CA - Which way does beach sand flow? Studies challenge established views on sand migration along San Diego County coast
A renowned oceanographer who has studied the California coast for decades says new research challenges a well-established notion about how sand flows within the surf and long-shore currents that constantly shape the state's beaches.
Studies show sand doesn't always flow south and in some cases is carried north between the coastal communities, said Reinhard Flick, a member of the Scripps Institution of Oceanography's Coastal Processes Group.
"That's a new finding, and it's important," Flick said. "This strongly suggests that little, if any, sand flows south from Oceanside to Carlsbad."
Carlsbad and Oceanside, like many coastal cities, are losing sand at alarming rates.
The accumulating data could change how local officials approach efforts to preserve their eroding coastlines, particularly sand replenishment projects that cost tens of millions of dollars and can be wiped out by the storms of a single El Niño winter.
Past studies by researchers at the University of California, the California Coastal Commission and the U.S. Geological Survey have shown that the dominant ocean currents carry sand from north to south within what's known as the Oceanside littoral cell, a 50-mile length of coast stretching from the Dana Point Harbor to La Jolla. Most replenishment project are designed with that idea in mind.
"The major agent of sediment transport along the coast is longshore drift, which moves the sand southward," states a recent USGS summary of coastal changes. Southern California beaches are relatively steep, which concentrates sediments in a narrow zone that can vary according to the seasons.
Carlsbad and other San Diego County coastal cities passed resolutions last year opposing an Oceanside proposal to build retention devices, such as rock groins, on the grounds that the structures would stop the flow of sand south to their beaches.
Since then, Oceanside has continued to work on sand replenishment and retention plans, while downplaying the possibility of groins. Three consulting teams are competing to win a design contract for the project, called Re:Beach.
Wave-driven sand transport is complex and detailed, Flick said. Shoreline studies have grown more accurate with the development of improved technology such as Lidar, which stands for Light Detection and Ranging, a system that uses laser pulses to measure the movement of beach materials.
