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

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 Mm(3), 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.

Automated summary

The Lower Ganga River is prone to siltation due to low slope, sediment-charged rivers, reduction in non-monsoon flows, and the impact of the Farakka barrage. This study used remote sensing data and UAV surveys to analyze channel morphodynamics and sediment volumes. Findings reveal significant siltation in several reaches of the Lower Ganga River over the past few decades.