Koeberg NPS, oceanographic engineering services

A range of marine discharge sources and volumes have been modelled for the assessment of the dispersion of cooling water in the near-field, up to 200 m from the outlet, and the far-field, several kilometres from the outlet.

The three-dimensional MIKE by DHI hydrodynamic model was used to model both the near and the far-field dispersion.

The near-field model considered the dispersion due to the local current solved for the transfer of momentum of the outlet flow with the surrounding conditions. The results from the near-field include: steady-state dispersion of the thermal plume and dilutions of conservative tracers at the outlet. Dilutions from the near-field have been used as boundary conditions for the far-field model.

For the far-field model, tidal, wave and wind forcings have been included. The far-field model has been calibrated against historical measurements of ambient water temperature and the extent of the thermal plume.

Results from the near-field solution have indicated that dilutions for some of the discharges are constrained by the geometry of the outlet and result in higher concentration factors than theoretically calculated from the ratio of flow volumes to the total discharge flow.  The concentrations vary for operational conditions based on which of the two main cooling water outlets are in operation.

The Marine Ecology specialist has used the results from both near and far-field in order to determine the specific dilutions of operational discharges and the related impacts around the Koeberg site.