Integrated inter-basin water transfer (IBWT) modeling for evaluating trade-offs in streamflow and water quality between recipient and donor basins

The Yeongsan (3371.4 km 2 , recipient) and Seomjin (4896.5 km 2 , donor) River basins in South Korea are linked by an inter-basin water transfer (IBWT) system supplying water from the Seomjin to the Yeongsan River basin. An integrated IBWT modeling approach was implemented using the Soil and Water Assessment Tool (SWAT) to evaluate trade-offs in streamflow and water quality between the two basins. The IBWT system was represented by SWAT’s inlet and reservoir operations to simulate transfer processes, and scenarios were designed to represent contrasting conditions. The analysis focused on assessing hydrological and water quality trade-offs under different IBWT scenarios. Increased transfer volumes improved low-flow stability in the Yeongsan River basin, maintaining hydrological stability during dry periods. However, higher transfers also elevated nutrient concentrations (T-N and T-P) and caused localized increases in suspended solids (SS) within urbanized subbasins directly receiving transferred water. When transfer volumes increased, dam release patterns in the Seomjin River basin were altered, reducing downstream flows and leading to higher SS but lower nutrient concentrations, especially during irrigation periods with extended water residence times. Overall, the results reveal that IBWT causes contrasting hydrological and water quality responses between interconnected basins, emphasizing the need for balanced transfer strategies and coordinated management to ensure sustainable inter-basin water resources planning. • Integrated IBWT modeling was implemented using SWAT for the recipient and donor basins. • IBWT trade-offs in streamflow and water quality were evaluated through scenarios. • IBWT scenarios revealed contrasting changes between recipient and donor basins. • Trade-offs emphasize the need for balanced, basin-wide management strategies.