Field Experiments Validate New Method for Tracking Beach Pollutants

Scripps Institution of Oceanography / University of California, San Diego

City managers and others must decide the timing and duration of beach closures triggered by contamination events. However, information about the transport and dispersal of pollutants released in the surf zone (the region of breaking waves near the shoreline) is typically lacking. Decisions to close beaches can impact large populations of beachgoers, particularly in popular tourist destinations during peak travel periods.

Researchers at Scripps Institution of Oceanography at UC San Diego have created a model for estimating surf zone waves and currents. The method, based on advances developed through Scripps' Coastal Data Information Program (CDIP: cdip.ucsd.edu), combines predictions of offshore waves
with a model describing how waves break across the surf zone and create currents.

The method was validated recently in Orange County, Calif., during the month-long Huntington Beach Nearshore Experiment 2006, or HB06. Researchers used buoys, moorings, a novel high-tech jet ski, and other instrumentation to study processes involved in the transport and mixing in the surf zone.

"This was the most comprehensive experiment of its kind, and the model passed with flying colors," said Bob Guza, a professor of oceanography at Scripps. "Scripps will be making these kinds of predictions at many coastal locations in Southern California, and this was the first time we were able to confirm the model predictions with results from the field. We plan to extend this valuable information to many other locations and decision makers."

Guza, who led the field experiments with Scripps' Falk Feddersen, will discuss the results of the project at the 2006 American Geophysical Union Fall meeting in San Francisco (Tuesday, Dec. 12, at 9:35 a.m. in Moscone West Room 3009).

In a related presentation, Scripps graduate student David Clark will describe a component of HB06 in which fluorescent dye was used to mimic pollutants mixing in the surf zone (Tuesday, Dec. 12, at 2:10 p.m. in Moscone West Room 3009). The bright pink dye tracer was measured with traditional bottle samples, but also with a custom-built jet ski equipped with GPS technology and water-sampling devices that measured the dye concentration at several locations, including within the surf zone where bottle sampling is very difficult. The jet ski allowed Clark and his colleagues to measure dye concentrations at thousands of locations and to create detailed maps of dye concentration in the study area.

According to Guza, the new data will allow researchers to understand not only where pollutants travel in the surf zone, but how the waves and currents disperse the heaviest concentration.

Another component of HB06 explored concentrations of biological matter. Melissa Omand will discuss the connections between breaking waves and phytoplankton biomass at the shoreline (Tuesday, Dec. 12 at 1:55 p.m. in Moscone West Room 3009).

Seawater samples and hydrographic observations were taken by a small boat, and also with a high-tech jet ski equipped with GPS and instruments to measure chlorophyll concentrations, an indicator of biological abundance. Observations of how phytoplankton and biomass are impacted by waves at the shoreline will aid in understanding complex nearshore ecosystems.

HB06, a project of the Southern California Coastal Ocean Observing System (SCCOOS), was supported by the California Coastal Conservancy, the National Oceanic and Atmospheric Administration, the Office of Naval Research and Sea Grant. For more information about HB06 and SCCOOS see: cdip.ucsd.edu/hb06 and sccoos.org.