Tide–Surge Interaction in the Meghna Estuary: Most Severe Conditions

Abstract

A numerical model with a (1/120)° resolution is used in studying 1) the effects of tide–surge interaction and 2) the effects of cyclone landfall on the Noakhali–Cox's Bazar coast of Bangladesh (i) on the time deviation of the surge arrival from the landfall time of a cyclone and (ii) on the duration of the maximum surge. The present study found that the tide–surge interaction in the Meghna estuary shows, in general, the progressive wave nature of the local tide. If the peak of the maximum surge coincides with the tidal peak near the landfall, the surge propagates toward the north faster than when the surge peak coincides with the tidal trough. Cyclones that make landfall before the arrival of the tidal peak produce higher but shorter duration surges than those that make landfall after the arrival of the tidal peak. If the landfall time of the cyclone is kept fixed, the surge peaks are found to arrive earlier and to be of shorter duration with (i) an increase in the propagation speed of the cyclone and (ii) a decrease in the radius of the maximum cyclonic wind. For the peak of the maximum surge, it may take about 3–4 h to propagate from the southern estuary to the northernmost estuary. The surge, which propagates northward, reaches the northernmost estuary earlier and becomes longer in duration with smaller angles of crossing of the cyclone with the coastline. A slow moving cyclone with a larger radius of cyclonic wind, making landfall in the northernmost area, with a small angle of crossing relative to the Noakhali–Cox's Bazar coastline, and landfall just before the high tide is found to be the most severe cyclone, capable of producing the highest surges in the vast and shallow estuary.