Channel morphodynamics and sediment budget of the Lower Ganga River using a hydrogeomorphological approach

Abstract

The Ganga River is one of the largest river systems in the world that has built extensive alluvial plains in northern India. The stretch of the Lower Ganga River is vulnerable to siltation because of: (a) the naturally low slope in the alluvial stretch; (b) the confluence of several highly sediment‐charged rivers such as the Ghaghra, Gandak, and Kosi; and (c) the reduction in non‐monsoon flows because of upstream abstractions of both surface and groundwater. Additionally, the Farakka barrage has impacted the morphology of the Ganga River significantly, both upstream and downstream of the barrage. Large‐scale siltation in several reaches has reduced the channel capacity, leading to catastrophic floods in this region even at low discharges. This work has utilized historical remote sensing data and UAV surveys to reconstruct channel morphodynamics and compute sediment volumes accumulated in the channel belt along the Lower Ganga River between Buxar and Farakka. The work was carried out by dividing the total length of the river into four continuous stretches: (a) Buxar–Gandhighat (GW1, 160 km); (b) Gandhighat–Hathidah (GW2, 106 km); (c) Hathidah–Azmabad (GW3, 182 km); and (d) Azmabad–Farakka (GW4, 132 km). We document that major ‘hotspots’ of siltation have developed in several reaches of the Lower Ganga during the last four to five decades. Sediment budgeting using planform maps provides estimates of ‘extractable’ volumes of sediment in GW1, GW2, GW3, and GW4 as 656 ± 48, 706 ± 52, 876 ± 71, and 200 ± 85 Mm3, respectively. These estimates are considerably lower than those computed from the hydrological approach using observed suspended sediment load data, which assumes uniform sedimentation between two stations. Further, our approach provides reach‐scale hotspots of aggradation and estimates of extractable sediment volumes, and this can be very useful for river managers to develop a strategic sediment management plan for the given stretch of the Ganga River.

Hydrological impacts of altered monsoon rain spells in the Indian Ganga basin: a century-long perspective

“…the Himalayan region in the northern IGB and steep plateau regions in the southern IGB (figure 1(a)), can further exaggerate the flash flood hazards due to the shortening of overland flow travel time (Kelsch et al 2001, Rao et al 2014, Mahmood and Ullah 2016, Swarnkar et al 2020. In addition, these flash flood hazards not only affect the runoff generation mechanism but also intensify the soil erosion and sediment transport rates that lead to offsite and onsite sedimentation problems (Narayana and Babu 1983, Wasson 2003, Swarnkar et al 2018, 2021c, Sinha et al 2023. Figures 10(a)-(f) show that R max has increased significantly as compared to V max and D max after 1960 at all three frequencies across the IGB.…”

Lowland rivers: Geomorphology, human impacts, and management

“…In strong contrast to the sediment deprived lower Rio Negro, the lower Ganga within northern India is a large lowland river with enormous suspended sediment loads, with estimates ranging from 524 Mt/yr to 800 Mt/yr (Sinha et al, 2022). In combination with a dynamic monsoonal flood regime this results in very dynamic channel processes, including high rates of lateral migration and avulsion (Khan et al, 2018; Science , 14 May 2021; Sinha et al, 2022). Individual distributaries laterally sweep across the Ganga plain, resulting in some of the highest rates of lateral migration, globally.…”

“…Entire villages can be lost within a seasonal cycle of river channel adjustment ( Science , 14 May 2021). Sinha et al (2022) map channel bars and planform patterns for seven periods between 1965 to 2017 along a ~600 km segment. In the case of lower Ganga, ‘hotspots’ of siltation within side channels and distributaries have reduced channel capacity, resulting in reduced flow conveyance and increased flooding.…”

“…The 10 special issue contributions herein reviewed concern important fundamental and applied topics within lowland river science, specifically highlighting three key themes. These include ‘natural’ river channel dynamics within settings that vary from the standard body of knowledge (Guha et al, 2022; Rogério et al, 2022; Sinha et al, 2022), geomorphic response to channel engineering (Mossa & Chen, 2022; Marteau et al, 2022; Tang et al, 2022; Wu et al, 2022), and flood basin management in response to environmental change (Keim et al, 2022; Phillips, 2022; Valentine et al, 2022). The categories are not mutually exclusive, and most contributions have linkages across multiple themes.…”

Increasing Flood Frequencies Under Warming in the West‐Central Himalayas

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Northern India is home to large river basins, particularly the Ganga and its Himalayan tributaries, transporting a vast amount of water to the Bay of Bengal annually (Sinha & Tandon, 2014). These river basins are also characterized as some of the world's most disastrous flood-prone regions (Sinha et al, 2022;Wasson et al, 2019), producing catastrophic floods annually. Over 18 million people are directly affected by increasing flood frequencies caused by extreme rainfall events each year (Kumar & Mishra, 2020;Rupa & Mujumdar, 2019;Swarnkar et al, 2021).

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