Assessment of Bank Erosion, Accretion and Lateral Migration Using Remote Sensing and GIS: A Study on the Sankosh River of Himalayan Foothills

Channel migration, erosion and accretion are significant geomorphological processes in floodplain regions, impacting both natural and man-made structures. The Sankosh River, a major tributary of the Brahmaputra River, is a good example of a complex and dynamic river system. Erosion and accretion have caused significant problems along the Sankosh River. Local peoples have lost much fertile agricultural land and homesteads in the last few decades, but no related work has been found in this area that highlights this issue addressing erosion and accretion and bankline shifting. The integration of remote sensing and GIS technologies offers a holistic approach to studying river dynamics in this region. Utilizing Landsat TM, ETM+ and OLI satellite data spanning from 1987 to 2021, an investigation was conducted to analyze spatiotemporal variations along the Sankosh River. The modified normalized difference water index, derived from satellite data, is used to assess changes in surface water area. Thirty randomly distributed transects (T1-T30) from three reaches of the Sankosh River served as the basis for the analysis, focusing on river channel morphology, lateral migration, bank erosion and accretion. The findings indicate that from 1987 to 2021, the river eroded approximately 46.50 km2 of land at an annual rate of 1.37 km2/year. In contrast, accretion occurred at a rate of 1.42 km2/year, accumulating a total of 48.27 km2 of land over the same period. The braided nature of the Sankosh River, characterized by a network of numerous branches within its channel, revealed notable shifts in the river's centerline. In reaches A and C, the centerline shifted eastward, while reach B experienced a westward shift during the study period. Let it be known that the research is mainly focused on the assessment of bank erosion, accretion and lateral migration; it surely gives some valuable information to understand the dynamic behavior of the Sankosh River, enabling us to recognize the imperative for sustainable riverbank management strategies. These strategies aim to strike a balance between preserving river ecosystem integrity and addressing community needs and safety concerns.