CBSE Class 8 Social Science Disaster Management Notes

CBSE Class 8 Social Science Disaster Management Notes. Learning the important concepts is very important for every student to get better marks in examinations. The concepts should be clear which will help in faster learning. The attached concepts made as per NCERT and CBSE pattern will help the student to understand the chapter and score better marks in the examinations.

DISASTER MANAGEMENT

MINERAL

• Earthquake : An earthquake is a sudden release of energy accumulated in deformed rocks which causes the ground to tremble or shake.
• Seismograph : It is an instrument which measures and records vibrations of an earthquake.
• Richter Scale : Richter scale is the scale having 0 to 9 range used to measure the magnitude and intensity of an earthquake. One point increase represents 10 times magnitude of the earthquake.
• Landslides : Sliding of mass of rock, earth an debris which move down a slope of a mountain by their own force and weight are termed as landslides.
• Debris flow : Flow of debris in the Western Ghats of kerala down the slopes is called debris flow.
• Floods : Floods are temporary inundation of large areas due to an increase in reservoir or due to rivers flooding their banks because of heavy rains, cyclones etc.
• A Cyclone : A Cyclone is a violent storm, often of vast extent, characterised by high winds rotating about a calm centre of low atmospheric pressure.
• A Drought : A drought is an insidious natural hazard that results from a departure of precipitation over a season or longer period of time, insufficient of meet the demands of human, plant and animal activities.
• Watershed : Watershed is the geographic area where water flows to a common point.

INTRODUCTION

• There are several hazards.
• Each hazard has its own characteristics.
• We have to keep these characteristics in mind while taking steps for their mitigation.
• Causes and effects of hazards help us to select strategies for mitigation of hazards.

Several Types of Hazards :
Several types of hazards have widespread concern to us. For a simple understanding of hazards, we classify them as under

• Sudden on-set Hazards : Earthquakes, tsunamis, volcanic eruptions, landslides, floods, tropical cyclones, avalanche, cloud burst etc.
• Slow on-set Hazards : Drought, famine, environmental, degradation, pest infestation, desertification.
• Epidemics : Water/food borne diseases, person to person diseases, vector borne diseases.
• Industrial technological Accidents : System failures, fire, explosion, chemical leakage/spillage.

Wars and Civil Strifes :
The structure for common hazards and mitigation is described in the following sequence

• On set type.
• Hazard assessment.
• Warning
• Main mitigation strategies.
• Elements at risk.
• Community based mitigation

Typical effects

We should keep the following points in mind while taking steps to mitigate the impact of hazards :

(i) All disasters have different typical effects.
(ii) The mitigation strategies are to be taken up as per the local conditions.
(iii) Looking at multi-hazard zones in terms of possible combined effects. Example:
Heavy rains can cause floods and in certain regions it can even trigger landslides if the ground conditions are conductive to them.
(iv) The impact of the disaster depends on community preparedness, natural constraints, management and institutional mechanism.

EARTHQUAKES

Definition : An earthquake is a sudden release of energy, which has accumulated in deformed rocks, causing the ground/earth to tremble or shake.

Onset Type and Warning :

• Earth quake onsets suddenly.
• They occur at any time, day, night and at any time of the year.
• They occur all of a sudden without any advanced warning.
• Their impact is sudden.
• Earthquakes cannot be predicted despite extensive researches and investigation in recent decades.

Elements at Risk :

The following elements are at risk during earthquakes

1. Settlements :
• Settlements in earthquake prone areas-built on alluvial and wind blown soil deposits.
• Settlements built in landslide prone areas.
• Settlements built along geological fault lines.

2. Buildings :
• Weak and having high occupancy.
• Traditionally built using earth, rubble, bricks by masons.
• Buildings with heavy roofs.
• Buildings with poor quality material.
• Buildings with poor maintenance.
• Buildings with weak and flexible storage.

