Mitigating salinity intrusion in the Vietnamese Mekong Delta: a hydrodynamic modelling study of temporary flow regulation scenarios

Abstract The Vietnamese Mekong Delta (VMD), a critical agricultural region, faces escalating threats from annual salinity intrusion (SI), which significantly compromises agricultural productivity, freshwater availability, and ecosystem integrity. Traditional fixed barriers for SI control, while offering protection, often entail high construction costs and considerable eco-environmental and navigational disruptions. This study investigates the efficacy of temporary cross-section narrowing (TCN) as an adaptive strategy to mitigate SI along the Hau River, a major VMD distributary. A Telemac-2D hydrodynamic model was calibrated and validated using observed water level, discharge, and salinity data from 2016 and 2020 under baseline conditions (without TCN). The calibrated model was subsequently employed to assess the impact of six TCN configurations (Scenarios S1-S6) on reducing upstream saltwater migration. Results demonstrate that TCN can substantially reduce SI, evidenced by a downstream shift of the 4.0 g l −1 isohaline by up to 11.5 km from key irrigation intakes. Furthermore, TCN increased freshwater intake durations from 0 to 19 h and lowered maximum salinity concentrations at the Bong Bot irrigation inlet by 20% to 43% compared to the existing cross-section. Notably, Scenario S3 exhibited the strongest reduction in salinity intrusion and extended freshwater access (over 19 h), followed by S4 and S5. Meanwhile, Scenario S2 offered the most balanced outcome with moderate SI reduction and minimal navigational disruption. This research highlights TCN’s potential as a flexible and adaptable intervention for SI management. However, further investigations into dam design optimization, cost-benefit analysis, and detailed eco-environmental and navigational impacts are warranted to fully ascertain its practical applicability.