A New Chapter in Pollution Studies

As part of an Imperial Beach pollution study, Scripps staff research associate Dennis Darnell tracks pink dye using a GPS-equipped Jet Ski.

Imperial Beach project the latest effort by Scripps coastal scientists to understand dynamics of shoreline water flow

As the summer of 2009 wound down in its final days and flocks of homeward-bound tourists abandoned the coast, a team of researchers at Scripps Institution of Oceanography at UC San Diego was just getting warmed up at the beach.

From Sept. 8 through Oct. 31, Scripps researchers conducted the Imperial Beach Pollutant Transport and Dilution Experiment, or "IB09," the latest in a series of broad beach studies led by Scripps coastal scientists.

As with recent experiments in Huntington Beach in 2006 (HB06), La Jolla/Torrey Pines in 2003 (Nearshore Canyon Experiment, or NCEX), and off Scripps Pier last year, the scientists hope that IB09 will further their understanding of the complex processes, including the strong turbulent motions that mix water along the shore, in order to develop tools to aid beach managers in California.

"In the long run, and it might take a decade or more for the kind of fundamental work we’re doing to actually be incorporated into beach closure models, what this work will do is help us better understand where the pollution goes, how it dilutes, and, ultimately, that could be used by beach managers," said Scripps Professor Bob Guza, one of the lead scientists in the study.

During IB09, a team of 20 scientists, technicians, and engineers undertook a series of experiments designed to examine pollution flow. Imperial Beach in southwest San Diego County was selected as an ideal location for the $1.5 million project not only due to its long, straight shoreline and proximity to outflow from the nearby Tijuana River, but because the city’s officials and area lifeguards were enthusiastic participants in IB09′s operation and success.

During 10 days of the project, the researchers released bright pink dye into the water to mimic how pollution moves and mixes in the surf zone and followed the flow using GPS-equipped Jet Skis.

They also employed drifters, arm-length-sized instruments with antennas that flow through the surf zone to further depict coastal currents. Additionally, an array of instrument frames positioned in the surf zone as well as biological sampling were used to help provide data for a better understanding of the roles played by bacteria and phytoplankton communities in the nearshore waters.

Guza, Scripps principal investigator Falk Feddersen, and colleagues hope to analyze the data and have it ready to disseminate to the broader science community at the February 2010 Ocean Sciences meeting in Portland, Ore. Feddersen praised the 20 hard-working members of the research team for realizing the successes of the IB09 experiments and laying the groundwork for the next chapters of coastal research.

"We’re trying to understand not one particular beach but the overall mechanics, how the process works, so the knowledge we gain can be applied to many beaches down the road," said Guza.

The IB09 project was funded by the National Science Foundation, the Office of Naval Research, California Sea Grant, and the California Department of Boating and Waterways.

—Mario C. Aguilera

November/December 2009