Typical Effects Of Earthquakes

1. Physical Damage :
• Damage of building
• Damage to service structure
• Fires due to short circuit
• Floods due to dam failures.
• Landslides, in hilly and mountainous regions.

2. Casualties :
• Very high near the epicentre
• Very high in thickly populated areas.
• In buildings. which are not earthquake resistant.

3. Public Health :
• Multiple fracture injuries.
• Moderately and most severaly injured
• Break down in sanitary conditions
• Unhygenic conditions leading to spread of epidemics.

4. Water Supply :
• Failure of water supply/distribution system, water supply network.
• Failure of fire hydrants and non control on fires.

5. Transport Network :
• Breach in roads and railway lines.
• Failure of airport run ways.
• Collapse of related infrastructure.

6. Communication :
• Failure and collapse of transmission towers, transponders
• Disconnection of telephone and telegraph lines.
• Damage to telephone exchange

7. Electricity :
• Failure of transformers
• Breaking of electric wires network

MAJOR MITIGATION STRATEGIES REGARDING EARTHQUAKES

1. Engineered Structures :

• Buildings to be designed and built to withstand ground shaking.
• Architectural and engineering inputs to be put together to improve building design and building practices.
• Intensive analysis of soils before starting construction.
• No construction of buildings on soft soil.
• Building codes and guidelines to be enforced strictly. The Bureau of Indian Standards publisher these codes and guidelines.
• Municipality to check the building plan thoroughly before starting construction, as per building bylaws. Building design should satisfy all building bylaws for safety and comforts.
• Existing big buildings such as hospitals, schools and fire stations should be upgraded by retrofitting techniques.
• Architects, buildings, constructors, designers, engineers, fmanciers, government, functionaries, houseowners and masons should be given training to sensitise them. This will create public awareness.
• Construction of building should be avoided in the areas prone to fires, floods, landslides, earthquakes and cyclones.

LANDSLIDES

Definition
Landslides are sliding masses of rock, earth and debris which move down of slopes or river banks due to their own weight.

• Onset Type and Warning
• Generally onset type of landslides is gradual or slow.
• But due to failure of the mass (sliding of material) along the slopes the landslides occur all of a sudden without any warning.
• Landslides occur during earthquakes, floods and volcanic eruption. Or in other words landslides occur accompanied with earthquakes, floods and volcanic eruptions.
• There is no established warning system about landslides. Hence, no one can predict landslides in advance.
• Study and analysis of geology, hydrology, vegetation cover, past occurrence and consequences of landslides help in getting information about landslides.

Elements at Risk :
Major elements at risk of landslides are given below :

1. Settlements :
• Settlements built on steep slopes.
• Settlements built on the toe of slopes.
• Settlements built on the mouth of streams which come down of mountains into the valley.

2. Buildings :
• Buildings built without adequate foundation for a given soil.
• Buildings constructed on soft soils
• Buildings constructed on slopes or at toes of slopes.

3. Roads

4. Communication lines

5. Buried lines of utilities.

FLOODS

Definition
A flood is a temporary in induction of large area due to increase in the water of reservoir as a result of heavy rains.

Onset Type and warning

• Onset :
• Floods occur both gradually and suddenly. It depends on the amount of water received through rains.
• Floods are caused by heavy rains.
• Tsunamis also cause sudden floods.

TYPICAL EFFECTS OF LANDSLIDES

1. Physical Damage :
• Landslides destroy everything that comes in their way
• They block roads. They bury them
• Communication lines are buried in the debris of lanslides
• Settlements are buried in the debris
• River flow is blocked causing floods overhead
• Agricultural land
• Loss of agricultural production and land areas
• Floods occur, thus doubling the plight of the people

2. Casualties :
• Place and time of occurrence of landslides play an important role in causing the extent of casualties.
• Large nubmer of people die every year :

— Debris slides caused earthquake on the slopes of Huascaran in Peru in 1970.
— It killed 1•, 000 people.

