Multi-decadal riverbank dynamics along the Sombreiro River in the Niger Delta, southern Nigeria, were quantified using four single-date Landsat images acquired in 1980, 2000, 2010, and 2025, integrated with geographic information system (GIS) analysis and the Digital Shoreline Analysis System (DSAS). The assessment covered the mapped Bukuma–Tombia–Buguma reach, comprising approximately 68.85 km of river channel and 137.70 km of bankline. Historical banklines were delineated from the image-derived land–water boundary and evaluated using the end point rate (EPR), linear regression rate (LRR), weighted linear regression rate (WLR), net shoreline movement (NSM), and shoreline change envelope (SCE). The EPR, LRR, and WLR were treated as rate-of-change statistics, whereas NSM and SCE were treated as displacement statistics. Mean rates of $-$1.63, $-$1.37, and $-$1.48 m yr$^{-1}$ were obtained for the EPR, LRR, and WLR, respectively. The NSM and SCE values originally reported as rates correspond to approximate displacements of $-$63.90 and 76.95 m, respectively, when converted over the 45-year observation interval; however, these values require verification against the original DSAS output. Spatial analysis indicated that 46.98 km (34.0%) of the mapped bankline experienced erosion, 32.45 km (23.6%) experienced accretion, and 58.27 km (42.4%) remained stable. Given the four observations and uneven temporal intervals, the metrics were interpreted as multi-decadal changes and temporal trends rather than continuous annual migration. Potential positional variability associated with acquisition season, river stage, and tidal conditions was considered using a conservative half-pixel screening threshold of approximately 33.5 m. Overall, spatially heterogeneous riverbank behavior was identified, with net retreat exceeding accretion, demonstrating both the utility and limitations of multi-temporal Landsat imagery and DSAS for reconstructing long-term riverbank dynamics in tidally influenced environments.