Unit F4 - Disaster Planning



Unit F4


The natural world is subject to occasional rare extreme events which can cause great damage both to the natural environment and to people and all that they construct. In rural areas, these natural disasters are most often caused by the following events.

Cyclones or cyclonic storms, also known as hurricanes in the Caribbean or typhoons in the North Pacific, may have high winds sometimes exceeding 200 kilometres per hour and heavy rains often accompanied by very high tides and large waves in coastal areas.

Floods and droughts produced by unusually heavy rainfall or the complete lack of rainfall. Even towns in the Pacific not noted for heavy rainfall have registered amounts up to 270 millimetres of rain in 8 hours, and a metre of rain in 4 days. Heavy rains can also lead to other kinds of disasters such as landslides and dam failures. There are also rural areas where it may not rain for months or the rains may fail entirely. Droughts not only leave people without water and animals without fodder, and cause crops to fail, but unusually dry forests may be swept by disastrous forest fires.

Earthquakes are possible in many parts of the world where the Earth's crust is geologically active. The sudden release of pressures where continental plates push against or slide under each other sends a shock to the surface that can make buildings collapse and cause big changes. An earthquake in Vanuatu in the Pacific lifted parts of some islands about 6 metres out of the water.

Tsunamis, sometimes mis-named "tidal waves", are giant waves caused by earthquakes or underwater landslides that can sweep up on exposed shorelines. If they cross the ocean from a faraway earthquake there may be some warning of their coming, but not if they are generated nearby.

Volcanic eruptions are always a danger in parts of the world where volcanoes are still active. Rocks and ash may be shot into the sky to fall to the ground over large areas, hot lava may pour from the volcano covering everything in its path, and certain types of volcanoes can even explode.

Most of these natural disasters are sufficiently rare that people forget about them. Something that only happens every 50, 100 or 200 years or more on the average does not seem like an immediate danger. However, sooner or later they do happen somewhere. Since most of them occur without any warning, there is no chance to prepare for them at the last minute. Therefore, for most governments, disaster preparedness means planning what you will do once the disaster has occurred.

While extreme natural events cannot be prevented, there is much that can be done to keep them from becoming human disasters. Disaster planning in this sense means taking reasonable precautions based on an understanding of the environment to reduce the vulnerability of people and property to such disasters as may occur. Just as preventive medicine means increasing a person's resistance to disease and reducing their chances of getting sick, so preventive disaster planning means increasing the resistance of the human habitat to natural forces and reducing the risk of damage.

Construction standards

Much can be done to improve construction standards for houses and buildings so that they are less apt to collapse or blow away during a natural disaster. If earthquakes are a danger, concrete and masonry buildings need to be properly reinforced. Wooden buildings with adequate cross-bracing will suffer less damage in an earthquake. In cyclone areas, buildings must be strong enough to resist the force of the wind, and roofs must be correctly tied down internally or externally to the building structure and foundations. It is often the air pressure inside a building that lifts the roof off in a cyclone. In flood prone areas, construction should not be allowed in low-lying areas and building levels should be raised above known flood levels.

A structure does not have to be modern to be resistant to disasters. Many traditional types of construction also provide good protection, particularly where structural members are tied together to provide some flexibility and to resist forces in all directions. However, even small changes in traditional techniques may make a big difference in building resistance. A poorly nailed joint may pull apart more easily than one tied with traditional rope, and wood salvaged from a packing case may not be as strong as the forest poles it replaces.

If there is not enough information available locally on correct building standards, it should not be too difficult to obtain this from countries with more experience. It may be necessary to provide for the inspection of homes and buildings to ensure that the occupants are not at risk, and to make recommendations to strengthen substandard structures.

Flood control

It is not too difficult to calculate from historical rainfall records what could be the heaviest rainfall to be expected in an area or community. From that figure and the area and shape of each watershed, it is possible to determine what volume of water will need to be drained off the area, and where it may collect. This information can be used to plan the size of drains needed for storm runoff in order to avoid flooding.

Often it is not possible or economically feasible to build drainage works big enough for the rare very heavy rains, but it is usually possible to plan for certain low-lying areas where the water can collect without great danger to lives or property. Such areas could be made into parks, playgrounds, gardens or other open spaces where temporary flooding will not do great damage.

Avoiding vulnerable areas

A careful study of the local environment can help to identify those areas that would be the most vulnerable to damage in the event of a natural disaster. The information can come from several sources. Descriptions of the damage caused in previous disasters can often indicate flood levels, wave heights, and wind directions in the case of cyclones, or unstable soils on which buildings move more in earthquakes. There may also be signs in the environment itself, such as ridges of rubble thrown up on the shore, or channels cut through islands by storm waves. Many bent coconut palms, or broken or fallen trees can suggest the extent and even the direction of wind damage. Previous volcanic eruptions may leave scars or deposits from heavy ash falls or lava flows. Calculations using maps or based on the topography of the land and the position of protective features such as reefs or ridges could also show which areas are most exposed or most liable to flooding.

Development should be restricted in areas identified as particularly vulnerable. Housing should not be permitted in such areas if there is a risk of loss of life. Building standards should be adapted to the nature of the risk, such as better resistance to wind in areas known to be affected by cyclone winds, or construction on stilts in low-lying areas subject to flooding.

Natural environmental defences

There are many things in the natural environment that provide defences against the effects of extreme conditions. A healthy coral reef is a natural breakwater that helps to protect the shore against storm waves and tsunamis. The natural shoreline usually has rocks or beaches that also absorb the energy of breaking waves. Coasts subject to heavy storm waves often have a raised ridge or rampart of sand and rubble that shelters the land behind which is usually occupied by houses and gardens.

Plants are also an important protection against wind damage and erosion by waves and flood waters. The important strip of trees and shrubs along the shore both break the force of the wind and help to hold the soil with their roots. Mangrove forests also provide valuable coastal protection. The plants along river and stream banks slow the flow of the water and help hold the banks against erosion. Swamps and flood plains also trap flood waters and allow them to drain off more slowly. The forest or even a row of trees can protect crops and buildings against the full force of the wind. Forests and other vegetation can slow water runoff and reduce flooding, and on slopes they stabilize the soil to hold back landslides.

It is essential to preserve the protective value of these defences as much as possible. Too often passes are blasted in the reef, mangroves are filled in, beaches are mined of their sand, protective rubble ramparts are leveled to make lots with a sea view, coastal and stream bank vegetation is cleared, and trees are cut without thinking about the consequences in the event of a cyclone, tsunami or flood. People are then surprised when areas are affected that had never been damaged previously.

Where natural defences have already been removed, it may be possible to restore them. Mangroves, coastal and stream bank vegetation can be replanted. Gaps in coastal ridges can be filled in. Rows of trees can be planted as windbreaks to protect fields and crops.

There is nothing new about improving defences against disasters; traditional cultures had many protective practices. On one island in Tonga in the Pacific, rows of trees were planted long ago crossing the island in different directions so that at least some of the crops would survive in the event of a cyclone.

With careful environmental planning and a bit of common sense, extreme natural events like cyclones, floods and earthquakes need not become human disasters.


What are some of the natural disasters that have occurred in your country?

Were they made worse because of changes people made in the environment?

Do you think your home is a safe place to be when a cyclone or earthquake happens?

What can be done to make houses and buildings more resistant to the effects of such disasters?

Can you think of places in your area where people should not build houses?

Why are these places dangerous?

Are there signs in your country of previous natural disasters?

What can be done to make your rural area a safer place to live?

Instructions for trainers in the use of this unit


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Last updated 21 June 2008