| Among the types of sediment transports in a natural river, behaviors of fine sediments, in particular, the wash load are not so easy to model in numerical simulation. In other words, it is modeled, but it is not easy to verify. Currently the numerical model has treated the wash load as following. It is transported by the flow with transport equation. It generates from river bed as positive source; an erosion term, when river bed degradation (or bank erosion) occurs. It sinks to river bed as negative source; a deposition term, which is relating to the concentration and falling speed. Those erosion and deposition contribute the river bed elevation changes. In order to understand the behavior of fine sediment two kinds of monitoring is conducted in Brahmaputra River. Sentinel-2 NIR band of 842nm wavelength and 10m resolution is implemented to estimate distribution of turbidity in plan-view. Secondly, field observations are carried out with the ADCP and turbidity meter. The mass conservation of sediment in 1-D, as described by the current model, is used to calculate erosion of wash load and suspended sediment. Subsequently, bed load velocity and turbidity measurements are used to discuss the behavior of fine sediment in an area where deposition may be dominated. The results indicate that fine sediment is entrained in the flow due to bank erosion. Deposition of fine sediment is dominated in the region immediately downstream of sandbar where shear stresses are low. The results of the monitoring are well explained by the current model. |
