ESSO - Indian National Centre for Ocean Information Services

Storm Surge

What is Storm Surge?

Storm surge is the abnormal rise in sea level generated by a hurricane or other intense storm, over and above the predicted or normal astronomical tide. It is caused mainly by atmospheric weather systems such as tropical cyclones, hurricane winds shoving the ocean water up over the coast, although low pressure in the eye also contributes a much smaller amount.

The height of water level rise due to storm surge is the difference at the coast between the observed level of the sea surface and the level that would have occurred in the absence of the tropical cyclone.

What is the interaction of astronomical tide with storm surge?

In general one may expect that if there is a storm surge of x metres and tidal wave of y metres then during high tide total surges would be x+y and during low tide x-y. But, it is found that there is an interaction of storm surge with astronomical tide, and during high tide time the total surge is little less than x+y and during low tide time it is little more than x-y.

What are the disaster potential of Storm Surge?

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)

What are the factors influencing storm surge?

The level of storm surge during a storm is influenced by:

• Size and extent of storm's wind field (radius of maximum winds)
• Strength of storm winds and Storm's forward speed
• Storm track
• Storm's central pressure (contribution of pressure to total storm surge is small compared to wind)
• Landfall location
• Coastal elevation
• Shape and characteristics of the coast

What is the vulnerability of our coastline from the point of view of storm surge potential?

Entire Indian coast can be categorized into 4 zones

• Very high risk zones (Surge height > 5m)
• High risk Zone (Surge height between 3-5m)
• Moderate risk zone (Surge height between 1.5 to 3m)
• The coastal areas and off-shore islands of Bengal and adjoining Bangladesh are the most storm-surge prone (~ 10-13m) - VHRZ
• East coast of India between Paradip and Balasore in Orissa (~ 5-7m) - VHRZ
• Andhra coast between Bapatla and Kakinada holding estuaries of two major rivers Krishna and Godavari (~ 5-7m) - VHRZ
• Tamilnadu coast between Pamban and Nagapattinam (~ 3-5m) - HRZ
• Gujarat along the west coast of India (~ 2-3m) - MRZ

What should I do?

You need to plan well ahead of time. If you live or work in the coastal area, find out from your local Emergency Services or local council whether you are in a surge-prone area. If you are, decide where you will go in the event of a storm surge. You might have a friend living on higher ground with whom you could go and stay. Wherever your nearest safe high ground shelter might be, work out the safest way to get there.

Storm surge prediction model: ADCIRC

ADCIRC is a (parallel) ADvanced CIRCulation model for oceanic, coastal and estuarine waters developed by Dr. R.A. Luettich, Jr, University of North Carolina at Chapel hill, Institute of Marine Sciences (email: rick_luettich@unc.edu) and Dr. J.J. Westerink, Department of Civil Engineering and Geological Sciences, University OF Notre Dame (email: jjw@photius.ce.nd.edu).

The complete information of ADCIRC model can be seen from the below link
http://www.unc.edu/ims/adcirc/document/Introduction.html