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The Millennium Flood of the Upper Ganga Delta, West Bengal, India: A Remote Sensing Based Study

2022; Springer International Publishing; Linguagem: Inglês

10.1007/978-3-031-04532-5_26

2366-8865

Sayantan Das, Sunando Bandyopadhyay,

Hydrology and Drought Analysis

The Indian part of the Upper Ganga Delta (UGD) is traversed by the Ganga River and its distributary system. As most of these distributaries, in their present condition, are unable to contain the monsoon discharge within their banks, the region is susceptible to frequent flood hazards. The topography of the UGD is mainly characterized by natural levee systems and earthen dykes alongside the rivers. Embankment-induced channel sedimentation, in some parts, has raised the elevation of riverbeds above the surroundings, causing stagnation of floodwater till it percolates down or drains out through the abandoned river courses. The levees often act as barriers and prevent the spilled water from getting back into the main channel. The largest flood in living memory occurred here at the turn of the millennium, in 2000. In September 2000, the remnant of a cyclonic depression triggered heavy downpours in the northwestern part of the UGD and the adjacent Chhotanagpur Plateau. This caused an unprecedented flood that inundated 46% of the UGD region and kept the area waterlogged for more than a month. Breaching the left bank embankment of the Bhagirathi-Hugli River, the floodwater surged southward following non-descript palaeodistributaries like the Gobra Nala and caused significant damages in the districts of Murshidabad and Nadia. Besides this, analysis of elevation models revealed some water movement paths that are undetectable on the ground. Following regional slope, the floodwater then moved across the Jalangi, Mathabhanga-Churni, and Ichhamati river courses to flow southeastward into the North 24 Parganas District, and eventually to Bangladesh. The waters took about a week to cover ~150 km. The pre-, syn-, and post-event satellite images related to the Millennium Flood detected only a few alterations in channel orientations and floodplain morphology. This suggests that the existing channel configuration and floodplain morphology of the UGD are the outcome of slower and lower magnitude fluvial processes. Most inhabitants, residing in the channel bars and near the rivers, have become accustomed to living with the floods during the monsoons. Construction of shelters on the higher areas detachable from the syn-flood images and elevation models can render further protection to these people.