Hybrid Model for Prediction of Initial Dilutions from Outfall Discharges

We present a model for predicting the behavior of a buoyant discharge in a cross-flow. The model is developed through a hybrid of the length-scale and integral approaches. We compare the predictions of the hybrid model with a range of experimental data. In addition we compare the predictions of our model with those from two existing models: the expert system CORMIX1 and the Lagrangian integral model JETLAG. Through these comparisons we are able to show that the hybrid model predicts, with reasonable accuracy, the behavior of effluent discharged at a variety of angles to the ambient current. The hybrid model retains the flexibility of a length-scale model enabling it to be developed more readily to deal with complex flow configurations, such as the staged merging of small groups of discharges. In addition because the model utilizes integral solutions it requires less empirical information to develop than an equivalent length-scale model, which relies solely on dimensional analysis. Through this study we also are able to identify several areas of single-discharge behavior which are not well understood and require further investigation.