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Spatio-Temporal Variability of Channel Planform Dynamics in Response to Spatial Expansion of Brick Kilns: A Case Study of the Downstream Course of Ichamati River, West Bengal, India

2022; Springer Nature; Linguagem: Inglês

10.1007/978-981-16-7373-3_1

2198-3542

Soumen Ghosh, Souvik Biswas,

Flood Risk Assessment and Management

Channel planform reflects the quasi-natural equilibrium in response to energy distribution and carrying capacity of the river. If the river is unable to carry its sediment load, then accretion on the river bed and the formation of several channel bars are inevitable consequences for alluvial rivers. The Ichamati River is a distributary channel of the Mathabhanga River, disconnected from its parent source at Majdia in Nadia district of West Bengal and hardly received any water from the Mathabhanga River except monsoon season. The downstream part of the river is chiefly maintained by groundwater and tidal activity. However, the shortage of water supply from the upstream and unwise downstream human activities has been decreasing the flow velocity and transportation capacity of the river and causing excessive siltation on the river bed. This abundant source of clay-rich fine sediment and perennial source of river water boost the rapid growth of brick kilns along the riverbank over the years. The incursion of sediment-rich tidal water by adjacent brick kilns of the Ichamati River has altered the sediment–water budget of the river. Most of the brick kilns were established within 200 m peripheries of the riverbank violating the guidelines of the Pollution Control Act of 1986 which have directly or indirectly affected different aspects of the channel planform like channel width, depth, meander geometry, cut-off formation process and natural mobility of the river. To study this spatio-temporal planimetric variability of the river, the US Army Toposheet of 1922 and multi-temporal Landsat images of 1976, 1996 and 2016 were used in this study. Besides, the cross-sectional survey of the river was conducted with the help of an echo-sounder and a GPS during 2013–2018. A questionnaire survey was also performed to acquire information regarding the expansion of brick kilns, annual rate of brick production, sediment extraction rate and land-use activities of brick kilns. This study revealed that the natural shifting and meander mobility of the river have been gradually decreasing with the expansion of brick kilns in the last few decades. The channel width was drastically reduced, and the temporal change rate of the channel width was also decreasing due to the control movement of bank lines during 1976–2016. The excessive siltation within the channel causes upliftment of the river bed as measured 9 cm year−1 during 2013–2018. This river is slowly decaying with time and may disappear in future if the proper restoration planning will not implement to revive the river.