n Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese - Modelling of long-term sedimentation at Welbedacht Reservoir, South Africa




This paper describes two-dimensional mathematical modelling of reservoir hydrodynamics and cohesive sediment transport processes, using advection-dispersion theory. Creating such a numerical model involves setting up a suitable curvilinear grid and requires data of the bathymetry, recorded inflows and water levels. It also requires sediment characteristics and transport parameters. These parameters have to be specified by the user based on previous experience and field measurement data.

The Mike21C software from DHI Water and Environment, modified for reservoir sedimentation processes, is used to model the transport of fine cohesive sediment for Welbedacht Reservoir. The reservoir has a relatively narrow basin that constantly experiences extremely large sediment load inputs from the Caledon River. The parameters of flow, sediment characteristics and sediment transport are investigated, calibrated and validated for the Welbedacht Reservoir case study. The calibrated model is then further applied to determine the long-term future equilibrium sedimentation levels as well as future flood levels.


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