Riverbank Erosion and Settlement Vulnerability Along the Brahmaputra Floodplain: A Geomorphological Perspective

The Brahmaputra River system, one of the most morphodynamically active braided river systems in the world, exerts severe erosional pressure on its floodplain settlements through continuous lateral channel migration, bank undercutting, and episodic avulsion events. This study examines the geomorphological drivers of riverbank erosion along a 180-km stretch of the Brahmaputra floodplain in Assam, India, integrating multi-temporal satellite imagery (Landsat 7 ETM+, Landsat 8 OLI, Sentinel-2A) from 1990 to 2024, Digital Elevation Model (DEM) analysis from SRTM and ALOS-PALSAR, and field survey data from 24 representative erosion-prone villages. Results indicate a net land loss of approximately 2,830 km² in the study reach over the 34-year period, with an average annual erosion rate of 83 km² yr⁻¹. Settlement vulnerability indices computed for 148 riverside villages demonstrate a strong spatial correlation with geomorphic units, particularly with active point bars, mid-channel chars (sandbars), and inner bend deposits. Peak monsoon discharge amplification—aggravated by upstream Himalayan glacier melt—emerged as the dominant proximate driver, while reduced bedload supply from dam impoundment in the upper catchment acts as a secondary geomorphological stressor. The study proposes a spatially explicit Geomorphic Vulnerability Index (GVI) to prioritize erosion-risk settlements for adaptive planning, offering practical implications for disaster risk reduction frameworks in comparable braided river corridors of South and Southeast Asia.