Xiaonan Shi

Spatiotemporal variations of suspended sediment transport in the upstream and midstream of the Yarlung Tsangpo River (the upper Brahmaputra), China

The Yarlung Tsangpo River, which flows from west to east across the southern part of the Tibetan Plateau, is the longest river on the plateau and an important center for human habitation in Tibet. Suspended sediment in the river can be used as an important proxy for evaluating regional soil erosion and ecological and environmental conditions. However, sediment transport in the river is rarely reported due to data scarcity. Results from this study based on a daily dataset of 3 years from four main stream gauging stations confirmed the existence of great spatiotemporal variability in suspended sediment transport in the Yarlung Tsangpo River, under interactions of monsoon climate and topographical variability. Temporally, sediment transport or deposition mainly occurred during the summer months from July to September, accounting for 79% to 93% of annual gross sediment load. This coincided with the rainy season from June to August that accounted for 51% to 80% of annual gross precipitation and the flood period from July to September that accounted for approximately 60% of annual gross discharge. The highest specific sediment yield of 177.6 t/km2/yr occurred in the upper midstream with the highest erosion intensity. The lower midstream was dominated by deposition, trapping approximately 40% of total sediment input from its upstream area. Sediment load transported to the midstream terminus was 10.43 Mt/yr with a basin average specific sediment yield of 54 t/km2/yr. Comparison with other plateau-originated rivers like the upper Yellow River, the upper Yangtze River, the upper Indus River, and the Mekong River indicated that sediment contribution from the studied area was very low. The results provided fundamental information for future studies on soil and water conservation and for the river basin management. Copyright

Simulating Bromide Transport from Soil to Overland Flow: Application and Evaluation of Interfacial Diffusion-Controlled Model

The interfacial diffusion-controlled models of chemical transport across the interface of the soil surface and overland flow are physically based and can be easily expanded to include other functional modules to predict chemical loads from soil to overland flow. The efficiency of the model predictions and the veracity of the parameters are critical for accurate estimation of the chemical loads. In this study, the interfacial diffusion-controlled model was employed to simulate the transport process of a dissolved chemical (bromide, Br-) from saturated soil to overland flow. The model parameters were optimized by fitting the analytical solution of the model with experimental data. Comparison between model simulations and experimental observations showed that the model is efficient for predicting (Br-) transport in the soil and overland system. It predicted runoff-concentration data very well and predicted the short-term change in the upper soil profile better than the long-term change in the lower profile. When the mass transfer coefficient estimated by the existing equation was applied in the model, the model underestimated the chemical loads in overland flow by a relative error of 21.5% in this study, which was attributed to the neglect of rainfall impact on the solute transfer from the soil surface to overland flow. DOI: 10.1061/(ASCE)HE.1943-5584.0000495