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S. K. Dube & Tad Murty Indian Institute of technology Kharagpur

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Highlight the current activity in surge modelling and related area in the Bay of Bengal Describe the development of location specific real time stand alone prediction system for providing effective and timely surge forecasts

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Effect of local Tides Effect of local Coastal Configuration Low Atmospheric Pressure in the Centre Wind Rain Storm Surge Storm SurgeFlooding Loss of Human Life: Injuries Loss of Human Life: Injuries Damage to structures & Continent Damage to structures & Continent Flooding of Low- Lying Coastal Areas Flooding of Low- Lying Coastal Areas Erosion of Beaches Damage to onshore & offshore installations Damage to Shipping & Fishing Facilities Loss of Communications & Power Urban Bushfire Loss of Soil Fertility from Saline Intrusion Land Subsidence Contaminati on of Domestic Water Supply Destruction of Vegetation, Crops, Livestock Potential Impact upon Landfall of a Tropical Cyclone

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A Storm Surge is an abnormal rise of sea level caused by a cyclone moving over a continental shelf

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Storm Surge

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DEATHS IN TROPICAL CYCLONES YEAR COUNTRIES DEATHS 1970Bangladesh300,000 1737India300,000 1886China300,000 1923Japan250,000 1876Bangladesh200,000 1897Bangladesh175,000 1991Bangladesh140,000 1833India 50,000 1864India 50,000 1822Bangladesh 40,000 1780Antilles(West Indies) 22,000 1965Bangladesh 19,279 1999India 15,000 1963Bangladesh 11,520 1961Bangladesh 11,466 1985Bangladesh 11,069 1971India 10,000 1977India 10,000 1966Cuba 7,196 1900USA 6,000 1960Bangladesh 5,149 1960Japan 5,000 1972India 5,000

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Review of storm surges in the Bay of Bengal Ali (1979) Rao (1982) Roy (1984) Murty (1984) Murty et al. (1986) Das (1994) Dube et al. (1997, 1999, 2000, 2001) Chittibabu (1999)

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Real Ocean Real Ocean Model Mathematical Model Results Idealization & Approximation Based on experience & understanding of the problem Abstract symbolic Representation Based on Mathematical Experience Solution based on Mathematical Experience COMPARISONCOMPARISON

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Location Specific Input Meteorological Input Oceanographic & Hydrological Input Dynamic Storm Model Wind Stress Associated with Cyclones Storm Surge Model Equations Vertically Integrated Mass Continuity (1) Vertically Integrated Momentum (2) Numerical Solution Results Sea Surface Elevations Extent of Coastal Inundation

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Meteorological Input p Vector motion of the storm Place of landfall Duration of the storm V MAX R MAX

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Oceanographic Data Bathymetry Astronomical tides Inshore currents in closed regions Hydrological Input River discharge in the sea Rainfall distribution

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Location Specific Inputs Coastal representation Convergence of the Bay Effect of coastal geometry on the location of the peak surge

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(Jelesnianski & Taylor, 1973) Model computations are based on balance of force given by (Myers and Malkin, 1961) r = distance from the storm centre p( r ) = the pressure ( r ) = Cross –isobaric angle V( r ) = the wind speed K s = emperical determined wind friction coefficient in the tangential direction K n = emperical determined wind friction coefficient in the radial direction

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R : Radius of the maximum wind V R : Maximum wind speed

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New prognastic variables

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j=1 j=2 j=3 j=4 j=5 j=6 i=1i=2i=3i=4i=5i=6i=7i=8i=9 uv Finite Difference Grid

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STABILITY In this scheme the computational stability is ensured by just restricting the time decrement t governed by CFL criterion (2 gh max ) 1/2 t/ x < 1 Taking into account the maximum depth of water h max encountered within the model, a permissible value of t may be determined

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Location Specific Input Shelf Bathymetry Coastal & River Geometry Meteorological Input Pressure drop of cyclone Radius of Maximum Winds Forecasted Locations of Cyclone Place of Landfall Astronomical Tides Hydrological Input River Water Discharge Dynamic Storm Model Wind Stress Associated with Cyclones Storm Surge Model Equations Vertically Integrated Mass Continuity (1) Vertically Integrated Momentum (2) Integration in Time Results Sea Surface Elevations Extent of Coastal Inundation

