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139736eo.pdf (20MB) - Japan Oceanographic Data Center

139736eo.pdf (20MB) - Japan Oceanographic Data Center

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STORM SURGES IN THE BAY OF BENGAL*T.S. MURTY', R.A. FLATHER2 AND R.F. HENRY''Institute of Ocean SciencesSidney, B.C., Canada2 Institute of <strong>Oceanographic</strong> SciencesBidston, U.K.INTRODUCTIONCoastal floods associated with storm surges - the changes in water level generated by stormspassing over the sea - surpass even earthquakes for loss of life and property damage (SHAH, 1983).Nowhere are these losses more serious than in the Bay of Bengal (Fig. 1). About 60% of all deathsdue to storm surges have occurred in the low-lying arable coastal areas of the countries bordering theBay and the adjoining Andaman Sea, with Bangladesh alone accounting for about 40% (MURTY,1984). The steady increase of population continuously increases the potential for disaster.The surges are caused by tropical cyclones which develop in the southeast part of the Bay orin the Andaman Sea at certain times of the year. The cyclones move along tracks that frequently crossthe continental shelves bordering the Bay. A storm surge is generated partly by the resulting variationsin atmospheric pressure, but the main contribution is produced directly by the winds, often ofexceptional strength, acting over shallow water.A comprehensive list of all Bay of Bengal surges for which some indication of surge severityis available is given in Table 2. By referring to Figure 1, it can be seen just how much coastline isvulnerable. Thailand is exceptional in that there is no record of its west coast, facing the AndamanSea, having experienced a major surge. Storm surges are much less frequent in Sri Lanka than inBangladesh, India or Burma.While immediate loss of life is often the most dramatic result of a major surge, other effectsalso can be very serious. The most devastating surge in this century was that which struck Bangladeshin November 1970 (Surge No. 49 in Table 2). Human deaths caused directly by the surge wereestimated at 200,000 to 300,000, but there was also enormous economic damage which must have ledto more deaths later. Much of the coastal area of Bangladesh was flooded by sea water, almost alllivestock in the affected area was drowned, and most of the fishing fleet was destroyed (FRANK andHUSSAIN, 1971). Damage due to storm surges in the Bay of Bengal region in the period 1945-75has been estimated at 7000 million U.S. dollars (MURTY, 1984), but this scarcely expresses theimpact of such disasters on developing countries.A number of general reviews and descriptions of individual cyclones and the associated surgeshave been published previously; see, for example, ELIOT (1900), DUNN (1962), RATNAM andNAYAR (1966), and the Bay of Bengal Pilot (ANON, 1966). Notably, FRANK and HUSSAIN(1971) discussed the disastrous effects of the November 1970 storm surge in Bangladesh; COHENand RAGHAVULU (1979) gave a vivid description of the impact of the 1977 Andhra surge; and DASet al. (1978) provided a general review.This paper is intended as an introduction to and a broad review of major aspects of the Bay ofBengal storm surge problem, An account of the factors affecting the generation of storm surges in theBay and their consequences also is presented. During the last few years, efforts have concentrated inthe dynamical approach, in which surges are computed by solving the governing equations todetermine the response of the sea to a model cyclone moving over its surface. Advances made in suchnumerical models are discussed elsewhere (MURTY et al., 1986); the present paper, in fact, representsa condensation of that earlier paper.* Modified from a paper in Progress in Oceanography, 16, 195-233.205

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