosion processes.
Key activities include:
1. Deforestation: The cutting down of trees and vegetation without adequate replanting removes the protective cover that binds the soil with their roots. This exposes the soil directly to the impact of rain and wind, making it susceptible to erosion.
Example: Extensive logging in tropical rainforests or clearing land for agriculture in states like Cross River or Taraba.
2. Overgrazing: Allowing livestock (cattle, goats, sheep) to feed on vegetation excessively in a confined area removes the grass cover, compacts the soil, and exposes it to erosion.
Example: Overgrazing by herdsmen in the Sahelian regions of Northern Nigeria, leading to desertification.
3. Poor Farming Practices: Bush Burning: Burning vegetation residues after harvest destroys organic matter in the soil, kills microorganisms, and leaves the soil bare and unprotected.
Tilling/Ploughing Up and Down Slopes: This creates channels that funnel water rapidly downhill, increasing its erosive power and leading to gully formation.
Monoculture: Planting the same crop repeatedly can deplete specific nutrients and reduce soil structure, making it more vulnerable to erosion compared to diverse cropping systems.
Intensive Cultivation: Continuous farming without allowing the land to recover or replenish nutrients can degrade soil structure.
4. Construction and Urbanisation: Construction activities involve clearing vegetation, excavating land, and creating large areas of impervious surfaces (concrete, tarmac). This increases surface runoff and removes soil cover, leading to erosion.
Example: Rapid urban expansion in cities like Lagos and Abuja, where hills are levelled and vegetation removed for housing estates and roads.
5. Mining Activities: Open-cast mining, particularly for solid minerals, involves removing large quantities of topsoil and subsoil, significantly altering the landscape and exposing underlying layers to erosion.
Example: Tin mining in Jos Plateau or coal mining in Enugu in the past, causing widespread land degradation.
Methods of Controlling Erosion: These methods aim to protect the soil from the direct impact of erosive agents and slow down water movement.
1. Afforestation/Reforestation: Planting new trees (afforestation) or replanting trees in deforested areas (reforestation) helps to restore vegetation cover. Tree roots bind the soil, their canopy reduces the impact of raindrops, and their leaves add organic matter to the soil.
Example: Government initiatives to plant trees in arid zones of Nigeria to combat desertification.
2. Contour Ploughing: This involves ploughing or tilling across the slope, following the contours of the land, rather than up and down. The furrows created act as small dams, slowing down water runoff and allowing more water to infiltrate the soil.
Example: Farmers in hilly regions of Plateau or Ondo states adopting this practice.
3. Terracing: This method is used on steep slopes where flat steps or benches are cut into the hillside. Each terrace has a slight slope inwards to allow water to collect and infiltrate, preventing it from rushing down the entire slope.
Example: Common in mountainous regions for growing crops like rice.
4. Strip Cropping: This involves cultivating different crops in alternating strips along the contours of the land. Typically, a strip of erosion-resistant crop (e.g., grass, fodder crops) is alternated with a strip of erosion-prone crop (e.g., maize, beans). The erosion-resistant strips trap soil and slow water flow.
Example: Integrating maize with leguminous cover crops in parts of Northern Nigeria.
5. Gully Control: Gullies are severe forms of erosion.
Control methods include: Gabions: Wire mesh cages filled with rocks, used to build check dams within gullies to slow down water, trap sediment, and stabilise the gully.
Check Dams: Small barriers made of stones, logs, or concrete built across gullies to reduce the velocity of water flow. * Vegetation Planting: Planting trees, shrubs, and grasses along the banks and base of erosion-resistant strips trap soil and slow water flow.
Example: Integrating maize with leguminous cover crops in parts of Northern Nigeria.
5. Gully Control: Gullies are severe forms of erosion.
Control methods include: Gabions: Wire mesh cages filled with rocks, used to build check dams within gullies to slow down water, trap sediment, and stabilise the gully.
Check Dams: Small barriers made of stones, logs, or concrete built across gullies to reduce the velocity of water flow.
Vegetation Planting: Planting trees, shrubs, and grasses along the banks and base of gullies to stabilise the soil.
6. Mulching: Covering the soil surface with organic materials (e.g., straw, dry leaves, wood chips, crop residues) or inorganic materials (e.g., plastic sheets). Mulch protects the soil from rain impact, reduces evaporation, suppresses weeds, and adds organic matter as it decomposes.
