Mixing of Tee Diffusers in Shallow Water with Crossflow: A New Look

This paper analyzes the mixing of a tee diffuser discharging in shallow water with currents. Experiments are conducted for tee diffusers with different designs discharging in a crossflow. Measurements of dilution are reported and analyzed along with the results obtained by previous studies to investigate the effects of different outfall and ambient parameters on dilution. The effect of ambient current speed, diffuser length, port spacing, port angle relative to horizontal, ambient depth, nearshore distance, and effluent buoyancy on dilution is examined. Previous investigations have shown markedly different effects of ambient current on the dilution of tee diffuser, characterized by the ratio of ambient momentum to discharge momentum. This apparent confusion is resolved by showing that much of the difference can be attributed to the different range of parameters used in different studies. While most studies have focused on minimum dilution within the plume, dilution measurements at the edge of a regulatory mixing zone are considered in this paper because they are important for satisfying regulatory requirements. Measurements of centerline and flux-averaged dilution at the edge of a mixing zone are reported. Recommendations are made for the design of tee diffusers in shallow receiving waters with crossflow.