India has a long coastline of 8,000 km, which is exposed to tropical cyclones originating from Bay of Bengal and Arabian Sea .On an average, about five to six tropical cyclones form in the Bay of Bengal and Arabian Sea every year, out of which two to three may be severe. The east coastline of the country is more prone than the west as about 80 percent of the total cyclones generated in the region hit here. There are two definite seasons of tropical cyclones in the North Indian Ocean.
Damages:
When the storm surges, the elements falling in the way of wind pressure/suction, are affected in many ways like windows or window frames which are improperly attached are badly damaged; roof/intel projections get damaged; trees are uprooted and transportation disrupted; many cantilever structures such as signposts, electric poles and transmission line towers fail; improperly attached or constructed parapets fail; roofing elements and walls along the gable ends particularly due to high internal pressure fail and the corrugated iron roofing sheets attached to steel trusses are punched and blown.
Exposure/Vulnerability:
ADVERTISEMENTS:
The human settlement vulnerability is ascertained by its location, degree to which its structure and buildings can be damaged and the probability that a cyclone will occur. The buildings which are not able to with-stand the fury of high speed and surging storm are considered vulnerable.
The lightweight structures with wooden frames and older buildings where wood has deteriorated and weakened the walls are generally the ones which are most vulnerable to cyclones. Also vulnerable are the houses which are made of poorly constructed concrete blocks. People living on river flood plains, low-islands and on unprotected low lying coastal areas are prone to cyclones. There are certain settlement patterns those may create an effect that increases the velocity of wind between buildings and create even greater damage.
Safety Measures:
The site selection is a very important feature of safety measures. Therefore utmost care should be taken for site selection. In non-cyclonic region the predominant strong wind is well established. Hence the area behind a mound or a hillock should be preferred to provide for natural shield. Similarly, thick plantation upwind will act as a shield. On the other hand the construction along ridges in hilly regions should not be undertaken as they face an accentuation of wind velocity. However, the valleys experience lower speeds in general.
ADVERTISEMENTS:
The storm tides that lead to coastal inundation are commonly generated by cyclonic windstorms. While choosing a site in the cyclonic region, close to the coast, due consideration should be given to the site which is above the inundation level. In case the high elevation natural ground is not available then in that case construction should be done on stilts with no masonry or mounds to avoid flooding/inundation.