MAJOR MITIGATION STRATEGIES

1. Hazard· Mapping :
• It helps locate areas prone to slope failure (landslides's areas).
• Construction building are avoided in these areas.

2. Land use Practices :
• Existing landuse practices should be preserved such as forested areas and vegetation covers.
• Natural grasslands should be preserved and protected.
• Naked slopes should be covered with vegetation.
• Natural drainages should be maintained and kept clear of any debris etc.

3. Retaining walls : Should be erected along weak slopes/steep slopes.
• They check level from slipping.

4. Surface Drainage Control :
• Surface drainage control works control the movement of landslides.
• They also put check on infiltration of rainwater and spring flows.

5. Engineered Structures :
• Buildings with strong foundations withstand the movement of debris.
• Underground installations should be made flexible to withstand the forces of movement of debris etc.

6. Vegetation Cover :
• Increasing vegetation cover is the cheapest means of controlling landslides.
• It bend the upper soil layer and does not allow it to be eroded.
• Excessive run off is controlled.

Warning :
• Generally there is a warning about floods except in case of flash floods.
• Heavy rains are the sufficient warning for floods in rivers.
• In India flood warnings are made by Central Water Commission, Irrigation and Flood Control Department, Water Resources Department.
• Flood forecasting made by central water commission is based on 132 forecasting stations which cover most of the interstate flood prone rivers,

— Central water commission also covers inflow forecasts for 25 reservoirs of India.
— It forecasts 6, 000 forecasts annually with about 950% of the forecasts withiin the pennissible limits.

Elements at Risk of Floods :
• Anything lying! situated in the flood plain.
• Building built on weak foundations and water soluble materials.
• Buildings with basements.
• Sewerage, water supply, are always at rik.
• Transport and communication lines.
• Food stock.
• Agricultural lands
• Live stock
• Vehicles.
• Machinery and equipments.
• Salt pans.
• Fishing boats etc.

Typical Effect of Floods

Major typical effects of floods are enumerated as under:

1. Physical Damage :
• Structures damaged by washing waters.
• Landslides triggered due to water saturation.
• Loss/damage of fishing boats and nets.
• Houses/huts in lowlying areas are washed away causing heavy loss to life and property.

2. Casualties and Public Health :
• Drawing causes death to people and Iivestock.
• Numerous injuries.
• Outbreak of epidemics, diarrhoea, viral infection and malaria.

3. Water Supply :
• Pollution of drinking water.
• Contamination of water.
• Scarcity of safe drinking water.

4. Crops and Food Supply :
• Food shortage due to spoilage of food stocks.
• Loss to entire harvest.
• Soil characteristics are adversely affected.
• Infertile agricultural land due to sand deposits.
• Soil erosion.
• Salinity of soil may increase.

MAJOR MITIGATION STRATEGIES

1. Mapping of the Flood Plains :
• It reduces the risk of flooding of the areas mapped.

2. Landuse Control :
• It reduces the risk of life and property being lost in flood plains and coastal areas because land use controls inhabitation in these flood prone areas.
• No developmental work in flood prone areas.
• Major facilities to be avoided from flood prone areas.
• Water holding areas should be created in all urban and rural areas like ponds, lakes an reservoirs.

3. Construction of Engineered Structures
• Avoidance of construction in flood prone areas.
• Strengthening of existing structures.
• Construction on elevated platform.
• Building on stills or raised platform.

4. Flood Control :
Flood Reduction : Decreasing the amount of runoff by
— reforestation
— Protection of vegetation
— Clearing of debris from streams and other water holding areas.
— Construction of ponds and lake

Flood Diversion includes:
— Leaves
— Embanks of rivers
— Construction of dams

Flood Proofing includes :
— Use of sand bags of keep flood water away.
— Blocking or sealing of doors and windows of houses.
— Houses on raised platforms.
— Construction of houses away from water bodies.

