Effects of Density Currents on Sedimentation in Reservoirs

The development of density or turbidity currents causes serious problems for environmental hydraulics in reservoirs. The stream entered to a reservoir can carry sediments, nutrients and chemicals as density or turbidity currents. The fate of sediment and other substances transported by the current depends on the characteristics of the turbidity current itself, i.e. the velocity of fluid, the amount of mixing with reservoir water and the rates of sediment deposition and re-suspension. These are important factors for water quality in reservoirs. A two-dimensional, depth-averaged, finite-volume numerical model is developed to study density currents, driven by non-cohesive sediments. The model has been, then, run with variant input conditions, which could be assessed for their effects on the development of bed and sediment deposits. The amount of sediment deposition and the grain size of deposits have been found to decrease uniformly with their distance from the inlet. The numerical results are compared with some experimental data of turbidity currents and a favorable general agreement is observed.