Dynamic coupling of near field and far field models for simulating effluent discharges

In many cases, (processed) wastewater or thermal effluents are discharged into the marine environment, rivers or lakes. To accurately determine the dispersion, recirculation and environmental impacts of outfall plumes, it is important to be able to model the different characteristics of the outfall plume in detail - from the near field (metres around the outfall) to the far field (up to kilometres away). The solution for engineering practice is to combine different types of models (near and far field models) that each focus on specific scales, with corresponding optimised resolutions and processes. However, to adequately describe the hydrodynamic processes on these different scales, it is essential to couple these models in a dynamic and comprehensive way. To achieve this, a dynamic coupling between the open-source Delft3D-FLOW far field model and the CORMIX near field expert system is proposed. This coupled modelling system is able to use the computed far field ambient conditions in the near field computations and, conversely, to use the initial near field dilution and mixing behaviour in the far field model. Preliminary results are presented to provide a first indication of the potential of the method for modelling the complete trajectory of effluent outfall plumes, allowing an accurate assessment of the environmental effects and the design of possible mitigating measures.