Exploring the Mechanisms and Vegetative Influence on River Bank Migration in Sinuous Channels

Abstract

The migration of alluvial river banks plays a crucial role in the degradation of fertile agricultural land and the displacement of floodplain communities. This study aims to investigate the mechanisms driving riverbank migration in sinuous channels, as well as the protective role of vegetation along the river banks. To comprehend these mechanisms, we conducted experimental studies at the IIT Guwahati fluvial laboratory and numerical simulations using Flow3D. For assessing the impact of vegetation, field observations and satellite imagery analyses were carried out. In examining vegetation influence, a critical stretch of the Nagavali River near Belmam village was identified. Upstream of the village, the outer river bank, lacking vegetation, migrated 100 meters over 12 years, while the downstream vegetated outer bank experienced negligible migration. A similar analysis was conducted on the Kaw River in different regions, revealing that non-vegetative banks migrated nearly 100% of the entire river width over 22 years. To unravel the mechanism behind bank migration, flume experiments and numerical simulations of sinuous channels were conducted. The findings indicated that at the outer bank, secondary currents dominated, emerging as a significant factor in migration. While the numerical study offered a detailed qualitative understanding of the mechanism, it exhibited an error ranging from 22% to 37% from the inner bank to the outer bank. This study extends its focus to a quantitative exploration of floodplain vegetation's role in riverbank protection and proposes a nature-inspired solution, against riverbank migration.