Multi-temporal assessment of river morphological changes using earth observation techniques in Dumuria Upazila of Khulna district, Bangladesh

• Long-term satellite image analysis shows major river network decline in southern Bangladesh. • Small tidal rivers within polders experience the highest morphological degradation. • Hydrological data indicate rising water levels linked to channel aggradation. • Local and morphological observations reinforce satellite-based river degradation patterns. Bangladesh’s deltaic rivers, once lifelines of ecology and livelihoods, have been undergoing rapid degradation over the past few decades due to human interventions and altered hydrological regimes. This study explores the long-term degradation of river systems in Dumuria Upazila, Khulna, over the past four decades, focusing on how structural interventions and land-use change have altered natural fluvial processes. Using multi-temporal satellite imagery, hydrological records, and community perception surveys, the research traces how once active rivers have gradually become narrower, filled with sediment, and disconnected from their natural flow paths. The analysis reveals a drastic reduction in total river length from 492.9 km in 1987 to 203.7 km in 2024, indicating a 59% decline at an average annual loss of 6.14 km (R² = 0.82, p < 0.001). Concurrently, water levels in the Bhadra and Rupsa-Pasur rivers have risen, driven primarily by sedimentation-induced aggradation rather than increased discharge. Community surveys indicated that unplanned polder construction (51.5%) and excessive sedimentation (31.1%) were perceived as the major drivers of degradation. Together, the results show that unplanned polders and infrastructure have increased sediment build-up and hydrological isolation, transforming dynamic tidal rivers into stagnant systems. The study calls for integrated sediment management, adaptive polder redesign, and tidal restoration to maintain both ecological and community resilience in deltaic Bangladesh.