Impact of human intervention on assessing downstream channel behaviour of Ichamati River on the lower Gangetic Plain of West Bengal, India

Since the period of human civilization, the hydrological and morphological characteristics of most of the rivers have been intensively modified by human interferences. In this context, the Ichamati River is one of the worst affected distributary channels flowing on the lower Gangetic delta of South Bengal. This tidally active river is streaming on the most densely inhabited district (North 24 Parganas) of West Bengal. The river is gradually decaying over time due to direct and indirect human activities on and along the river. Therefore, the prime aim of this research study is to explain the temporal change of the channel behaviour, especially fluvio-morphological characteristics of the river during 1976–2016. The present study also highlights location-specific causal factors liable for the downstream modification of the channel behaviour. In this research study, channel migration, erosion rate, bank vulnerability zone and channel planform pattern have been assessed using Landsat images of 1976, 1996 and 2016 in remote sensing and GIS environment. Besides, an intensive field survey was conducted for cross-sectional survey of the river. Primary data were gathered from brick kilns through a questionnaire survey for the estimation of sediment extraction rate from the river to prepare the sediment-water budget of the river. This study reveals that the morphological characteristics of Ichamati River have been modified at the human–nature interface and continuous siltation causes gradual upliftment of the riverbed. The channel is gradually narrowing and decaying over time. This study is helpful to understand the current status of the river and helps river scientists for its restoration as well as management planning.