Water management plans and sea level rise impacts on seawater intrusion in the Red River Delta, Vietnam

Seawater intrusion in coastal areas is now rising as a serious problem for river deltas in the world, especially when high tidal levels occur. Red River Delta plays a paramount role in the economy and society of Vietnam and has already been experiencing the increase in salinity concentrations. The combination of high tidal levels and multi-purposes reservoirs operations in the upstream watershed could exacerbate saltwater intrusion. This research, therefore, analyses the impacts of different water management plans, according to reservoirs operations coupled with sea level rise scenarios, on salinity dynamics in the Red River Delta. Two sea level rise projections referred to RCP4.5 and RCP8.5 emission scenarios have been selected for the simulations of future salinity intrusions in 2050 and 2100. In consideration of the important junction of the 3 main upstream rivers (Lo, Thao and Da River), discharge at Son Tay gauge station is selected as the upstream boundary condition for riverflow. Different discharge scenarios in Son Tay station are, hence, adopted based on statistical analysis of runoff data after the construction of the major reservoirs, started in 1973. Taking into account the 25%, 50%, 75%, 95% exceedance quantiles of the minimum monthly riverflow in Son Tay station combined with 4 downstream sea level rise scenarios, 16 salinity profiles along the Red River Delta reaches were obtained by 1D-hydrodynamic simulations. The results are useful as a guidance to plan multi-purposes reservoirs operations, considering environmental, agricultural, industrial and flood-protection targets.