Rivers play a crucial role in delivering sediment to the oceans, with deltas acting as key zones for sediment deposition that support ecosystems, human populations, agriculture, and industry. The Vietnamese Mekong Delta, one of the world’s most important and densely populated riv
...
Rivers play a crucial role in delivering sediment to the oceans, with deltas acting as key zones for sediment deposition that support ecosystems, human populations, agriculture, and industry. The Vietnamese Mekong Delta, one of the world’s most important and densely populated river deltas, faces increasing stress as human interventions such as dam construction and sand mining disrupt natural sediment supply, intensifying subsidence, sea-level rise, and erosion. These pressures are further amplified by climate change, which contributes to extreme discharge events, saltwater intrusion, and coastal erosion. While considerable research addresses short-term changes, long-term projections remain limited. This study examines how human- and climate-driven factors shape sediment transport and bifurcation behaviour in the Song Hau distributary over 30 years, by evaluating branch flow
partitioning (symmetry) and the system’s ability to remain in equilibrium (stability).
A Delft3D 2D depth-averaged model, simulating both water flow and sediment movement, is used to examine how climatic and human drivers shape sediment transport and bifurcation behaviour in the tidally influenced Song Hau distributary. Scenarios of altered precipitation (AP), sea-level rise (SLR), sand mining (SM), and hydropower-induced discharge flattening (HD) reveal how changes in upstream discharge, downstream water levels, and bed lowering influence the system. The model performs well, with water flow results showing high accuracy (NSE = 0.90–0.94; RMSE = 0.07–0.21 m) and sediment transport reproduced within 10–20% of observed values, indicating good agreement with observed concentrations.
The results show that climate forcing, through altered precipitation and sea-level rise, generally reduces local extremes of sedimentation and erosion, leading to a more uniform distribution of sediment and flow across the bifurcation and faster stabilisation of sediment partitioning. Altered precipitation increases the system’s export capacity, while sea-level rise increases symmetry by reducing the effect of tides on flow partitioning. This helps maintain throughflow, ensuring consistent export of water and sediment to the sea through both branches. In contrast, human interventions such as sand mining and hydropower-induced discharge flattening increase asymmetry between the Dinh An and Tran De branches. Tran De becomes more dominant in exporting water and sediment, while Dinh An is prone to extreme sedimentation near the river mouth, reducing export capacity. Sand mining has nonlinear
effects, with increasing extraction rates indicating a threshold beyond which the system responds differently. Fluctuations in sediment and flow persist over time, preventing the system from reaching an unchanged sediment distribution. Discharge variability, moderated by hydropower dams, plays a key role in maintaining balanced flow and sediment distribution. Overall, climate change tends to stabilise the system, while anthropogenic interventions lead to more unpredictable outcomes, with sediment distribution being more sensitive than water flow.
The impacts of both human and climate drivers extend beyond the study area, influencing sediment export to the ocean. Ecosystems such as mangroves, which are vital for coastal protection, are highly vulnerable to sediment fluctuations. Effective regulation of human activities, including sand mining and discharge management, is crucial to maintain sediment balance and support the resilience of the delta and its ecosystems under increasing environmental pressures.
