Numerical Simulation of Tidal Level at Selected Coastal Area of Bangladesh

Abstract

The coastal region of Bangladesh is comprised of morphologically dynamic river network, sandy beaches and estuarine system. The interaction of huge fresh water and sediment load coming from the upstream river system and saline waterfront penetrating inland from the sea are the key factors for a vulnerable coastline. Meghna Estuary is located at the central part of the coastline of Bangladesh. The tidal behaviour, upland discharges and wind fields vary distinctly in the coastal areas of Bangladesh. The tides in the coastal and estuarine areas of Bangladesh are semidiurnal in nature. Determination of tidal level for understanding the hydraulic behaviour of the coastal region is very important and crucial for taking any decision of coastal area development. A two dimensional hydrodynamic Depth Integrated Velocity and Solute Transport (DIVAST) model based on FORTRAN program has been set up for Bay of Bengal for simulation of tidal levels. The bathymetry of the Bay of Bengal has been generated with the numerical model DIVAST based on the data of Meghna Estuary Study (MES) phase I and phase II. The simulated tidal levels of the Bay of Bengal model have been calibrated and verified with the observed tidal levels of tidal gauge stations located at Daulatkhan, Tazumuddin, Hatiya, Sandwip, Feni River, Rangadia and Hiron Point locations. The calibration and verification time periods have been considered for spring tidal conditions at dry season from 12 January 2008 to 14 January 2008 and monsoon season from 31 May 2009 to 02 June 2009 respectively. Time of simulation of the model is set for continuous five tidal cycles of 62 hours duration and a total of 40 points of tidal levels are generated. The DIVAST model simulated mean high spring tidal levels in the verification results have been found 1.73 m MSL at Daulatkhan, 1.93 m MSL at Tazumuddin, 4.6 m MSL at Hatiya, 5 m MSL at Sandwip, 4.1 m MSL at at Feni River, 5.4 m MSL at Rangadia and 2.1 m MSL at Hiron Point. The simulated tidal ranges have been observed as micro-tidal at Daulatkhan, meso-tidal at Tazumuddin and Hiron Point, macro-tidal at Hatiya, Sandwip, Feni River and Rangadia. The simulated tidal levels have also been compared with the simulated tidal levels of two other studies and results have been found in good agreement.