Assessing the Status of Changing Channel Regimes of Balason and Mahananda River in the Sub-Himalayan West Bengal, India

Abstract

Rapid infrastructural development, triggered by the economic policies implemented in 1991, subsequently modified the river channel planform of the Terai region of northern West Bengal, India, through perceptible channel fragmentation, excessive in-channel sediment mining and rampant landuse alterations of the floodplains. In this context, this study has attempted to assess the impacts of anthropogenic interventions on fluvial regime of the lower reaches of Balason and Mahananda River of the sub-Himalayan region over the last 30 years by adopting a combined methodological framework of remote sensing and field survey. Results showed that initially the naturally vegetated areas had converted into crop land and grass land, tea plantation or bare land, and afterwards, the majority of it had been converted into built-ups. Besides, a noticeable amount of channel narrowing was directly proportionate to unrestricted sediment mining and embanking of the river channels, evidenced between 1987 and 2017. Comparison of measured multi-temporal channel width along with cross-profiles showed remarkable channel narrowing (18.8 m/year) as well as significant bed lowering (3.15 m). Studies reveal that the rivers have started showing signs of losing their existing equilibrium condition and if that happens then that will lead to the sinking of the ground water table, decreasing flood occurrence interval, destabilization of existing infrastructures associated with rivers, and destruction of river ecology. In order to restore the state of socio-hydrological as well as eco-hydrological amenities of these rivers, certain recommendations have also been made towards promoting the wise use of riverine resources by the local communities and policy makers.