The Influence of Avulsion Process on Morphology and Bank Erosion in the Brahmani River, Odisha, India

Floods and cyclones affect the Brahmani River's morpho dynamics. The major flood of 2011 significantly changed the river channel's dynamics. The river exhibits significant spatial and temporal scale variations. Multiple breaching of embankments at different periods makes it more prone to avulsion. The Brahmani River's channel dynamics and avulsion process have been less studied at the spatial and temporal scales. Landsat data (2000-2019) were used to determine temporal changes in the last two decades. The river is divided into ten river classes, and 87 reaches based on their geomorphological characteristics. Planform, slope forming, erosion, accretion and stability parameters are studied to understand the avulsion process. The channel and bar area variability is higher in the middle and lower reaches of the river. Anomalous values of the slope-forming parameters increase the probability of the avulsion process. The erosion, accretion, and stability process determine the impact of the river on bank erosion. All these parameters are integrated into a fuzzy Analytical Hierarchy Process (AHP) to determine the zone of avulsion. The zones of avulsion are validated with rainfall (Indian Meteorological Department) and river gauge discharge data (Department of Water Resources, Odisha). Soil samples are collected from the critical zones (middle and lower reaches) of the Brahmani River to determine the shear strength properties of the soil samples. The detailed geotechnical investigation of soil samples was performed in the Geotechnical laboratory, IIT Roorkee. The shear strength properties of soil samples are determined under consolidated undrained (CU) conditions and unconsolidated undrained (UU) conditions. The numerical simulation of bank slopes was done using PLAXIS 2D software under different conditions. The results obtained from the numerical simulation determined the potential zones of failure.