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Scripps Scientist Explains Pollution Movement Along Our Coastline

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Posted: Friday, April 26, 2019 10:48 am

Sarah Giddings, PhD, of Scripps Institute of Oceanography, spoke to about 40 people at the Tijuana River National Estuarine Research Reserve, Saturday, April 20, as part of the their bi-monthly speaker series.

Giddings presented the results of Cross Surfzone/Inner-shelf Dye Exchange project that was completed in 2015 and first briefed to the community in 2016. This project made news at the time because it created large pink dye plumes, visible from the beach, that were used to help model how pollution moves up and down the coast.

While the Tijuana river gets most of the news as the most significant source of South Bay pollution there are other pollution sources including storm runoff, the South Bay ocean outfall (discharges treated effluent about three miles offshore) and San Antonio de los Buenos (a Mexican sewage treatment plant located a few miles south in a Punta Bandera). Nevertheless, the Tijuana River remains the source of the most concern to Imperial Beach residents whenever there is heavy rain and sewage bypasses the treatment facility.

Pollution from Punto Bandera generally drifts too far offshore by the time it reaches Imperial Beach to cause problems. However sometimes the odor from the Punto Bandera pollution can be noticed in Imperial Beach which can cause some confusion because people assume that it is coming from the Tijuana River even though the Tijuana River is not flowing and the water quality near the beach is safe.

Giddings showed various time-lapse simulations of how the dye flowed from discharge points along coast and explained that waves, wind, tides and the shape of the ocean floor all affect the movement. Waves and swell direction were the biggest factors that determined how the dyed moved.

In addition to tracking how the dye flowing along the coast, scientists investigated to see if the dye got into the air and how far it traveled inland. They determined that dye was transmitted inland thru the air as a result of the interaction between the waves and the air in the surf zone.

Giddings cautioned that the movement of the dye, which is a proxy for the movement of pathogens and contaminants is not necessarily the same. The full health impact is not well studied, and the actual values of the contaminants is not well known. Further research is required. More information is available at

Giddings would like to see the research they have completed lead to better models and methods to predict the flow of pollution after spills so communities can be more proactive.

The speaker series will continue June 15 at 10 a.m. when Bonnie Ludka, PhD, of Scripps Institute of Oceanography, will speak at the Tijuana River National Estuarine Research Reserve on the topic “Why did the Tijuana River Mouth close in 2016?” for more information on the Tijuana Estuary and its speaker series, visit www.trnerr.

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