River bank erosion risk potential estimation through mechanical and erodibility analysis of soil: A study on left bank of Ganga river near Malda district in West Bengal, India

Abstract

Riverbank erosion is a hazardous and common phenomenon in diara region near Malda district of North
East India during monsoon and post-monsoon periods of every year. One of the signicant causes behind
the erosion is the textural composition and its arrangement along the river bank. The left bank of Ganga
river is texturally very weak along diara region of Malda district. In the present study, the nature of
riverbank soil textural composition has been measured by basis parameters analysis and mechanical
analysis of soil and its erodibility level. Sieve analysis has been done on all collected soil samples and
determines soil basic parameters. The nature of the soil has been derived through the mechanical analysis
of particles after Folk and Worst method. Besides that, the degree of soil erodibility has been analyzed
through the Bouyoucos Erodibility Index and ROM scale after Roslan and Mazidah. The results show that
the erodibility levels become high to the moderate condition along the middle to lower extension of left
bank line and relatively low along with upper extension according to ROM scale. Nature of soil along the
left bank is dominantly sandy which also indicates the vulnerable condition of bank sites. Basic
parameters of soil and its mechanical analysis also reveals that unstable condition exists along with the
whole extension of the riverbank line but instability condition is increasing from upper to lower segment
of bank line. So the risk of riverbank failure can be measured by determining the textural composition of
the soil.