Effects of the Characteristics of Cyclones Hitting Noakhali-Cox's Bazar Coast on Storm-Surges in the Meghna Estuary

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Abstract
Sensitivity study of the storm surges in the worst affected Meghna estuary is vitally needed as it is not done so far. Sensitivity of the surge-peaks in the Meghna estuary is studied by examining the influence of the characteristics of cyclones striking Noakhali-Chittagong-Cox's Bazar coast of Bangladesh. A 1/120° resolution numerical model, whose validity was verified by comparing with the observed data of Bangladesh Department of Hydrography and with those of Surface Water Modelling Centre, is used. The model includes estuarine (and off-shore) islands and bathymetric details of the most-seriously affected northernmost part of the Meghna estuary. Unlike the models which ignore the Meghna estuary, the present model shows that surges in the Meghna estuary do not proportionally increase with the increase in the moving speed of the cyclone and the dynamic effects of barometric forcing in the Meghna estuary can not be represented by linear addition. The surges in the northernmost estuary are strongly influenced by the larger diameter cyclone, but the surges in the southern estuary are not. The cyclone crossing the Noakhali-Chittagong coast is found to produce higher surges than the one crossing Chittagong-Cox's Bazar coast. The inflow angle, which has been ignored in the previous sensitivity studies for the other parts of the Bay of Bengal but which has shown strong variability in the observed winds in the Meghna estuary, is found as a very influential cyclone characteristic. These results also show that the nature of the surges found from the model incorporating the Meghna estuary has a remarkable shallow water sind bathymetric influence and is quite different from those calculated by ignoring the Meghna estuary.

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