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Understanding sediment dynamics is important for coastal and river erosion mitigation in the Vietnamese Mekong Delta, but this is a difficult work because it is affected by both natural and human factors. The objective of this study is to investigate the accretion and erosion processes in the Bassac and Mekong Rivers from intertidal to fluvial dominated zones by applying MIKE 21. The model was calibrated and validated using in-situ measurements in the 2017 year and the results indicated that the MIKE 21 model is able to simulate reasonably the discharge, water level, and suspended sediment concentration for the study area, with NSE exceeding 0.74 for both calibration and validation periods. Based on the well-calibrated MIKE 21 model, the accreted and eroded river segments in the study area from the river- to tidal-dominated areas were identified. The development of this model is an important step for further applications in understanding impacts of hydrological and sediment alterations from the upstream Vietnamese Mekong Delta on coastal and river morphology in the study area.

River bank processes of erosion and accretion are influenced by both of natural processes and human activities. Therefore, understanding the riverbank processes plays an important role in erosion and accretion mitigations in the Vietnamese Mekong Delta. The objective of this study is to investigate the response of flow and sediment dynamics under impacts of sand mining, river encroachment due to the expansion of fish ponds, and hydrological alteration from the upstream area – a case study in the Mekong River in the Vinh Long province by using MIKE 21 FM model. The calibration and validation results indicated that MIKE 21 FM is one of reliable and reasonable tools for simulating the flow and sediment dynamics in the study area. The responses of flow and sediment dynamics under separate and combined impacts of the illegal sand-mining, river encroachment, and upstream hydrological changes were simulated based on the calibrated model. The results obtained in this study could be useful to propose mitigation measures for riverbank erosion and accretion for management and monitoring