COAST CITIES — Plumes of pink dye can occasionally be spotted in San Diego waters. No, it’s not a spill or an experiment gone horribly wrong.
Rather, it’s how scientists at Scripps Institute of Oceanography recreate how quickly sewage travels along the shore. Since 2004, they’ve periodically launched the non-toxic dye, along with other technology, at locations like south Torrey Pines State Beach and Imperial Beach to better understand water pollution.
Watching the dye shows researchers the direction of the predominant current that’s carrying the imitation pollution source, and how long it takes for the ocean to dilute it.
The catalyst for the research came about after the number of surfers getting sick from the water spiked about a decade ago, according to Falk Feddersen, a Scripps scientist.
“In the early 2000s there were lots of reports of bad water quality in places like Huntington Beach,” Feddersen said. “People were looking for the causes. On top of that, one thing became clear: there wasn’t information about where pollutants travel once they enter the ocean. And there wasn’t anything about how it gets mixed and diluted.”
A decade later, Feddersen noted that researchers have a pretty firm grasp of how the surf, tides and other factors affect where pollutants move when they’re near the shore. But now the focus is on the unknown — how pollutants behave once they make it past breaking waves and go further offshore.
“There are different variables offshore to account for,” Feddersen said. “There’s the wind and internal ocean waves, for example.”
Measuring offshore versus near-shore variables required Scripps to change up its approach.
Scripps uses the dye and floating devices equipped with sensors to simulate sewage that’s closer to the beach. But for offshore monitoring, researchers follow the dye’s path from the bird’s eye view of an airplane. So far, they’ve done aerial mapping in North Carolina and Imperial Beach. And they’ll do more offshore monitoring in the next month or so somewhere in Southern California, Feddersen said.
“This is the first time this kind of data is being collected,” he added.
Armed with both near shore and offshore monitoring data, Scripps eventually wants to improve San Diego’s beach closure system.
Feddersen explained that currently, because of the time needed to analyze water samples, it can take as long as 48 hours to post advisories or close a beach if the water quality is poor.
Instead of the county being reactive, Scripps researchers could use predictive models to gauge which beaches to close and how long they should remain off-limits to swimmers and surfers.
“Let’s say you knew it was going to rain, we could say when the beaches should probably be closed,” said Feddersen, adding that the findings could be posted online for everyone to access.
It’s a step up from the current system, Feddersen said.
“Immediately after it rains there are still surfers in the water and people fishing,” Feddersen said, adding that it’s only “a few days later when it’s less critical” that they close the beach. By then, pollutants might have already left the surf zone.
Not only could sickness be prevented, but there’s an economic benefit, too.
Unnecessary beach closures would be avoided, giving tourists and locals alike more time at the coast.
“The amount of unnecessary beach closure hours would go down, because the real times when it’s important for the beach to be closed would be known,” Feddersen said.
Lifeguards post advisories in the event of sewage spills or after the county notifies them that testing shows bacteria counts were high at certain beaches. And there’s always a general advisory 72 hours following any rain.
Erik Steenblock, stormwater manager for Encinitas, said closures have been rare for Encinitas beaches.
Steenblock said he wasn’t familiar with Scripps’ research, but added that it sounds promising. He’s also encouraged that the county is looking into water-quality tests that take less time to analyze.
Research funds for Scripps Research are provided by the National Science Foundation, California Department of Boating and Waterways, Office of Naval Research and California Sea Grant.
Feddersen said Scripps research is especially relevant for areas with poor water quality like Imperial Beach. After it rains, sewage from the nearby Tijuana River flows into the ocean, causing potential health issues for swimmers and surfers.
“We’ve gained a lot of knowledge, but there’s more to learn,” Feddersen said.
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