Downstream of an effluent discharge to a river there may be a region (called the limited use zone) where concentrations for various water quality parameters meet effluent discharge standards but do not meet receiving water quality guidelines. There is interest in maximizing the dilution in the region near the outfall (the near field) so that the extent of the river which exceeds receiving water quality guidelines is minimized. Jet discharges normal to the direction of flow are a simple and effective means to maximize this dilution. In addition to shortening the length of the limited use zone, jet discharges also provide the benefit of a more reliable design for dealing with buoyant or non-buoyant effluents.

The overall objective of this dissertation is to provide a basis for designing effluent diffusers in rivers. The work focusses on turbulent jet discharges in crossflows. Available literature is reviewed to provide a description of the phenomena and a starting point for this work. Laboratory work by others has been examined and utilized where possible. A photographic investigation has been carried out to indicate the location, width and thickness of jet discharges in deep and shallow crossflows. A field study has been carried out to measure the dilution of various jet discharges in a real river. The field work has been augmented by a laboratory investigation which covers a wider range of discharge conditions. Based on this work, relationships have been developed for the dilution of jet discharges in crossflow. The results of the field work have been used to verify the wide applicability of the laboratory work.

In addition to the near field mixing phenomena, mixing in the far field has been investigated. The two dimensional dispersion equations have been examined in a manner which provide a quantification of the extent of the limited use zone for line source outfalls. Finally, a case history is presented as an example of the application of the findings of this work. This application is particularly relevant to Alberta due to the recent construction in this province of four new pulp mills over the past three years.