Fluvial morphodynamics and channel-floodplain interactions of the river Ganga

The Ganga River is one of the major rivers in South Asia, sustaining nearly 600 million people and playing key roles in the region’s water supply, agriculture, ecology, and cultural life. Annual floods in the river trigger heavy riverbank erosion, which reshapes floodplains and affects the livelihoods of riparian communities. This calls for intensive geomorphological investigations to support regional sustainability. The study examined the long-term lateral migration of the Ganga River along with meander dynamics and associated riverbank erosion-deposition dynamics in Bihar, India, from 1972 to 2020. The NDWI and MNDWI indices were applied to delineate the river channel skeletons, and the Fluvial Corridor and Channel Migration Toolbox was employed to assess channel migration patterns. Erosion hotspot analysis was employed using the Getis-Ord Gi* statistic, in combination with Moran’s I index. The results reveal significant channel variations, with an average length migration rate of 20.33 m/year and a shape area migration rate of 9.73 km²/year. The total erosion and deposition exhibit a near balance, covering 1,137.46 km² and 1,107.66 km², respectively. Moran’s I index indicates a clustered pattern (I = 0.91) with erosion hotspots and coldspots measuring 7,584.20 km 2 and 5,276.48 km 2 , respectively. The analysis reveals extensive erosion along the left bank, particularly impacting north Bihar. This has significant economic and food security implications for the society. This study thus furnishes evidence of active channel migration and associated erosion-deposition dynamics in the Ganga plains. The study offers critical insights for policymakers to mitigate environmental consequences through specific mitigation strategies.