Integral Modelling of Cooling Water Dispersion in Large Reservoirs with a Dynamically Three-way Coupled Modelling System

A dynamic three-way coupling between a hydrodynamic model (Delft3D), a diffuser slot jet model and a dedicated plant model was set up for the operational modelling of dispersion of cooling water effluent from a power plant at Wheeler Reservoir in Alabama, USA. Wheeler Reservoir is a part of the Tennessee River and is a reservoir bounded by the downstream Wheeler Hydropower Dam and the upstream Guntersville Hydropower Dam. The reservoir typically shows low ambient flow (generally < 0.1 m/s) conditions and significant horizontal and vertical ambient temperature gradients. Small changes in environmental characteristics can have a significant effect on the hydrodynamics and plume behaviour. Recirculation at the power plant is largely influenced by wind driven effects and sloshing effects due to the hydropower dam operations. These ambient conditions in combination with the accuracy requirements for the predictions of the thermal effluent dispersion and recirculation potential, made it necessary to use an advanced, coupled modelling system for the outfall. The COSUMO coupling framework facilitated a coupling between the far field model (Delft3D) and the slot jet near field model, by using the Distributed Entrainment Sinks Approach (Choi & Lee, 2007) in an advanced way. By means of very high resolution (both in space and time) temperature and velocity field measurements, the added value of this dynamic, three-way coupling was analysed. This paper presents the increased accuracy obtained with the enhanced modelling system by comparing this method to the field data and to more traditional modelling approaches.