Located in the central part of the coastal region of Bangladesh, the Meghna estuary is that body of water through most of the combined flow of the GBM system is discharged into the Bay of Bengal. A complicated interplay between the forces of the river, tide and the waves creates a complex pattern of sediment displacement in the estuary, which causes morphological changes starting from a time frame of just a few hours to years or even to decades. The Bhola, the largest of the islands of Bangladesh, is located in the western part of the estuary and is subjected to numerous problems to which the estuary is also subjected. Among them, bankline shifting is the major issue which has been relevant for quite some time.
Numerical modelling in combination with satellite images can prove to be a strong foundation for exploring the bankline shifting trend as well as the hydro-morphological analysis of rivers and estuaries if the uncertainties are minimised. The objectives of this study were to enhance the knowledge of complex morphological processes and to develop a qualitative relationship between long-term observed and simulated changes around Bhola Island, Bangladesh. Three methods were explored: literature review, planform analysis and numerical modelling.
Six satellite images taken at an interval of about six years and available for the period from 1973 to 2002 were collected from CEGIS and analysed around Bhola Island both with and without the consideration of sedimentary features. The major factors responsible for the morphological changes in the Meghna Estuary were explored using different long-term modelling tools, scale issues and computational methods using the Delft3D-FLOW model. It was found that the uncertainty ranges of the numerically simulated changes are much higher for the model parameters than the effects of upstream water level variations. The large uncertainty ranges could be reduced if more field data were available for calibration and model verification.
This project was executed in cooperation with UNESCO IHE Delft (MSc study). |
