Assessing half a century of asymmetric geomorphological change in the Sino-Vietnamese International Boundary River: challenges and pathways for sustainable management

International Boundary Rivers (IBRs) are politically sensitive natural resources, with dynamic evolution that can cause water resource conflicts and territorial disputes between nations. However, due to insufficient attention, quantitative analysis of the long-term dynamics of IBRs and their impacts on riparian states remains critically deficient. This study examines the Sino-Vietnamese Beilun River by integrating multi-source remote sensing imagery (1966–2022), river morphology indices, and the Digital Shoreline Analysis System (DSAS) to evaluate its asymmetric geomorphological evolution and associated bilateral impacts. Results reveal that, over the past half-century, the Beilun River has undergone asymmetric geomorphological changes, altering the riparian land of China and Vietnam. The river has generally shown more deposition than erosion (notably in Segment II), with an average annual narrowing rate of approximately 0.56 m. Erosion rates increased initially but slowed after 2000, while deposition consistently declined. These geomorphological changes have resulted in asymmetric impacts on riparian land: China experienced net land loss in Segments I and III (deposition <erosion), although achieving net gains in other segments. In contrast, Vietnam achieved net land gain across several segments, most notably in Segment II (depositionå erosion). Such imbalances pose significant risks and challenges for equitable resource use and sustainable cross-border management. Building on these findings, the study proposes a sustainable management framework tailored for IBRs that addresses dynamic morphological shifts and promotes collaborative governance. This research provides new quantitative evidence on the complex evolution of IBRs, offering practical recommendations for enhancing their stability and fostering cooperative, sustainable management between nations.