Storm Surge During Cyclone


Ajit Kumar AJIT KUMARWISDOM IAS, New Delhi.

Storm Surge is an abnormal rise of sea level as the cyclone crosses the coast. Sea water inundates the coastal strip causing loss of life, large scale destruction to property & crop. Increased salinity in the soil over affected area makes the land unfit for agricultural use for two or three seasons.
Storm surge depends on intensity of the cyclone (Maximum winds and lowest pressure associated with it and Coastal bathymetry (shallower coastline generates surges of greater heights).
Disaster potential
Disaster potential due to cyclones is due to high storm surges occurring at the time of landfall. The storm surges are by far the greatest killers in a cyclone. as sea water inundates low lying areas of the coastal regions causing heavy floods, erosion of beaches and embankments, damage to vegetation and reducing soil fertility. Flooding due to storm surges pollute drinking water sources resulting in shortage of drinking water and causing out-break of epidemics, mostly water borne diseases Very strong winds (Gales) may cause uprooting of trees, damage to dwellings, overhead installations, communication lines etc., resulting in loss of life and property. Past records show that very heavy loss of life due to tropical cyclones have occurred in the coastal areas surrounding the Bay of Bengal. Cyclones are also often accompanied by very intense & heavy precipitation (exceeding 40-50 cm in a day or about 10cm or more per hour in some places)


Vulnerability of Indian  coastline


Entire Indian coast can be categorised into 4 zones



  1. Very high risk zones (Surge height > 5m)


  2. High risk Zone (Surge height between 3-5m)


  3. Moderate risk zone (Surge height between 1.5 to 3m)


  4. Minimal risk zone ( Surge height < 1.5m)


Accordingly



  1. The coastal areas and off-shore islands of Bengal and adjoining Bangladesh are the most storm-surge prone (~ 10-13m) – VHRZ


  2. East coast of India between Paradip and Balasore in Orissa (~ 5-7m) – VHRZ


  3. Andhra coast between Bapatla and Kakinada holding estuaries of two major rivers Krishna and Godavari (~ 5-7m) – VHRZ


  4. Tamilnadu coast between Pamban and Nagapattinam (~ 3-5m) – HRZ


  5. Gujarat along the west coast of India (~ 2-3m) -MRZ



Highest Storm Surge


The Bathurst Bay Hurricane, also known as Tropical Cyclone Mahina, struck Bathurst Bay, Australia in 1899. It produced a 13 m (about 42 ft) surge, but other contemporary accounts place the surge at 14.6 m (almost 48 ft). Considering cyclones over north Indian Ocean, cyclone of 1970 has produced maximum storm surge of 13 metres in recent years. Some of the significant storm surges (metres) over the region are mentioned below.



  1. Hooghly river (WB), October, 1737 : 13


  2. Contai (WB), October, 1864 : 10-13


  3. Bangladesh cyclone, November, 1970 : 13


  4. Paradip, Orissa,October, 1971 : 4-5


  5. Balasore Orissa, May, 1989 : 3-6


  6. Orissa Super Cyclone, October, 1999 : 5-6


 

Saturday, 01st Feb 2014, 07:04:35 PM

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