Spatiotemporal assessment of meander geometry and potential cutoff formation in the Gadadhar River of the Himalayan foothills

Abstract

The Gadadhar River is characterized by dynamic processes that shape its channel and behaviour over time. The highly sinuous meandering channel of the Gadadhar River induces geomorphic hazards in both Cooch Behar and Alipurduar districts of West Bengal. The present study assessed changes in channel geometry, including channel width, sinuosity, meander length, radius of curvature and amplitude of meander loops, in the Gadadhar River from 1992 to 2022. For this effective study, Landsat 5 (TM), Landsat 7 (ETM +) and Landsat 8 (OLI) satellite images were used. The results reveal significant spatiotemporal changes in the channel geometry of the Gadadhar River. Over the studied period, the channel width has experienced fluctuations, with Reach A showing a net increase of 23.79 m, Reach B widening by 44.81 m and Reach C experiencing a narrowing of 35.45 m. The meander geometry analysis reveals dynamic shifts in meander amplitude (MA), meander belt width (MBW) and radius of curvature (RC) across key bends such as Karjipara, Santoshpur and Dhadial, with complex trends influenced by neck cut-off formations. The bend tightness index (BTI) fluctuated, with minimum values recorded in 1998 (0.85) and a maximum in 2010 (1.31), indicating variability in the structural integrity of meander bends. Additionally, the channel length exhibited significant variations, with a notable decline of 4.18 km between 2016 and 2022, underscoring the dynamic response of the river. We also observed the formation of meander cut-offs, in which the river carves new channels, creating shortcuts that escape previous meander bends. The research also points out the sites where meander cutoffs have been formed and probable sites where meander cutoffs may occur. Overall, this study provides valuable insights into spatiotemporal changes in channel geometry and meander cutoff formation in the Gadadhar River, which is crucial for effective river management.