Quantitative hydro-morphological analysis of the Ganges-Padma River system in Bangladesh

The Ganges-Padma River system, vital for millions of people in Bangladesh and India, is undergoing intricate morphological changes attributed to both anthropogenic and natural influences. The complexity of its evolution and the consequent impacts on riverbank erosion remain unclear, despite its importance for the means of living and sustenance of this region. This study aims to analyze the spatio-temporal planform changes and bank erosion dynamics of the Ganges-Padma reach in Bangladesh and understand the impacts of surficial lithology, river geometry, and hydrology on erosion. GIS-based spatio-temporal planform analysis has been conducted for this study utilizing Landsat satellite images from 1973 to 2020. The planform analysis with surficial lithology reveals a distinct connection between lithology and bank erosion. Riverbanks with non-cohesive materials face more erosion. Additionally, the study suggests the role of high river discharge during extreme flood events in exacerbating bank collapse. Maximum bank erosion was observed during the maximum flood event epochs (1987, 1988, and 1998). It is also found that the Ganges reach is becoming more sinuous with expanding channel width and sandbar area, while the Padma reach is shifting from sinuous to straight to braided over time. Statistical analysis further confirms that erosion is closely linked to river geometry. Increasing sandbar formation (R2=0.48) and river bathymetry (R2=0.50) increase river erosion. These findings provide a quantitative foundation for informed management; for instance, a 1 km2 increase in sandbar area correlates with approximately 134.77 m of channel widening, while the high rate of expansion (92.32 m/y) in the Padma necessitates adaptive infrastructure planning. Understanding these river dynamics and analysis is imperative for the effective management and sustainable development of this expansive river system amidst growing anthropogenic pressures and environmental challenges.