Modelling of insitu channel migration vis-à-vis bank stability of Brahmani River, Odisha

The process of insitu migration of river channels involves the alteration of morphological parameters, which affects river morphodynamics at both temporal and spatial scales. Over the past 2 decades, the Brahmani River has been subjected to five significant flood events and the impact of Cyclone Phailin. In recent years, there have been numerous instances of embankment failure along the Brahmani River, leading to significant loss of life and property. The present study focused on understanding the mechanism of the insitu migration of river channels by analyzing the temporal scale change from 2000 to 2019. The entire course of the Brahmani River, spanning approximately 799 km, was examined using Landsat data and Bhuvan Cartosat DEM. Planform, erosion, accretion, and stability parameters were analyzed using Landsat data, whereas slope-forming parameters were derived using the Cartosat DEM. The factors of stability, erosion, accretion, sinuosity, and channel area exert considerable influence in directing the river toward insitu migration and embankment failure. The insitu migration zone model was derived by integrating planform, slope-forming, erosion, accretion, and stability parameters using the Analytical Hierarchy Process (AHP). The lower reaches of the Insitu migration model map exhibit numerous reported riverbank erosion locations, which are situated in areas of very high to high vulnerability zones. More vulnerable zones were also identified along the entire stretch of the river. Field and geotechnical investigations of vulnerable riverbanks were conducted along critical zones. Slope stability analysis in PLAXIS 2D using finite element modelling of vulnerable slopes was carried out to validate the Insitu migration model. The simulation of highly vulnerable slopes utilized data pertaining to river water levels to evaluate fluctuations that could result in slope failure. The slopes of the riverbanks in areas designated as very high vulnerability zones in the model are susceptible to erosion, as the Factor of Safety is less than 1, leading to slope failure. This research will prove highly beneficial in gaining a comprehensive understanding of the temporal evolution of rivers in relation to areas of Insitu migration, which will facilitate the formulation of effective strategies by governmental and non-governmental agencies for the management of hazard-prone zones and provision of emergency relief in the region.