Integrating suspended sediment flux in large alluvial river channels: Application of a synoptic Rouse-based model to the Irrawaddy and Salween rivers

Abstract

A large portion of freshwater and sediment is exported to the ocean by a small number of major rivers. Many of these mega-rivers are subject to substantial anthropogenic pressures, which are having a major impact on water and sediment delivery to deltaic ecosystems. Due to hydrodynamic sorting, sediment grain size and composition varies strongly with depth and across the channel in large rivers, complicating flux quantification. To account for this, we modified a semi-empirical Rouse model, synoptically predicting sediment concentration, grain size distribution, and organic carbon (%OC) composition with depth and across the river channel. Using suspended sediment depth samples and flow velocity data, we applied this model to calculate sediment fluxes of the Irrawaddy and the Salween, the last two free-flowing mega-rivers in Southeast Asia. Deriving sediment-discharge rating curves, we calculated an annual sediment flux of 326^+91-70 Mt/yr for the Irrawaddy and 159 (+78, -51) Mt/yr for the Salween, together exporting 46% as much sediment as the Ganges-Brahmaputra system. The mean flux-weighted sediment exported by the Irrawaddy is significantly coarser (D84 = 193 ± 13 µm) and OC-poorer (0.29 ± 0.08 wt%) compared to the Salween (112 ± 27 µm and 0.59 ± 0.16 wt%, respectively). Both rivers export similar amounts of particulate organic carbon, with a total of 1.9 (+1.4, -0.9) Mt C/yr, 53% as much as the Ganges-Brahmaputra. These results underline the global significance of the Irrawaddy and Salween rivers and warrant continued monitoring of their sediment flux, given the increasing anthropogenic pressures on these river basins.

River Sediment Geochemistry as a Conservative Mixture of Source Regions: Observations and Predictions From the Cairngorms, UK

“…Indeed, some of this variability will contribute to the intrasite variance identified by the ANOVA (Figure 2f). More sophisticated sediment sampling procedures based on hydrodynamics would probably better resolve the larger regional signals from the grainsize induced “noise” (e.g., Baronas et al., 2020; Lupker et al., 2011).…”

Connecting Sediment Retention to Distributary‐Channel Hydrodynamics and Sediment Dynamics in a Tide‐dominated Delta: The Ayeyarwady Delta, Myanmar

“…Despite the similarity in stratification and velocity structure, there was a dramatic seasonal shift in average distributary turbidity. From values at the apex of 0.2–0.4 g/L (Baronas et al., 2020), SSC increased to >1 g/L in the Yangon distributary, remained relatively constant in the Bogale distributary, and decreased slightly in the Pathein distributary (Figure 3). In the Yangon distributary, sediment import was driven by estuarine exchange of turbid water from the northeastern Gulf of Mottoma (Figure 8).…”

“…The current annual discharge at Pyay (Figure 1) is 379 ± 9 × 10 9 m 3 of water and 326 ± 91 Mt of sediment (Baronas et al., 2020). Agricultural irrigation and tributary damming have decreased the total discharge of the river since the first gauging in 1869–1879, when the river discharged 422 ± 41 × 10 9 m 3 of water and 364 ± 60 Mt of sediment (Furuichi et al., 2009; Robinson et al., 2007).…”

“…The Ayeyarwady River (Figure 1) drains through the Central Myanmar Basin, between the Indo‐Burman Range to the west and the Pegu Range to the east. Previous in situ studies have focused on improving estimates of the fluvial and sediment discharge at the inland apex of the Delta (Baronas et al., 2020; Furuichi et al., 2009; Gordon, 1885; Robinson et al., 2007) and on the fate of sediment in the Gulf of Mottoma (Martaban) and adjacent shelf (Kuehl et al., 2019; Liu et al., 2020).…”

Enhancements of Himalayan and Tibetan Erosion and the Produced Organic Carbon Burial in Distal Tropical Marginal Seas During the Quaternary Glacial Periods: An Integration of Sedimentary Records

“…These processes generate the largest sediment discharge to the ocean, ∼25% of the global fluvial sediment flux, through several major river systems, including the Yellow and Yangtze Rivers in the east, the Indus River in the west, and the Ganges, Brahmaputra, Irrawaddy, Salween, and Mekong Rivers in the south (Figure 1; Liu et al., 2020; Milliman & Farnsworth, 2011). Among them, the Irrawaddy and Salween Rivers annually transport 1.9 Mt organic carbon to the sea, suggesting that these rivers may currently be one of the largest riverine sources of organic carbon (Baronas et al., 2020). High sedimentation rates and reduced oxygen exposure of terrigenous matter, as well as a persistent oxygen minimum zone on the continental margins adjacent to these major rivers, sustain the high burial efficiency of terrestrial organic matter both currently (70–85%; Galy et al., 2007) and during the Last Glacial Maximum and late marine isotope stage 6 (Cartapanis et al., 2016; DˊAsaro et al., 2020; Kim et al., 2018).…”