River Behavior and Morphological Analysis of a Meandering Channel in the Ganga River System, India

The Rapti River and its tributaries exhibit a predominantly meandering morphology, marked by annual spatial-and-temporal-variations in bend geometry and bankline position. Bankline modifications are most prominent during receding flow-stages due to the accumulation of excess sediment forming point and side bars. A detailed understanding of river behavior both upstream-and-downstream of hydraulic structures is crucial for effective planning, design, and long-term maintenance. This study utilizes remote sensing-and-GIS tools to analyze sediment deposition upstream of barrages and the impact of inefficient energy dissipation from skewed hydraulic jumps downstream. The minimum-sinuosity-index of 1.21 was recorded in reaches exhibiting two-phase underfit morphology, whereas the maximum-value of 2.73 was observed in single-phase reaches with irregular width variation. Prior to the barrage construction, the channel maintained a consistent width of approximately 1000 m both upstream and downstream. Post-construction, the downstream width reduced by nearly 400 m in 1998 and by 800 m in 2006; however, it is projected to return to 1000 m by 2024. From 1975 to 2024, the sinuosity index increased across all morphological types. The lowest average value (1.665) was recorded in partially bank-protected reaches, and the highest (3.139) in reaches with full bank protection. Overall sinuosity increased from 1.64 (pre-embankment) to 1.83 (post-embankment). Bankline migration declined from ~13 m (2006–2008) to ~10 m (2008–2010), stabilized at ~3 m (2010–2016), and reactivated to ~6 m (2018–2024). Sustained riverbank stability necessitates corrective interventions, strategic river training works, and coordinated policy support.