Improvement of Nearshore Water Clarity Due to Artificial Upwelling at Power Plant Diffusers

by Robert S. Grove, Environmental Affairs Dep, Rosemead, United States,
John B. Palmer, Environmental Affairs Dep, Rosemead, United States,
Choule J. Sonu, Environmental Affairs Dep, Rosemead, United States,

Document Type: Proceeding Paper

Part of: Coastal Zone '93


The cooling water outfall at San Onofre Nuclear Generating Station, California, discharges heated water at an offshore sea-bed through multiport nozzles which are angled seaward. After 15 years (1974 through 1989) of monitoring the impacts of the outfall, the California Coastal Commission attributed this system to creating excessive turbidity near the discharge zone and thereby impacting a nearby kelp bed through diminished sun light reaching the sea floor. Our new analysis, herein reported, shows this conclusion to be less than complete. It found that the light level at the sea-bed around the outfall has actually increased, rather than decreased, by virtue of the upwelling effect generated by the unique discharge mechanism of the diffusers. Offshore transport of the diluted effluent at the surface gave rise to shoreward drift of cool and clear offshore water at sub-surface, enhancing light penetration to the sea floor in a broad shallow-water zone including the outfall and the nearby kelp bed. The Coastal Commission study had focused narrowly on the turbidity-enhancing function of the plume, instead of taking a broad view of the entire nearshore circulation system of which the plume was only a part. The designers of the diffusers, by incorporating energetic initial mixing capacity, plus seaward and upward momentum in the discharge jets, had anticipated the occurrence of an upwelling system in which the cool and more transparent offshore water will arrive underneath the mixed surface layer.

Subject Headings: Hydro power | Power plants | Sea floor | Water pollution | Water discharge | Water quality | Nearshore | Diffusion | California | United States

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