Cliff Erosion Creates Most Sand on Beaches, Study Says

"I think everybody's accepted the fact that we built too close to the shoreline," Skelly said. "But if it isn't the first row of houses, then it's the next row of houses" that could be affected by erosion, he said. "Somewhere down the line, we're going to have to stop erosion, and it'll be easier to keep building beaches than to allow the land to erode."

Gail Steel, who lives atop a Solana Beach bluff where two seawalls hold back the ocean, said it was easy for environmentalists to say people should give up on the coast.

"If their homes were in jeopardy, I think they would think differently," she said. "I'm all for beaches, believe me -- any one of us who [lives near] the ocean are for beaches. I'm all for having sand and paying whatever it takes to get it here."

In the past, scientists assumed that beaches were largely nourished by sediment-laden rivers dumping into the Pacific. The natural erosion of coastal cliffs was thought to provide only 10% to 15% of the sand, said Scott Ashford, one of the study's authors. Ashford, an associate professor of geotechnical engineering at UC San Diego, and graduate student Adam Young used laser scans to measure erosion from 1998 to 2004 along a 50-mile stretch of coastline between Dana Point and La Jolla.

They concluded that beachfront cliffs provided 68% of the area's beach sand. Rivers and gullies provided 14 and 18%, respectively, they said.

Researchers say that although the study focused on parts of Orange and San Diego counties, the results indicate that coastal experts still don't understand beaches very well and that other bluff areas might deserve a closer look.

"It does suggest that sand held back by coastal armoring is relatively more important than we thought a year ago," said Mark Johnsson, staff geologist for the California Coastal Commission, which must approve requests to build seawalls.

Although the findings don't affect the law that allows oceanfront homeowners the right to protect their property from erosion, Johnsson said, the findings could help change what homeowners might be required to do to be allowed to build seawalls.

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Sands of time

A new report says eroding oceanfront bluffs are a primary source of sand in San Diego County and that protective sea walls prevent erosion that is needed to replenish beaches. Earlier studies said cliff erosion accounted for only 10 to 15% of beach sand.

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Source of sand deposits

Sea cliffs 68%

Gullies 18%

Rivers 14%

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Sandy beaches

San Onofre bluffs produced the most sand in the study area -- 40,500 cubic meters -- from April 1998 to April 2004.

Sand eroded from sea cliffs, annual figures, in cubic meters

Area: Amount

San Onofre: 40,500

Camp Pendleton: 2,900

Carlsbad: 3,200

Leucadia: 4,700

Cardiff: 4,600

Solana Beach: 6,200

Del Mar: 3,700

Torrey Pines: 11,100

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Friend or foe?

Sea walls vary in shape, size and composition -- including rows of telephone poles and stacks of boulder-filled metal cages. Common along the state's coast:

Concrete sea wall: Protects bluff during high tide

Beach: Exposed during low tide

Sources: UC San Diego; California Coastal Commission; Scripps Institution of Oceanography