Ocean Outfalls. II: Spatial Evolution of Submerged Wastefield

Abstract

Some of the basic features of submerged wastefield formation in stratified currents are reported in this paper. Dilution increased with distance from the diffuser in the initial mixing region until it attained a maximum value, which is the initial dilution, after which it remained constant. By assuming a model of buoyancy‐induced turbulence collapse, expressions for the observed dependency on current speed in the forced entrainment regime of initial dilution, rise height, and mixing region length were obtained. An expression for lateral spreading in parallel currents was derived which was found to be of the same form as for unstratified currents, except that the rate of spreading in stratified currents is much slower. An expression for the rate of spreading in perpendicular currents was derived by applying results from mixed‐region collapse. An applications example shows that the initial mixing region can extend for several hundred meters downstream from the discharge. Because of gravitational spreading, a line diffuser will produce a wastefield width comparable to the diffuser length for most oceanic conditions, suggesting that Y or similarly complex diffuser configurations are not necessary to produce a widely dispersed wastefield.