How to prepare mitigation strategies for specific disasters ?


i) Causes

Normally floods are caused by high rainfall or more snow melt on the higher altitude of mountains. This raises the level of rivers than its normal level leading to floods. Deforestation of the catchment areas and sedimentation in the riverbeds due to soil erosion can increase the severity of adverse effects.

ii) Flood Severity

Severity can be evaluated from following parameters.

(a) Depth of water (flooding),

(b) Area inundated (flooded),

(c) Speed of water flow,

(d) Duration of inundation,

(e) Amount of sedimentation or mud deposition in agricultural field.

iii) Hazard Assessment and Mapping

In case of flood, historical records can provide a rough idea of hazard vulnerability. In case of river floods, topographic mapping and contouring near and around river systems can also be prepared.

iv) Elements of Risk

(a) Everything in the flood plains,

(b) Buildings, particularly "kucha" or earth buildings or masonry with mud or water soluble material,

(c) Building with weak and shallow foundations,

(d) Basements and underground buildings,

(e) Underground electrical and telephone lines,

(f) Water supply (underground pipes),

(g) Sewerage,

(h) Crops, fisheries and hatcheries,

(i) Food stock and other essential supplies,

(j) People and livestock,

(k) Fishermen's boats and nets etc.

v) Mitigation

(a) Land use planning and control to avoid use of flood plains for residential or commercial purposes,

(b) Structural measures like engineering of structures to withstand flood forces and design for elevated floor levels and construction over stilts. Construction of reservoirs, dams, dykes, retaining walls, embankments, constructing alternate drainage courses are structural methods for flood disaster mitigation,

(c) Non-Structural Measures, such as, people's participation through education and creating awareness, sedimentation clearance from rivers, afforestation, effective warning systems, flood resistant houses {with strong foundation and by use of water resistant material), changing farming practices, storage and sleeping area to be much above the ground, flood evacuation preparedness, arrangement of boats and rescue equipment, adoption of afforestation and checking deforestation in the area.

(B) Earthquake

i) Causes

Earthquakes are caused by vibrational energy released by geological adjustments deep in the earth. These may also result from tectonic drift or local geomorphology shifts or volcanic activity.

The vibrations of earthquake cause damage and collapse of structures, which in turn may kill and injure people living in the area. Earthquakes have multiple effects. It can cause landslides, rock-falls and dam failure leading to floods and can cause enormous loss to the settlements in the vicinity. There could also be flooding and fires in urban areas due to broken water mains, gas leak or electric short-circuiting.

ii) Severity

The earthquake severity is reckoned by the magnitude on the Richter Scale, which indicates the amount of energy released at the focus. Higher the magnitude, more is the damage and larger is the area affected.

iii) Hazard Assessment and Mapping

A hazard assessment map of the country/state can be prepared after identification of seismic fault systems and seismic source regions. India has been divided into five seismic zones from the point of vulnerability for earthquakes.

iv) Elements at Risk

In high seismic zones following elements are at risk:

(a) Weak foundation buildings,

(b) Multi-storied buildings,

(c) Buildings constructed by earth (mud), rubble, stone and unreinforced masonry,

(d) Old structures,

(e) Building weakened by subsequent modifications,

(i) Tall building on alluvial soil or slopes,

(g) Underground pipes, power lines, sewerage lines, water supply pipes, telephone wires, etc., and

(h) Industries, chemical, nuclear plants.

v) Mitigation

(a) To follow building codes,

(b) Enforcement of compliance with building codes requirements and, encouragement of higher standards of construction quality,

(c) More emphasis should be given to engineering of structures to withstand vibration forces. High standard of engineering design of all public buildings (hotels, schools and hospitals).

(d) Reduce urban densities in high seismic zones,

(e) Strengthening of existing buildings, monuments strengthening in the vulnerable areas,

(f) Encouraging insurance,

(g) Community participation in constructing safe houses; creating awareness of what to do and what not to do at the time of earthquake. Community action, groups in fire fighting first aid and rescue operation. Regular earthquake drills in the area.

(C) Drought

A major difference between drought and other type of disasters is that droughts do not have a sudden onset such as in case of floods or earthquakes.

i) Causes

Scarcity of rainfall in the area, over exploitation of underground water can aggravate or even cause drought.

ii) Severity

Drought severity depends on:

(a) Rainfall deficiency

(b) Duration of drought

(c) Extent of soil moisture loss and ultimately loss of soil cover

(d) Area affected

iii) Hazard Assessment and Mapping

The meteorological department prepares rainfall map of each state/region. This indicates the normal rainfall pattern of the region. Less than normal rainfall for prolonged period causes drought conditions. Topographic maps can be prepared of the area having more frequent droughts.

iv) Elements at Risk

(a) All types of vegetation and crops,

(b) Human and animal health,

(c) Entire human settlement (in prolonged drought and famine),

(d) All industries, business and other economic activities depending on water, and

(e) Soil system.

v) Mitigation

Both structural and n on-structural mitigation strategies are necessary.

(a) Construction of dams and check dams,

(b) Provision of irrigation facilities,

(c) Watershed management

(d) Food, fodder and water management including rationing, if necessary,

(e) Herd-management

(f) Proper selection of crop for drought affected areas,

(g) Leveling, and soil conservation techniques,

(h) Reducing deforestation and fire wood cutting in the affected areas,

(i) Checking of migration and providing alternate employment for people,

(j) Education and training to the people,

(k) Community participation in construction of check dams, reservoirs, wells, tanks, afforestation, introducing water conservation and efficient water management through community programme, (pani-panchyat in Maharashtra) changing livestock management practices, encouraging self-employment by cottage or village (non-agricultural) industries.

(l) Public Health Management,

Some of the community based programmes like "Sukhomajri" experiment in Haryana or "Ralegaon Sidhi" in district Ahmednagar of Maharashtra should be replicated. These are good examples of water conservation in these areas with the help of local people.

(D) Cyclones

i) Causes

Cyclones generate over sea areas in certain parts of tropics such as the Bay of Bengal and the Arabian Sea and move towards coasts. Intense atmospheric processes cause these in the months of April-May and October/November. These are hundreds of kilometers in diameter and are accompanied by torrential rain and very strong winds.

ii) Severity

Cyclone severity depends upon wind speed and rainfall.

iii) Hazard Assessment and Mapping

Climate charts are available from the India Meteorological Department indicating all the past occurrences of cyclonic storm during the past 150 years. The Department also provides forecasts and warnings for cyclones through a state-of-the-art system.

iv) Elements of Risk

All vulnerable coastal areas:

(a) Weak houses and light-weight structures,

(b) Timber houses,

(c) Loose and poorly attached building elements {Sheets, Boards, etc.),

(d) Telegraph and electrical poles,

(e) Sign boards, fences, trees, etc.,

(f) Fishing boats,

(g) Maritime industries.

v) Mitigation

(a) Engineering structures to withstand cyclonic wind forces,

(b) Suitable building codes for the area having wind load requirement,

(c) Better architectural design of buildings, taking winds speed and wind direction into account,

(d) Planting wind breaker trees in upwind of towns and on coasts,

(e) Cyclone shelters for the community,

(f) Community participation in construction of wind-resistant or easily rebuilt houses. Proper fixing of elements (like metal sheets, rods, angle iron, etc.) that could blow away and cause damage elsewhere. Construction of strong wind resistant shelters for community. Protection to animals, and protection to fishing boats. Cyclone rehearsals (drills) in the vulnerable areas. Selection of means of communication at the time of cyclone (e.g., Ham Radio).