Assessment of the Impacts of Sand Mining on Riverbed Morphology and Riverbank Stability in the Hau River Reach between Long Xuyen and Cho Moi Using MIKE 21 and Geo-Slope Models

Abstract

Sand mining in river channels has increasingly altered river morphology and intensified riverbank erosion in many areas of the Mekong Delta. This study applies the two-dimensional hydrodynamic model MIKE 21 to simulate flow dynamics and sediment transport in the Hau River reach between Long Xuyen City and Cho Moi District, An Giang Province, in order to evaluate the impacts of sand mining on riverbed morphology. In addition, the geotechnical model Geo-Slope/W was used to assess riverbank stability under different sand-mining scenarios. Model calibration results show good agreement between simulated and observed data, with a correlation coefficient R²>0.85 for water level and R²≈0.86for suspended sediment concentration (SSC). Simulation results indicate that sand mining may locally lower the riverbed elevation by up to approximately 2.5 m after 270 days of excavation, while the morphological changes are mainly concentrated within the mining area and gradually decrease toward both riverbanks. After the mining activities cease, the riverbed tends to be naturally refilled by sediments transported from upstream sections and adjacent channels. The riverbank stability analysis using the Geo-Slope/W model shows that the minimum safety factor ranges from 1.448 to 1.761, which is higher than the design safety threshold, indicating that the riverbanks remain stable under the considered mining scenarios. The results provide a scientific basis for assessing the impacts of sand mining on river morphology and support sustainable river-sand management in the Mekong Delta.