New Tool Lets Us Predict Beach Water Quality

July 5, 2015 — Lots of math and a sunny day at the beach.

Doesn’t sound like a match made in heaven, does it? Well, it is for our science and policy staff, who went public this week with a long-in-the-works project – a new statistical model that lets us predict beach water quality.

We’ve just taken the wraps off our “nowcasting” tool, which will allow visitors to some of Southern California’s most polluted beaches to access real-time beach water-quality data online before they hit – or don’t hit – the water.

We’ve spent the past two years working with researchers at Stanford University, who have developed, refined and validated statistical models that provide beach water-quality information similar to a daily weather forecast.

Working closely with researchers at UCLA and Stanford, Heal the Bay is overseeing a pilot program this summer that predicts good or poor water quality for the day at three beaches that have historically struggled with bacterial pollution: Doheny State Beach in Orange County, Santa Monica Beach at the Santa Monica Pier and Arroyo Burro Beach in Santa Barbara County.

The nowcasts are based on the results of predictive computer models that estimate fecal bacteria levels in the surf zone in real time, based on both water quality data (most recent samples and historic trends) and weather conditions (rain, wind and waves). The new tool is a significant improvement from current monitoring and notification methods, which can take days to complete.

Since Memorial Day, Heal the Bay has been running a multiple linear regression model for each of the three pilot beaches on a daily basis to confirm the accuracy of the predictions. Early results have been very promising, with researchers able to successfully predict three significant bacterial exceedances at Santa Monica Beach 24 hours before authorities posted warnings near the Pier.

Heal the Bay is now working directly with local government agencies to provide them nowcast data by 10 a.m. each day. By comparing these computer results to the state’s bacteria health standards, agencies can post warning notices in the morning if warranted, before most people arrive at the beach.

Swimmers at beaches riddled with bacterial pollution face a much higher risk of contracting illnesses such as stomach flu, ear infections, upper respiratory infections and skin rashes.

Starting today, ocean users can now visit to access the nowcasts at the three beaches. Sites are clearly marked as “good” or “poor,” depending on whether the model predicts bacterial levels will exceed state health standards.

Currently, local health agencies throughout coastal California use laboratory analyses of water samples collected at the beach to determine if it is safe for recreational use. Unfortunately, there is a long delay in this approach. It typically takes 24-48 hours to collect the samples, transport them to the lab and analyze the beach water samples. Meanwhile, water quality can change with environmental conditions and swimmers can be put at risk of illness.

In response, researchers have developed the more timely predictive model, which has been used successfully in the Great Lakes region, on the coast of Scotland and at Hong Kong beaches.

If all contiues to go well, we hope to secure future funding to expand the nowcasting model statewide next summer.

The nowcasting tool augments Heal the Bay’s Beach Report Card program, which provides A-to-F water quality grades to more than 400 beaches statewide based on weekly levels of monitored bacterial pollution.

Available online, these weekly grades have become a valuable public health tool for beachgoers all over California. The grading is important because it holds authorities accountable, and has spurred remediation efforts at dozens of chronically polluted beaches.

If you have any questions about the program, please contact Leslie Griffin, our staffer who is overseeing the initiative.