Present to future sediment transport of the Brahmaputra River: reducing uncertainty in predictions and management

Abstract

The Brahmaputra River in South Asia carries one of the world's highest sediment loads, and the sediment transport dynamics strongly affect the region's ecology and agriculture. However, present understanding of sediment conditions and dynamics is hindered by limited access to hydrological and geomorphological data, which impacts predictive models needed in management. We here synthesize reported peer-reviewed data relevant to sediment transport and perform a sensitivity analysis to identify sensitive and uncertain parameters, using the one-dimensional model HEC-RAS, considering both present and future climatic conditions. Results showed that there is considerable uncertainty in openly available estimates (260-720 Mt yr -1 ) of the annual sediment load for the Brahmaputra River at its downstream Bahadurabad gauging station (Bangladesh). This may aggravate scientific impact studies of planned power plant and reservoir construction in the region, as well as more general effects of ongoing land use change and climate change. We found that data scarcity on sediment grain size distribution, water discharge, and Manning's roughness coefficient had the strongest controls on the modelled sediment load. However, despite uncertainty in absolute loads, we showed that predicted relative changes, including a future increase in sediment load by about 40 % at Bahadurabad by 2075-2100, were consistent across multiple model simulations. Nevertheless, for the future scenarios we found that parameter uncertainty almost doubled for water discharge and river geometry, highlighting that improved information on these parameters could greatly advance the abilities to predict and manage current and future sediment dynamics in the Brahmaputra river basin.

Flood Inundation Mapping of the Sparsely Gauged Large-Scale Brahmaputra Basin Using Remote Sensing Products

“…The model was then calibrated by changing Manning's roughness coefficient by comparing the simulated and observed water levels at Bahadurabad. The calibrated Manning's roughness parameter values of the hydraulic model were 0.025 for floodplains and 0.02 for the main channel, which agreed with the values reported in the literature (see, for example, Jung et al [54] and Fisher et al [55]). The hydraulic model was validated with the water level estimated from Jason-2 satellite (see, for example, the Hydroweb portal http://www.theia-land.fr/en).…”

Sedimentation patterns in the Selenga River delta under changing hydroclimatic conditions

“…For instance, impacts of dams can lead to a recession of deltaic wetlands and subsidence of the delta plains (Syvitski et al, ; Yang et al, ). Moreover, climatic changes may influence runoff and erosion in the drainage basin, which in turn affects sediment discharge to the downstream delta (Chalov et al, ; Fischer, Pietroń, Bring, Thorslund, & Jarsjö, ; Leeder, Harris, & Kirkby, ; Törnqvist et al, ). Climate related shifts in the flow regime of rivers (e.g., magnitude of floods) can also influence the supply of sediment and its distribution within deltas (Zhao et al, ; Stern et al, ; Chalov, Thorslund, et al, ).…”

River linking in India: Downstream impacts on water discharge and suspended sediment transport to deltas

“…R 2 values for fitted Q-Q s rating curves range from 0.69-0.95 and are lowest for the Ganga and Brahmaputra Deltas, reflecting current uncertain knowledge of the sediment loads of those rivers as presented in the literature. Darby et al (2015) notes that sediment load estimates for the Ganga range from 390-548 Mt/y, while Fischer et al (2016) finds a suspended load of 260-720 Mt/y. For the Brahmaputra, Darby et al (2015) notes a best estimate of approximately 475-523 Mt/y but acknowledges published values as high as 1100 Mt/y.…”