While it is of course not possible to prevent a tsunami, in certain tsunami prone countries some measures have been taken to reduce the damage caused on shore.
Japan has implemented an extensive programme of building tsunami walls of up to 4.5m (13.5 ft) high in front of populated coastal areas.
Other localities have built flood gates and channels to redirect the water from incoming tsunamis. However, framed structures in the area.
The wall may have succeeded in slowing down and moderating the height of the tsunami but it did not prevent major destruction and loss of life.
Some other systematic measures to protect coastlines against tsunamis include:
Site Planning and Land Management-
Within the broader framework of a comprehensive plan, site planning determines the location, configuration, and density of development on particular sites and is, therefore, an important tool in reducing tsunami risk.
The designation and zoning of tsunami hazard areas for such open-space uses as agriculture, parks and recreation, or natural hazard areas is recommended as the first land use planning strategy.
This strategy is designed to keep development at a minimum in hazard areas.
In areas where it is not feasible to restrict land to open-space uses, other land use planning measures can be used.
These include strategically controlling the type of development and uses allowed in hazard areas, and avoiding high-value and high occupancy uses to the greatest degree possible.
Engineering structures – Most of the habitation of the fishing community is seen in the coastal areas. The houses constructed by them are mainly of light weight materials without any engineering inputs.
Therefore there is an urgent need to educate the community about the good construction practices that they should adopt such as:
Site selection – Avoid building or living in buildings within several hundred feet of the coastline as these areas are more likely to experience damage from tsunamis.
Construct the structure on a higher ground level with respect to mean sea level.
Elevate coastal homes: Most tsunami waves are less than 3 meters in height. Elevating house will help reduce damage to property from most tsunamis.
Construction of water breakers to reduce the velocity of waves.
Use of water and corrosion resistant materials for construction.
Construction of community halls at higher locations, which can act as shelters at the time of a disaster.
Flood management - Flooding will result from a tsunami. Tsunami waves will flood the coastal areas. Flood mitigation measures could be incorporated.
Possible Risk Reduction Measures:
Coastal belt plantation –
Green belt plantation along the coastal line in a scientific interweaving pattern can reduce the effect of the hazard. Providing a cover through green belt sustains less damage.
Forests act as a wide buffer zone against strong winds and flash floods. Without the forest the cyclone travel freely inland.
The lack of protective forest cover allows water to inundate large areas and cause destruction. With the loss of the forest cover each consecutive cyclone can penetrate further inland.
Hazard mapping –
Meteorological records of the wind speed and the directions give the probability of the winds in the region. Cyclones can be predicted several days in advance.
The onset is extensive and often very destructive. Past records and paths can give the pattern of occurrence for particular wind speeds.
A hazard map will illustrate the areas vulnerable to cyclone in any given year. It will be useful to estimate the severity of the cyclone and various damage intensities in the region.
The map is prepared with data inputs of past climatological records, history of wind speed, frequency of flooding etc.
Land use control-
designed so that least critical activities are placed in vulnerable areas. Location of settlements in the flood plains is at utmost risk.
Sitting of key facilities must be marked in the land use. Policies should be in place to regulate land use and building codes should be enforced.
Engineered structures –
structures need to be built to withstand wind forces. Good site selection is also important. Majority of the buildings in coastal areas are built with locally available materials and have no engineering inputs.
Good construction practice should be adopted such as:
Cyclonic wind storms inundate the coastal areas. It is advised to construct on stilts or on earth mound.
Houses can be strengthened to resist wind and flood damage. All elements holding the structures need to be properly anchored to resist the uplift or flying off of the objects.
For example, avoid large overhangs of roofs, and the projections should be tied down.
A row of planted trees will act as a shield. It reduces the energy.
Buildings should be wind and water resistant.
Buildings storing food supplies must be protected against the winds and water.
Protect river embankments. Communication lines should be installed underground.
Provide strong halls for community shelter in vulnerable locations.
Flood management –
Torrential rains, strong wind and storm range leads to flooding in the cyclone affected areas. There are possibilities of landslides too. Flood mitigation measures could be incorporated (see section on floods for additional information).
Improving vegetation cover –
The roots of the plants and trees keep the soil intact and prevent erosion and slow runoff to prevent or lessen flooding. The use of tree planted in rows will act as a windbreak.
Coastal shelterbelt plantations can be developed to break severe wind speeds.
It minimizes devastating effects. The Orissa calamity has also highlighted the need for urgent measures like shelterbelt plantation along cyclone-prone coastal areas.
Species chosen for this purpose should not only be able to withstand the impact of strong cyclonic winds, but also check soil erosion.
Possible Risk Reduction Measures:
Mapping of the flood prone areas is a primary step involved in reducing the risk of the region. Historical records give the indication of the flood inundation areas and the period of occurrence and the extent of the coverage.
Warning can be issued looking into the earlier marked heights of the water levels in case of potential threat.
In the coastal areas the tide levels and the land characteristics will determine the submergence areas. Flood hazard mapping will give the proper indication of water flow during floods.
Land use control will reduce danger of life and property when waters inundate the floodplains and the coastal areas. The number of casualties is related to the population in the area at risk.
In areas where people already have built their settlements, measures should be taken to relocate to better sites so as to reduce vulnerability.
No major development should be permitted in the areas which are subjected to high flooding.
Important facilities like hospitals, schools should be built in safe areas. In urban areas, water holding areas can be created like ponds, lakes or low-lying areas.
E.g: KhashDhalai Flood Shelter.
Flood shelters are just one example of how communities can protect themselves from the worst of the floods.
Banks of earth are raised by up to 5 metres and cover an area of several kilometers. 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.
Construction of engineered structures in the flood plains and strengthening of structures to withstand flood forces and seepage.
The buildings should be constructed on an elevated area. If necessary build on stilts or platform.
Flood Control aims to reduce flood damage. This can be done by decreasing the amount of runoff with the help of reforestation (to increase absorption could be a mitigation strategy in certain areas), protection of vegetation, clearing of debris from streams and other water holding areas, conservation of ponds and lakes etc.
Flood Diversion include levees, embankments, dams and channel improvement. Dams can store water and can release water at a manageable rate.
But failure of dams in earthquakes and operation of releasing the water can cause floods in the lower areas.
Flood Proofing reduces the risk of damage. Measures include use of sand bags to keep flood water away, blocking or sealing of doors and windows of houses etc.
Houses may be elevated by building on raised land. Buildings should be constructed away from water bodies.
In India, systematic planning for flood management commenced with the Five Year Plans, particularly with the launching of National Programme of Flood Management in 1954.
During the last 48 years, different methods of flood protection structural as well as nonstructural have been adopted in different states depending upon the nature of the problem and local conditions.
Structural measures include storage reservoirs, flood embankments, drainage channels, antierosion works, channel improvement works, detention basins etc. and non-structural measures include flood forecasting, flood plain zoning, flood proofing, disaster preparedness etc.
The flood management measures undertaken so far have provided reasonable degree of protection to an area of 15.81 million hectares through out the country.