Riverbank erosion is a major environmental and socio-economic challenge in Bangladesh, particularly along the Jamuna River, which exhibits highly dynamic channel behavior. This study presents a methodology for assessing riverbank erosion using time-series Sentinel-1 Synthetic Aperture Radar (SAR) data. The analysis employs Ground Range Detected (GRD) products with dual-polarization (VV and VH) to extract water-land boundaries and monitor temporal changes. A threshold-based classification approach is applied to derive water masks, followed by bank line extraction and multi-temporal change detection. Results indicate significant lateral channel migration, with erosion predominantly occurring along outer bends and deposition along inner bends. The study demonstrates that SAR data provide reliable, cloud-independent monitoring of river dynamics.