Identification of Hydrodynamic Factors for Large-Scale Estuarine Morphological Changes at the Throat of the Lower Meghna River Estuary in Bangladesh

Hatiya Island is an offshore island of Bangladesh located at the throat of the Lower Meghna River Estuary (LMRE). In the previous five decades, the northern section of Hatiya Island and the southern part of the Noler Char coast (opposite coast of Hatiya Island) have seen 12 km and 8.5 km of coastline erosion, respectively. We studied the cause of the continual erosion at the throat of the estuary and discovered that thalweg migration affects the coastline position. In this study, we developed a two-dimensional hydrodynamic model covering the LMRE to investigate the influence of the Hatiya channel's hydrodynamic features and morphological dynamics. We observed a phase difference and time-velocity asymmetry between flood and ebb currents in and around the Hatiya channel using field and simulation data. We created 2D depth average current speed maps for the dry and wet seasons based on simulation findings. We found very high depth average current speeds of 1.75 and 2.5 m/s at the northern part of Hatiya Island, and 2.5 and 3.25 m/s near the southern section of the Noler Char coast during the dry and wet seasons, respectively. We created 2D residual flow distribution maps for wet and dry seasons. During the wet season, we discovered downward residual flow in the Shahbazpur-Hatiya channel and anti-clockwise residual flow on the eastern coast of Hatiya Island, which continued up to the Camper Khal and met with the Hatiya channel. We also discovered a significant residual anti-clockwise circulation flow in the Camper Khal, a downward residual flow at the Shahbazpur channel-Hatiya channel, and residual flow circulation in both clockwise and anti-clockwise directions in the northern section of Hatiya Island.