CYCLONES

Definition
Cyclones are defined as the violent storms, often of vast extent with high winds rotating around a calm centre of low atmospheric pressure and moving onward with a wind velocity of 50 kms per hour.

Onset Type and Warning :

Onset :
• Cyclones take time to build up.
• They strike suddenly.
• Their movement is tracked by satellite tracking .
• Their build up and likely can be projected.

Warnings :
• Warning is the given along the projected path of the cyclones.
• It is difficult to predict the accuracy of the path.
• Accurate predictions are made only a few hours before they threaten the population.
• Indian meteorological department issue warning against cyclones and other Phenomena.

• Elements at Risk :
The following elements are at risk of cyclones :
• All lightweight structures, (houses, huts) built of mud and wood.
• Old buildings with weak walls.
• Structures without proper anchorage to the foundations.
• Settlements located in low lying coastal areas, are vulnerable to cyclones, strong winds, heavy rains and storm surge.
• Settlements located near coastal areas are vulnerable to floods, mudslides, landslides, debris flows due to floods.
• Fences, telephone and electric poles, cables.
• Light elements of structures such as roofs, signboards, hoardings, fishings boats.
• Falling trees.
• Structures with tin roofs.

Typical Effects of Cyclones

1. Physical Damage :
• Wind force, flooding, storm surge and landslides, mudslides, debris-slides damage structures extensively.
• Lightweight roofed structures are severely damaged.

2. Casualties and Public Health :
• Flooding and flying objects cause heavy toll to life.
• Falling houses, roofs, walls kill countless people.
• Thousands of people are injured, lakhs are rendered homeless.
• Flooding and casualties lead to contamination of water and this in turn, spreads viral diseases, diarrhoea and malaria.

3. Water Supplies
• Floods water contaminate ground and piped water.
• Water carrying pipelines are damaged, resulting in the disruption of water supply.

4. Agricultural Crops and Food Supplies :
• High winds, heavy and flooding destroy standing crops.
• Food stocks in low lying areas are damaged beyond use.
• Banana and coconut crops are extremely vulnerable to cyclones.
• Sea water increases soil salinity and render it unfit for cropping and cultivation.

5. Transport and Communication:
• Roads and railway lines are damaged.
• Communication are disrupted severely.
• The affected areas remain cut off for days together from the rest of the country/world.

Major Mitigation Strategies for Cyclones :

1. Hazard Mapping
• Map of the area indicates vulnerable points/spots.
• Core is taken to save these spots during cyclones.
• Mapping is the most effective mitigation tool.

2. Land use Control
• Land use indicates that vulnerable areas should not have any rievelopmental activities.
• No construction to be carried out in low lying areas.
• Shelter belts to be created in the cyclone prone areas.
• No settlements in flood plains and near the coasts.
• Vulnerable areas should be used in parks, playgrounds and grazing fields.
• Houses foundation to be strong with cement concrete and horizontal beams.

3. Multi-purpose Cyclone Shelters :
• Multi-purpose cyclone shelters should be built in coastal areas.
• Such shelters have come up in coastal Orissa after the super cyclone of Oct. 29, 1999.

4. Engineered Structures :
• Buildings to be built to withstand strong winds, cyclones.
• Site selection to be made with atmost caution.
• In coastal areas buildings should not be constructed with local material.

Good material should be used :
— Buildings on stilts and raised platforms.
— Wind and water resistant buildings.
— Houses to be strengthened to resist wind and flood damages.
• Foundations of houses should be wide, made of cement, concrete and horizontal beams.
• Roofs and other elements of the structures should be properly anchored to avoid uplift or fyling of light weight roofs etc.
• Overhangs and projections should be properly tied down.
• Plantation of rows of trees near the houses will restrict the high winds and check major damage to the houses.

