UCSD Jacobs School of Engineering
University of California San Diego

Bluff Erosion Source for Beach Sand

Bluff erosion in Solana Beach was significant during the sixyear study period in the areas colored red.

UCSD researchers conducting a laser mapping study of about 50 miles of the Southern California coastline were surprised to find that half the beach sand came from rocks and soil that crumbled and washed down from coastal bluffs. Earlier studies have estimated that only 15 to 20 percent of that beach sand came from such erosion.

In a paper presented Oct. 12 at the annual meeting of the American Shore & Beach Preservation Association, structural engineering graduate student Adam Young reported that during the past six years, coastal bluffs lost roughly 3 inches of ground per year. Young and his faculty advisor Scott Ashford report that the unexpectedly high proportion of bluffderived beach sand should be factored into public-policy discussions about “armoring” sea cliffs to stop such erosion.

“While keeping in mind that six years is a brief snapshot in the life of the California coastline, our results call into question the conventional wisdom that coastal bluffs don't contribute that much sand to the beaches,” notes structural engineering professor Ashford. Historical photographs and studies of colleagues also suggest to the UCSD team that Northern California may be just as dependent on erosion to replenish the supply of beach sand.

Young and Ashford used an imaging tool called LIDAR (light detection and ranging), which scans the bluffs with a beam of laser light in a way similar to that of radar. The time required for the laser light to strike the face of a bluff and reflect back to the instrument is used to create a precise 3-D map of the bluff. Scans from one year to the next reveal the annual rate of lost soil. Young won the 2005 Robert L. Wiegel Coastal Studies Scholarship from the California Shore and Beach Preservation Association and he also received the 2005 Education Award from the American Shore and Beach Preservation Association in recognition of his research.

Related Links
News Release: Coastal Bluffs Provide More Sand To California Beaches Than Previously Believed
Website: National Oceanic and Atmospheric Admin. LIDAR mapping site
Website: California Sea Grant
Website: California's beaches
Website: Scoot Ashford profile
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