Raw sewage flowing into the Pacific Ocean from the Tijuana River and a Mexican water treatment plant has made it unsafe to swim or surf on San Diego beaches countless times.
So scientists have found a way to forecast how clean or dirty that water will be.
The project is called the Pathogen Forecast Model.
“The overall goal of the project can be stated this way: We want to be able to allow families to know whether they can take their kids to the beach on the weekend,” said Falk Feddersen, an oceanographer at the Scripps Institution of Oceanography, at UC San Diego.
Feddersen and his research team have developed a way to forecast the flow of sewage pollution along the coast by using data about winds, tides, waves and currents.
In one experiment they poured some red dye into the ocean to see how it would move north along the coast.
The result of all this, revealed Tuesday, is a website people can use.
It predicts up to five days how the sewage will flow from its source to beaches such as Imperial Beach, the Silver Strand and Coronado Avenida Lunar. Color codes used on the website represent the levels of contamination.
Red indicates coastal water with a high risk of getting sick. Yellow is a medium risk and green is low.
“So let’s click on Silver Strand,” Feddersen said as he demonstrated the use of the forecasting tool. “And this tells you the percentage of the sewage in the water. So you can see it’s in the yellow. It’s in the high yellow range but then it drops down.”
Feddersen said this pathogen forecaster is the first of its kind.
The contaminant in sewage pollution that makes people sick is called norovirus. He said the next phase of their project will get a better handle on this dangerous pathogen.
“It’s been measured in the ocean before, but it’s always been a one-off kind of thing. It’s never been measured in a systematic way. We are now measuring norovirus in a systematic way,” Feddersen said.
But this forecasting tool won’t solve the problem, which continues to be inadequate treatment of sewage from the Tijuana region.
Pollution on the coast of Imperial Beach is such a problem that water monitors for San Diego County have closed the beach, with only intermittent openings, for roughly the past thousand days.