Example: Used in market gardens or smaller farms to conserve moisture and prevent erosion.
7. Proper Land Use Planning: Developing and enforcing regulations on where and how land can be used, ensuring sensitive areas (e.g., steep slopes, riverbanks) are protected or used sustainably. Practical Methods of Preventing Erosion on a Given Farmland: For a typical Nigerian farmland, practical prevention methods include:
1. Crop Rotation: Alternating different types of crops in the same field over successive seasons. This helps maintain soil fertility, structure, and organic matter content, making the soil more resistant to erosion. For instance, rotating root crops with cereals and legumes.
2. Cover Cropping: Planting non-cash crops (e.g., legumes like Mucuna, Centrosema) specifically to cover the soil, especially during fallow periods or between main crops. Cover crops protect the soil from rain and wind, add organic matter, and improve soil structure.
3. Minimum Tillage/No-Till Farming: Reducing the amount of soil disturbance during planting. Instead of extensive ploughing, seeds are planted directly into undisturbed soil, often through the previous crop residues. This leaves organic matter on the surface, protecting the soil.
4. Terracing/Contour Bunding: For farms on slopes, constructing small earthen or stone bunds (barriers) along the contours to trap water and soil.
5. Hedgerow Intercropping (Alley Cropping): Planting rows of fast-growing nitrogen-fixing trees or shrubs (hedgerows) between which crops are grown. The hedgerows provide biomass for mulching, reduce wind speed, and their roots stabilise the soil.
B. Drainage Patterns Definition: Drainage patterns refer to the geometric arrangement of streams, rivers, and their tributaries within a drainage basin (or watershed). The pattern is influenced by the underlying geology, topography, climate, and vegetation of a region. Types of Drainage Patterns in Nigerian Communities:
1. Dendritic Pattern: Description: This is the most common drainage pattern, resembling the branching structure of a tree or a human circulatory system. Tributaries join larger streams at acute angles.
Characteristics: It typically develops in areas where the underlying rock or soil is uniform in resistance to erosion, meaning there are no strong structural controls guiding the water flow.
Occurrence in Nigeria: Widely observed in many parts of Nigeria, especially in regions with relatively uniform sedimentary rocks or crystalline basement rocks, such as the Niger Delta, parts of the Benue Trough, and the Basement Complex regions where erosion acts uniformly.
Visual Aid: [Teacher can draw a simple tree-like diagram on the board.]
2. Parallel Pattern: Description: Streams and rivers flow in roughly parallel lines, often separated by uniform interstream distances.
Characteristics: This pattern typically develops on uniformly sloping surfaces, such as coastal plains, escarpments, or long, parallel ridges. The underlying geology might have parallel features or the land might have a consistent gradient.
Occurrence in Nigeria: Can be observed in areas with coastal plains (e.g., parts of Lagos and Ogun states near the coast) or along scarplands where there's a strong geological trend.
Visual Aid: [Teacher can draw several parallel lines with smaller tributaries joining them at acute angles.]
3. Trellis Pattern: Description: A rectangular drainage pattern where tributaries join the main stream at nearly right angles (90 degrees). The main streams flow parallel to each other. * Characteristics: This pattern is characteristic of folded mountainous regions or areas with alternating bands of resistant and less resistant rock strata (e.g., anticlines and synclines). plains (e.g., parts of Lagos and Ogun states near the coast) or along scarplands where there's a strong geological trend.
Visual Aid: [Teacher can draw several parallel lines with smaller tributaries joining them at acute angles.]
3. Trellis Pattern: Description: A rectangular drainage pattern where tributaries join the main stream at nearly right angles (90 degrees). The main streams flow parallel to each other.
Characteristics: This pattern is characteristic of folded mountainous regions or areas with alternating bands of resistant and less resistant rock strata (e.g., anticlines and synclines). Rivers flow along valleys formed in less resistant rocks.
Occurrence in Nigeria: Less common as a dominant pattern across large areas, but elements might be seen in specific regions with folded or faulted structures, such as parts of the Adamawa Highlands or the Mambilla Plateau.
Visual Aid: [Teacher can draw a grid-like pattern with main streams and tributaries joining at right angles.]
