Marine Wastewater Discharges from Multiport Diffusers. I: Unstratified Stationary Water
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Volume 130, Issue 12
Abstract
Laboratory experiments on the near-field mixing of buoyant plumes discharged from multiport diffusers into unstratified stationary water are reported. Dilution was measured by a newly developed three-dimensional laser-induced fluorescence system and a microconductivity probe. Significant additional mixing (and dilution) occurs beyond the point where the plume impacts the water surface. This mixing ceases when the turbulence generated by the plumes collapses in the surface spreading layer. The port spacing, , was varied through a range encompassing line to point source conditions. In all cases, the concentration distribution in the surface layer eventually becomes laterally uniform. Measurements of the near-field dilution, length, and layer thickness, and semiempirical equations to predict them are presented. The discharge behaves as a line plume when , and as a point plume when . The additional near-field mixing for a point plume is much greater than for a line plume. Basing diffuser design on near-field dilution rather than impact-point dilution allows the use of far fewer ports, or risers, with considerable potential cost savings, particularly for tunneled outfalls.
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Published In
Journal of Hydraulic Engineering
Volume 130 • Issue 12 • December 2004
Pages: 1137 - 1146
Copyright
Copyright © 2004 ASCE.
History
Published online: Nov 15, 2004
Published in print: Dec 2004
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