Discharge-driven rapid bank-erosion and its impact on sediment budgeting in the lower Gangetic plains

Abstract

Riverbank erosion coupled with recurrent flooding has been a persistent problem in large parts of eastern India. Published data on bank erosion along the Ganges in the state of West Bengal suggests an annual average of 8 km2 land-loss during 1969-1999 that potentially affected the lives of nearly a million people and destroyed various human establishments. In this study, we aim to constrain the annual to decadal-scale changes in the path of the Ganges and its impact on sediment reworking in the floodplain. To achieve this, we analyzed LANDSAT imagery from 1987 to 2019 via ArcGIS and a MATLAB-based toolbox called RivMAP. Over the last three decades, the mean reachaveraged migration rates of the Ganges in Malda district of West Bengal vary from 200-600 m/yr and it suffered a net land-loss of ~140 km2, yielding an average annual loss of 4.5 km2. First order mass estimate suggests ~30 Mt/yr sediment yield from Ganges riverbank in Malda, which is ~10-15% of the total annual sediment load of the Ganges expected in Farakka Barrage. Our analysis showcases positive correlation between riverbank erosion and peak annual discharge and therefore, highlights the role of climate on river migration and bank erosion.