Estuary Processes and Managment - River Dynamics and Integrated River Management - page 512

the discharge. The momentum and the buoyancy of the discharge modify the ambient flow pattern (mean
and turbulent), and the discharge generates its own mean velocity and turbulence field. Rapid dilution of
the effluent is achieved through jet entrainment, and the interaction of the jet momentum and buoyancy
with the ambient current. The pollutant concentration can be reduced 100 times or more by the time the
mixed effluent rises to the surface; when the ambient water is density-stratified (e.g., in the summer), the
sewage plume may “find its own level of density” and be trapped beneath the surface (Fig. 8.53). The typical
time scale in the near field is on the order of minutes, with length scale on the order of the water depth.
Fig. 8.52 Mixing and transport of submerged effluent discharge
Fig. 8.53 Buoyant jet trapped beneath the surface in stratified fluid