5. Flood Management
Measures should be taken to manage floods. The following measures will help in managing floods to a great extent.
(i) reforestation,
(ii) protection of vegetation,
(iii) clearing of debris from streams and other water holding areas,
(iv) conservation of ponds and lakes etc.

Flood Diversion includes, embankments, dams and channel improvement.
(i) Dams store water and release water at a manageable rate.
(ii) Flood Proofing reduces the risk of damage.

Measures to divert floods include
(a) Use of sand bags to keep flood water away.
(b) Blocking and sealing of doors and windows of houses etc.
(c) Houses are elevated by raising them through structural means or by raising the land
(d) Buildings are to be constructed away from water bodies.

6. Coastal Shelter Belts Plantation Programme :
Flood shelters like this are just one example of how communities can protect themselves from the the worst floods. Banks of earth are raised by upto 15 feet and cover and area of several kilometres. The people dig a huge pond in the middle and use this earth to raise the ground. Whenever the floods come, people can bring their livestock. Possessions-even their homes-to safety. The pond in the middle becomes an important source of food, as it is used to farm fish.

CASE STUDY OF 1999 ORISSA CYCLONES 1999 SUPER CYCLONE OF ORISSA

• The severe cyclones· on the Northern orissa coast on the night of 29-30 October, 1971 caused nearly 10,000 deaths and extensive damage to crops and property.
• The energy released from the tropical cyclone with high velocity was considered equal to the energy released by the explosion of 200 hydrogen bombs.
• Branches and leaves of the trees turned dark brown.or black.
• Sea waves rose upto 10 metres in coastal areas.
• In inundated several thousand square kilometres of agricultural lands:
• The cyclone 29 October 1999, hit the Orissa coast. It originated in the middle of the Bay of Bengal on 25 October.
• Sea water up to 1.5 metres deep, inundated the coast as far as 15 km inland from the port of Paradwip.
• The tidal waves rose up to 4-5 metres high.
• The cyclorle uprooted trees, knocked down utility poles and flooded large part of the coast.
• It killed 30,000 people and affected crores of families and children.
• It was a super cyclone.

DROUGHT

Definition
A drought is an insidious natural hazard that results from a departure of precipitation from over a season or longer period of time, insufficient to meet the demands of human, plant and animal activities.

Onset Type and Warning :
• Drought is a slow-onset disaster.
• It is difficulf to record the time of its onset and its end.

Drought Warning :
• Falling rainfa!l levels, falling groundwater levels, drying wells, rivers and reservoirs and poor agricultural production warn us the onset of drought.
• A country is drought affected when the overall rainfall deficiency is more than 10 per cent of the long
period average and more than 20 per cent of the country's areas is affected by drought conditions,
according to the Indian Meteorological Department.

Elements at Risk of a Drought :
• Rainfed crops and then irrigated crops.
• Areas with minimum alternative water sources to rainfall.
• Areas subjected to drastic environmental degradation.
• Areas in which livelihood alternative to agriculture are least developed.
• Herdsman, landless labourers, subsistence farmers, women children and farm animals.

Different Typical Effects of Droughts :
1. Droughts do not cause any structural damages.
2. Their typical effects are :
(a) loss of crop, dairy, timber (forest fires), and fishery production;
(b) increase in energy demand for pumping water;
(c) reduced energy production;
(d) increased unemployment;
(e) loss of biodiversity;
(f) reduced water, air and landscape quality;
(g) groundwater depletion;
(h) food shortage;
(i) health reduction loss of life increased poverty;
(j) reduced quality of life; and
(k) social unrest leading migration.

Importance of Watersheds in the Water Supply Augmentation and Conservation
Watersheds : For water supply augmentation and conservation.
Watershed is the geographic area where water flows to a common point. In order to mitigate the drought impact, all kinds of sail and water conservation measures are taken up. In this work local communities are involved. The approach helps these areas to manage efficiently the soil, vegetation, water and other resources. By conserving scarce water sources and improving the management of soil and vegetation, watersheds create conditions conducive to higher agricultural productivity. They also conserve natural resources.

