Muhammad Nasimul Haque, from the Department of Mathematics of Shahjalal University of Science and Technology, Bangladesh, visited WIT recently to discuss research problems of common interest and during his stay, he gave a lecture on “A Cylindrical Polar Coordinate Storm Surge Model with Radial stretching for the Coast of Bangladesh”.
The Coast of Bangladesh is frequently visited by tropical storms which, along with tidal surges, are the most devastating of all natural calamities befalling the country. The surges take the form of long waves that approach the coast with considerable celerity. Their amplitude increases as they reach the coastal shallow waters. Both tropical storms and associated surges cause tremendous devastation in Bangladesh.
Nasimul’s study is based on developing a cylindrical polar coordinate system for solving vertically integrated shallow water equations to compute tide, surge and their superposition along the coast of Bangladesh. The representation of the curved boundaries of the coast, as well as of the islands, needs special attention when finite differences are used in the solution process. The accuracy of the model depends on a finer mesh near the coast, while this is unnecessary far away from the coast. For the head of the Bay of Bengal, a cylindrical polar coordinate is more suitable as the Bay has approximately a funnel shape. The polar system ensures a finer mesh near the coast and coarser mesh away from it in the tangential direction, but this is not ensured along the radial direction. To obtain a finer mesh near the coast, as well as a coarser mesh far away from it along the radial direction, a transformation of radial coordinates is introduced. This typical grid system is found to be more suitable to represent the head of the Bay of Bengal in a finite difference scheme.
For the purpose of validation of the model, results were obtained at four locations along the coast of Bangladesh for the storms of 1970 and 1981. The computational results were in good agreement with the observations, taking into consideration the uncertainties surrounding the measurements. Water heads were obtained due to tide, surge and tide-surge interaction at Chittagong, Hiron Port and Seadrop for the famous 1970 storm.
The model has shown to be efficient in coupling tide and surge phenomena in the Bay of Bengal. The next step in the research ought to incorporate Oceanographic Meteorological, Meteorological and Geographical data more accurately.
The talk was very well received and gave rise to a lively discussion.
Wessex Institute