Estimation and prediction of the oscillation pattern of meandering geometry in a sub-catchment basin of Bhagirathi-Hooghly river, West Bengal, India

Meandering is the winding curve or bends in a river within the floodplain area. Though it is a natural process, it affects the populace by the resultant effect of lateral migration with bank erosion in the floodplain area. The present sub-catchment basin (Nabadwip–Kalyani stretch) of the Bhagirathi-Hooghly river is a vital lifeline of southern West Bengal, which offers adequate water for irrigation, industrialisation, and human habitation. This region is experiencing a favourable geomorphic change through river bank line changing with bank erosion and sinuous meandering. Illegal sand mining and monsoonal flood enhances the meandering process and triggers the reduction of settlement and cropland. The present study elaborates on the migration tendencies and meandering geometry of this zone and tries to predict the future river centerline position in a sinuous course. The study area is divided into 30 cross-sections, which reveals the increasing trend of lateral migration and erosion behaviour towards the eastward section of this region. The spatial and temporal shifting of river centerline and resultant migration observes and predicts through the migration coefficient approach (Hasegawa in Proceedings of the Hokkaido Branch, Japan Society of Civil Engineering, pp 197–202, 1977; Ikeda et al. in J Fluid Mech 112:363–377, 1981. https://doi.org/10.1017/S0022112081000451; Motta et al. in Geomorphology 163–164:10–25, 2012. https://doi.org/10.1016/j.geomorph.2011.06.036) by Arc GIS v 9.3.1. This model indicates the trend of channel width decreasing, with increasing near bank velocity in the crescent of meandering bend in future. The simulated and predicted centerline validates by positive linear relation (R2) and lowest RMSE value in few cross-sectional areas. The oscillation character of meander signifies the amount of discharge in the sub-catchment basin. The unpredictable behaviour of the migration shows a rapid change of meandering geometry through the increasing nature of bank erosion possibilities with peak discharge during monsoon. The study predicts future centerline of the meandering channel and the information on river migration, which will contribute to the plan on bank erosion and denote the vulnerable zonation.