Numerical Modelling of the Suspended Sediment Transport in a Reservoir under the influence of Wind and Temperature

The transport and deposition of suspended sediments in reservoirs not only affect the life span of the storage capacity of these water bodies but also influence the quality of the water upstream of the impoundments. Hence, these processes have been object to a large number of studies, more specifically using numerical simulations. Wind and temperature influence the hydrodynamics of lakes and reservoirs affecting the shape and magnitude of the velocity profiles and also inducing mixing and stratification in the water column. The effect of those two factors on the transport of suspended sediments in reservoirs is here investigated through numerical simulations with the software Delft3D applied to the Passauna Reservoir in Brazil. Furthermore, we tested the sensitivity of the simulations results to two vertical grid systems implemented in Delft3D: Z- and sigma-coordinate systems. The Z-layer system is usually implemented when modelling processes in which vertical exchange is relevant, e.g. thermal stratification. On the other hand, the sigma-layer configuration is the standard selection when modelling suspended sediment transport. The amount of deposited sediments, the deposition pattern and the suspended sediment concentration (SSC) profiles were investigated for the mentioned vertical discretization systems, with the inclusion or not of wind and/or water temperature. We found that the numerical results in terms of transport of suspended sediment are affected by the selection of the vertical coordinate system; furthermore, we show that the inclusion of temperature and wind in the numerical simulations is relevant. This work is a basis for the setup of other models in similar reservoirs, in environments where both fine sediment transport and thermal stratification processes are relevant.