Environmental change in a mega-delta: Dynamics of salt intrusion in the Vietnamese Mekong Delta

Abstract

Natural resources of the transboundary Mekong River are existential to the livelihood of tens of millions of people. Numerous mainstream and tributary impoundments, overexploitation of groundwater resources as well as excessive sand mining are emblematic of rapid economic development in the region. These significantly strain the riverine resources, and reflect in hydrological regime shift, biodiversity decline and sediment starvation. The Mekong Delta, indispensable to Vietnam’s food and economic security, is impacted by both climatic and anthropogenic drivers of change, within and beyond the delta. Global sea level rise, river discharge anomalies, land subsidence, riverbed/bank and coastal erosion and saline water intrusion are among the most pressing challenges. Among them, increased saline water intrusion, not only has cost the delta millions of dollars yearly in freshwater shortage and crop loss, but is also identified as the key to its strategic land use planning. The present research aims to demonstrate the combined and isolated effects of climatic and anthropogenic drivers of change on past, present, and future dynamics of salt intrusion in the world’s 3rd largest delta. To fill the knowledge gaps, we addressed five topics in this research: 1) we developed a 1D-2D numerical model of the delta to study flow division and barotropic tidal dynamics within the multi-channel estuarine system; 2) we studied the historical trends of tides and salinity in the delta; 3) we developed the first 3D numerical model of the entire Mekong Delta and identified the physical processes leading to increased salinity in detail; 4) we used the 3D model to project saline water intrusion over the next three decades for the delta; 5) we expanded on policy implications of the main findings for the delta and the basin, applicable to similar systems worldwide.