Future sediment dynamics in the Mekong Delta floodplains: Impacts of hydropower development, climate change and sea level rise

• Estimation of future sediment dynamic in the floodplains of the Mekong Delta.
• Plausible ranges of impacts are determined for the delta boundaries.
• Hydropower dams are the dominant impact driver on floodplain sediment dynamics.
• Climate change and sea level rise acts as second-order impact effect.
• The floodplains in the Vietnamese part of the delta respond most sensitive to the expected changes.

The Mekong Delta is under threat due to human activities that are endangering livelihood of millions of people. Hydropower development, climate change and the combined effects of sea level rise and deltaic subsidence are the main drivers impacting future flow regimes and sedimentation patterns in the Mekong Delta. We develop a sensitivity-based approach to assess the response of the floodplain hydrology and sediment dynamics in the delta to these drivers. A quasi-2D hydrodynamic model of suspended sediment dynamics is used to simulate the sediment transport and sediment deposition in the delta, including Tonle Sap Lake, for a baseline (2000–2010) and a future (2050–2060) period. For each driver we derive a plausible range of future states and discretize it into different levels, resulting in 216 combinations. Our results thus cover all plausible future pathways of sediment dynamics in the delta based on current knowledge. Our results indicate that hydropower development dominates the changes in floodplain sediment dynamics of the Mekong Delta, while sea level rise has the smallest effect. The floodplains of the Vietnamese Mekong Delta are much more sensitive to the changes compared to the other subsystems of the delta. The median changes of the three drivers combined indicate that the inundation extent would increase slightly, but the overall floodplain sedimentation would decrease by approximately 40%, and the sediment load to the South China Sea would diminish to half of the current rates. The maximum changes in all drivers would mean a nearly 90% reduction of delta sedimentation and a 95% reduction of the sediment reaching the sea. Our findings provide new and valuable information on the possible future development of floodplain hydraulics and sedimentation in the Mekong Delta and identify the areas that are most vulnerable to these changes.