4. Radial Pattern: Description: Streams flow outwards in all directions from a central high point, such as a volcanic cone, isolated hill, or dome-shaped uplift.
Characteristics: The drainage radiates like the spokes of a wheel from a central elevated feature.
Occurrence in Nigeria: Can be observed around isolated inselbergs (e.g., Zuma Rock vicinity), or around some hills in the Jos Plateau, though not a major regional pattern.
Visual Aid: [Teacher can draw a central point with lines radiating outwards.] Teachers should encourage students to observe and identify which patterns are most common in their local communities, relating them to local topography and land use.
C. Flooding Definition: Flooding occurs when an area or land that is normally dry becomes submerged under water. It is a natural event but can be exacerbated by human activities and climate change.
Causes of Flooding:
1. Heavy and Prolonged Rainfall: Intense or continuous rainfall exceeding the infiltration capacity of the soil and the capacity of drainage systems leads to excessive surface runoff and river overflow.
Example: The annual rainy season in Nigeria often brings heavy rainfall, especially in coastal regions and riverine areas.
2. Blocked Drainage Systems: Accumulation of refuse, debris, and silt in gutters, canals, and urban drainage channels prevents water from flowing freely, causing it to overflow onto streets and homes.
Example: Common problem in Nigerian cities like Lagos and Port Harcourt due to poor waste management.
3. River Overflow: When rivers swell due to heavy upstream rainfall or melting snow (not applicable in Nigeria), they can exceed their bank capacity and inundate surrounding floodplains.
Example: The annual flooding of communities along the Niger and Benue Rivers.
4. Dam Failure/Overflow: Collapse of a dam or the intentional release of water from a dam when its reservoir reaches critical levels can lead to sudden, large-scale downstream flooding.
Example: The Lagdo Dam in Cameroon has historically caused significant flooding in Nigeria's Benue River Basin when its gates are opened.
5. Storm Surges: In coastal areas, strong winds associated with storms (e.g., hurricanes, cyclones, though less direct impact in Nigeria, coastal storm systems do occur) can push seawater onshore, causing coastal flooding.
Example: Parts of the Niger Delta coastline are vulnerable to storm surges.
6. Deforestation: Removal of forests reduces the land's ability to absorb rainwater. Forested areas act like sponges, retaining water; without them, runoff increases significantly.
7. Building on Floodplains: Construction on natural floodplains (areas adjacent to rivers that are naturally prone to flooding) obstructs water flow and places human settlements in harm's way.
8. Tidal Surges/High Tides: In low-lying coastal areas, exceptionally high tides can cause localized flooding, especially if combined with heavy rainfall.
How Flooding Can Be Prevented: Prevention strategies aim to manage water flow and protect vulnerable areas.
1. Efficient Drainage Systems: Constructing and regularly maintaining (clearing of debris, dredging) effective networks of gutters, canals, and culverts to channel rainwater away quickly.
Example: Developing robust storm drain infrastructure in urban centres.
2. Construction of Dams and Levees (Embankments): Dams: Built across rivers to create reservoirs that store excess water during heavy rainfall, releasing it gradually. * Levees/Dykes: Earthen or concrete barriers built along riverbanks to prevent water from overflowing onto adjacent land.
Community Environmental Action: Students can apply their understanding by participating in or advocating for local environmental protection initiatives. For instance, during "Environmental Sanitation Days" in their communities, they can actively clear blocked gutters, plant trees in erosion-prone areas, or educate neighbours on proper waste disposal to prevent drainage blockages and subsequent flooding. This integrates Basic Science with Civic Education and Community Service.
Sustainable Agricultural Practices: For students from farming backgrounds or those interested in agriculture, the knowledge of erosion control methods (e.g., contour ploughing, mulching, crop rotation, intercropping) can be directly applied to improve farm productivity and soil health. This promotes sustainable farming techniques that are crucial for Nigeria's food security and rural economic development, integrating with Agricultural Science. Informed Urban Planning and Disaster Preparedness: The understanding of drainage patterns, causes of flooding, and prevention methods can empower students to critically assess urban development in their localities. They can become informed advocates for proper urban planning, effective waste management, and the development of robust drainage infrastructure in their cities and towns (e.g., urging local authorities to clear canals before the rainy season). This connects with Geography, Urban Studies, and Governance. ---