Major Mitigation Strategies for Drought :
1. Drought monitoring : It is a continuous observation of rainfall situation, water availability in reservoirs, lakes,rivers and comparing with the existing water needs of various sectors of the society.
2. Water supply augmentation and conservation : This is done through rainwater harvesting in houses and farmers fields. It increases the content of water available. Water harvesting by either allowing the runoff water from all the field to a common point or allowing it to infiltrate into the soil where it has fallen helps increase water availability for sustained agricultural production.
3. Expansion of irrigation facilities : This reduces the drought vulnerability.
4. Land use : based on its capability helps in optimum use of land and water. It avoids the undue demand created due to their misuse.
5. Livelihood planning : identifies those livelihood which are least affected by the drought. Some of such livelihoods are :
(a) increased off-farm employment opportunities.
(b) collection of non-timber forest produce from the community forests.
(c) raising goats, and
(d) carpentry.

Droughts :
1. It is a temparory condition of water scarcity
2. They are not so frequent in arid and semi arid regions.

Aridity :
1. It is a permanent condition of water scarcity
2. Arid and semi arid regions are prone to droughts.

Drought and. Scarcity :
• Drought and aridity are closely related. Both of them are caused by shortage of water.
• Aridity is a permanent condition.
• Drought is a temporary situation.
• Arid and semi arid regions are prone to drought.

Types of Droughts :
Based on their cause, nature and character, droughts are classified as -
(i) Meteorological (ii) Hydrological (iii) Agricultural and (iv) Ecological.

Meteorological drought is caused when the average annual rainfall is 25 percent less than normal.Hydrological drought comes into existence when the water level in the surface and ground falls.The agricultural drought occurs when the soil moisture goes below the level needed to sustain plant growth.Ecological drought occurs when the productivity of a natural ecosystem fails and causes enviromental damage resulting in the death of a large number of cattle, wild-life or trees in the forests.

Causes of Droughts :
• The main cause of drought is the inadequate and uneven distribution of rainfall :
(i) Rainfall in west and central India is uncertain. It is received in the monsoon season. It is also inadequate.
(ii) The scarcity of rainfall causes hydrological and agricultural drought.
• About 19 percent of the total area ofIndia experiences drought. It effects 12 percent of the tot~1 population of India.
• Drought is regular feature in some states of India. About 30 percent of the country's total area is drought prone. 500 lakh people and 68 present of total sown area are affected annually by droughts. Extreme severe and moderate are three types of drought prone areas.

Impact of Droughts :
• Droughts result in scarcity offoodgrains (akal), water Galkal), fodder (tinkal) and often all of these (trikal).
• The succeeding famine leads to mass migration of humans and livestock.
• During the famines of 1868-69, all the village between Jodhpur and Pali, spread over 65 square kilometres,in Thar Desert were abandoned.
• Between 1812 and 1940, 30 to 80 percent of the livestock population were destroyed.
• In 1987, a severe drought affected thirteen states. Such as Andhra Pradesh, Gujarat, Himachal Pradesh, Karanataka, Kerala, Madhya Pradesh, Maharashtra, Nagaland, Orissa, Punjab, Rajasthan, Tamil Nadu and Uttar Pradesh and two lakh villages, a cropped area of 454 lakh hectares and a population of 2,850 lakh.
• The failure of monsoon in 2002 created drought in most of the Central, Western and Southern States of India.

Reducing Impact of Drought
The following measures will help reduce the impact of drought in the country.
(i) Planning for mitigation of drought be taken up on war footings.
(ii) Various devices of remote sensing, satellite mapping and GIS (Geographical Information System) be used for identifying water aquifers. Integrated wate perverting programmes with active people participation.
(iii) River waters from surplus areas should be transferred to deficit areas. It will solve the problem of drought and scarcity of water throughout the country.

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