Effects of sea water level rise and low flow on salinity intrusion in Mekong Delta

Salinity intrusion is one of the major problems in the Mekong Delta (MD). It would increase in the future due to sea level rise and upstream flow decline. In this study, hydrodynamic and salinity model was implemented and applied to the main river systems in the MD, Viet Nam. The model forcing functions consist of tidal elevations along the downstream boundaries and freshwater discharges from the upstream boundaries of the Mekong River with topographical in 1998 and 2005. The bottom friction coefficient was adjusted to achieve model calibration and verification while advection-dispersion coefficients were ascertained through comparison of simulated salinity time series with observations. The model simulation results are in qualitative agreement with the available field data. The validated model was then used to investigate the influence of freshwater discharge and sea level rise on salinity intrusion under sea level rise and upstream flow reduction scenarios. The model results reveal that 2.5g/l saline likely shifted 15km from downstream to upstream in main rivers in comparison to serious salinity intrusion time in 1998. Also, saline intrusion area was expanded most of saline intrusion projects in MD. River discharge is one of dominating factors affecting the salinity intrusion in the main river system of the Mekong River into MD. A correlation between the distance of salt intrusion and freshwater discharge has been established, allowing prediction of salt intrusion for different inflow conditions.