Beach Study Hopes to Unlock Mystery of Erosion

By Ryder W. Miller

An erosion study at Ocean Beach is currently underway to better understand sediment transport processes and patterns.

Dr. Patrick Barnard, a research geologist for the United States Geological Survey (USGS), is the principal investigator for the study. The study began in October 2003 and Barnard has been collecting data since April 2004. Supporting agencies include The National Park Service and SF Department of Public Works.

"I chose Ocean Beach based on my knowledge of what was going on there," said Barnard, who lived in San Francisco for a number of years.

Because of his knowledge about the erosion problems at Ocean Beach, Barnard found funding through the USGS to explore the local sediment transport processes. Erosion problems continue to damage the parking lot south of Sloat Boulevard since the El Nino/La Nina weather phenomenon of 1997 and 1998.

"I thought it would be an excellent project to provide some independent research," Barnard said.

He pointed out that it was highly unlikely that concerned parties, like the local Surfrider Foundation, US Army Corp of Engineers and National Park Service, would call for the building of a seawall south of Sloat Boulevard, preferring a soft solution (rebuilding with rocks and sand) instead.  The erosion threatens to undermine the Great Highway at the location.  

"We can give them an indication of which way is the best to go," he said.

Tamara Williams, National Park Service liaison for the Golden Gate National Recreation Area (GGNRA), said, "Anything that helps us better understand the coastal processes and the dynamics that are going on at Ocean Beach really does help us in our management decision."

Williams added, "Certainly one of our goals there is to allow the natural processes to operate. The better we understand those, the better we can work with the challenges associated with them."

Sand elevation patterns at Ocean Beach are seasonal. During the tranquil months (April to December) sand accumulates at Ocean Beach and during the winter sand elevation levels shrink due to ocean waves removing the sediment. Barnard has observed sand elevation changes as large as 5 to 6 feet south of Sloat Boulevard.

Recent innovations in field equipment and techniques, remote sensing and computer modeling make it possible to perform detailed analyses of the changing physical processes at Ocean Beach and at other high-energy coastlines.

Barnard said small academic institutions cannot afford to use the techniques the USGS is using in the study, such as a Kinematic GPS (global positioning system), bathymetric surveys, 3D Beach Mapping, Grain Size Analysis, Real-Time Monitoring and Nearshore Mapping (for roughly 1.2 miles out to sea).  Most of the techniques Barnard is using were developed during the last 10 years.

"Our elevation control is very accurate with GPS," said Barnard, who will evaluate the behavior of sediment on the beach on a monthly basis.

Equipment being used for the study includes a camera atop the Cliff House, a GPS system connected to more than half a dozen space satellites, digital cameras to determine sand grain size, personal water craft and all-terrain vehicles.

Some results thus far include an accurate bathymetric modeling of the nearby ocean bottom. Barnard has been able to clearly delineate sand waves moving up and down Ocean Beach due to the power of the tides. 

Barnard hopes to be able to determine the net direction of tidal currents. Some of the unanswered questions involve quantifying the interaction of tidal currents and wave-driven currents, the development of a sophisticated model for sediment transport and the prediction of beach evolution over time.

"There have been prior limitations," said Barnard, who will need more funding for the study to continue. "It will provide data for our coastal managers."

Meanwhile, collaborative efforts led by the California Resources Agency and the U.S. Army Corp of Engineers are underway to develop a California Coastal Sediment Management Master Plan.

These efforts can also help the City resolve the erosion problems at Ocean Beach.

Concerned parties met at the California State Hiram Johnson Building last May.

"There are lots of questions we don't have answers to," said Lesly Ewing, a California Coastal Commission senior coastal engineer. Ewing said 86 percent of the California coast is presently facing erosion problems.

"Sometimes you need to know why the problem is happening," Ewing said.

Clifton Davenport, the Coastal Sediment Management Workgroup project manager at the California Geological Survey, said the California Coastal Sediment Management Master Plan should be completed by July 2005. Barnard hopes to publish some of the results of his Ocean Beach sediment transport research study by the end of the summer.