Analysis of long-term and short-term bankline stability prediction considering seasonal variations: A study in lower Ganga Basin, India

Abstract

River bank instability in the lower Ganga plain has been a major concern since the early 1850s due to its huge catchment flux and transboundary character, especially in the districts of Malda and Murshidabad. This study examines the seasonal dynamics of banklines in the upper and lower Farakka regions. The study assesses seasonal changes in the lower Ganga regions over 68 years (1955–2022) and projects trends for the next 22 years (2022–2044) using a GIS-based Digital Shoreline Analysis System (DSAS) approach. Long-term erosion prevails on the left bank at −19.38 ± 2.83 m yr^-1 (LRR method), with 38.61 % of transects showing a significant (p < 0.05) erosional rate, covering 58.85 % of total erosional transects. The right bank experiences accretion at a rate of 6.82 ± 2.83 m yr^-1, with 27.66 % of transects showing a significant erosional rate, covering 46.10 % of total erosional transects. Short-term fluctuations show erosion-accretion values surpassing the 50 % threshold, highlighting dominant erosion in 1975–1980 and 1985–2015. The non-cyclic erosion-accretion nature unveils erosional processes in 1975–2000 and 2010–2015 and accretional processes in 2000–2010 and 2015–2021 on the right bank during the monsoon season. The dynamics of the projected bank lines exhibit an accretional tendency over the right bank and an erosional trend over the left. Moreover, a strong correlation between the actual and expected bank lines is shown by the $R^2$ value surpassing 0.95 for all seasons on both the left and right banks. The erosional trends are evident in Chachunda at a rate of −152.45 ± 198.92 m yr^-1, while Loharpur and Shikdarpur exhibit erosional rates of −237.88 ± 211.30 m yr^-1 and −243.59 ± 207.91 m yr^-1, respectively, in the lower Farakka. The seasonal long-term and short-term analyses are influenced by various forcing mechanisms like high sediment flux, enormous discharge, and drastic anthropogenic intervention that drives changing foci of erosion and accretion.