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IIT Storm Surge Model Operating Procedure Setup forecast domain by executing an appropriate window Provide an arbitrary number of stations around the forecasted place of landfall of the cyclone for peak surge display Provide duration of forecast Provide tropical cyclone characteristics (preferable six hourly observations) Cyclone positions (lat – long) Pressure Drop (Hp a ) Radii of Maximum Winds (m) Run storm Model & Surge Model

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Ability to investigate multiple forecast scenario in real time Updates cyclone track as the cyclonic storm approaches the coast and meteorological forecast become more accurate

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Surge Envelope Scenario I: Actual Landfall Distance along East Coast of India (km)

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Surge Envelope Scenario II: Landfall at Puri Distance along East Coast of India (km)

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Surge Envelope Scenario III: Landfall at Balasore Distance along East Coast of India (km)

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Andhra Pradesh

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Track of 1990 Andhra Cyclone

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Surge Envelope Scenario I: Actual Landfall Distance along East Coast of India (km) § Place of Landfall

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Surge Envelope Scenario II: Landfall (100 km to left) Distance along East Coast of India (km)

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Surge Envelope Scenario III: Landfall (100 km to right) Distance along East Coast of India (km)

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Track of 1977 Andhra Cyclone

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Peak Surge Envelope Distance along East Coast of India (km)

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BangladeshBangladesh

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BangladeshBangladesh

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Track of 1970 Bangladesh Cyclone

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Surge along Bangladesh Coast

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Track of 1982 GWA Cyclone

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Myanmar

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Peak Surge Envelope 1982 Cyclone

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Track of 1964 Sri Lanka Cyclone

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A real time storm surge prediction systems is proposed for India, Bangladesh, Myanmar & Sri Lanka, which can be run in a few minutes on a PC Only meteorological inputs required for the model are positions of the cyclone, pressure drop and radii of maximum winds at any fixed interval of times

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The system is operated via a terminal menu and the output consists of the 2 D and 3 D views of peak sea surface elevations with the facility of zooming the region of interest The system can handle multiple forecast scenarios The model has extensively been tested with severe cyclonic storms of the last three decades, which have affected the coastal regions in the Bay of Bengal

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Rs. 6,170 Crores of damage and 9,885 deaths are reported to have occurred in the October 1999 Super Cyclone. Can this, and other similar events, be avoided in the future? If so, how and at what cost? January 2002

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The Damage from Cyclones About 90% of the damage is due to inundation of land by sea water and also flooding of the river deltas from the combined effects of tides and surges from the sea penetrating into the rivers, while at the same time excess water in the rivers due to heavy rains from the cyclone is trying to flow through the rivers into the sea The balance 10% of the damage is from the very strong winds from the moving cyclones

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Some Future Directions Use extremely sophisticated state of the art computer models to calculate maximum possible storm surge and maximum possible total water level envelope (MPTWLE) for the Indian coast, under a variety of scenarios

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Earth dykes Sea walls (concrete) Mangrove forests Break waters Storm surge buffer zones (vegetation, reed grass) Sand dunes Through very detailed soil surveys, one can determine for each segment of the Indian coastline which of the following protection measure is most appropriate

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Mitigation of the Damage From the Overflow & Flooding From Rivers Storm surge barriers to prevent the surge from the ocean to penetrate into the rivers A system of dry canals for each river and estuary. During a flooding event, excess water can be diverted into these canals

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Global Storm Surges: Theory, Observations and Applications G. G ö nnert, S. K. Dube, Tad Murty and W. Siefert CONTENTS Introduction and General Considerations The Basic Storm Surge Equations and Standard Methods of Solutions Finite Element Models Special Hydrodynamic Problems Meteorological Aspects Storm Surges Generated by Tropical Cyclones - Case Studies Storm Surges generated by Extratropical Cyclones - Case Studies Impact of Climate Change and Sea level Rise on Storm Surges Die Küste Germany, 2001

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