ANALYTICAL MODEL OF SALINITY INTRUSION IN THE LOWER MEGHNA ESTUARY, BANGLADESH

摘要

The Lower Meghna River is the main river in the very important area of the Meghna estuary formed by the combined ocean outfall of the Padma-Meghna river system. This coastal region, which is considerably affected by salinity, is extensive and inhabited by a large population. A number of irrigation and drainage projects, for instance the Chandpur irrigation project and the Meghna Dhonagoda project, are located in the vicinity of this river. The salinity levels always exceed an acceptable level for irrigation purpose during dry season. Studies of flow characteristics and salinity intrusion are, therefore, imperative for development of the irrigation systems. The river is substantially influenced by the tides from the Bay of Bengal when interacting with river flows resulted in a complicated pattern which is simplified to its interaction with individual constituents of tides obtained from harmonic analysis. The analytical solution of tide and river flow interaction from Vongvisessomjai and Rojanakamthorn (1989) is applied in this study with the assumption of consistency of cross - sectional area along the river. The obtained results are found to be quite good. Additionally, the analytical solution of salinity intrusion has been described in decomposing the steady state component of salinity from the unsteady component of tidal convection of salinity. Comparison between computed and observed average salinity along the river has been found in good agreement.